Adventure 40 Hull Design


Well, it’s been a long haul, over two years since I first came up with the concept that became, with the help of many of you, the Adventure 40. A strong, fast, and reliable offshore voyaging boat that you will be able to buy, ready to circumnavigate the world, for US$200,000.

And now, at last, thanks to Erik de Jong, we have a preliminary design. I say preliminary because before Erik does the structural engineering, final hydrostatic analysis, and optimization, we are going to share the design with you, our readers, so that the boat can benefit from the same great process of collaborative thought that yielded such a great specification.

Once we have, over this summer, shared first the hull form—in this post—and then the rig and deck and finally the interior arrangement—in two more posts—Erik will return to his computer and complete the design. The final step in the design phase will be a full check over and evaluation by another naval architect, and then construction of the prototype starts.

As you read these design posts, it’s important to keep in mind that, as I explained in this post, the fundamentals of hull design are well understood, so the key to success is not the application of some high tech black art, but rather formulating a clear understanding of what the boat is intended to do, and then keeping a laser-like focus on that as the boat is designed. Erik has succeeded in this admirably.

If you have not read the original hull form specification post, or even if you have but it was some time ago, please read it now so that you are clear on the goals for the design. Please pay particular attention to the sections on why speed and windward ability are so important.

A Sailor’s Sailboat

Back from reading that post? Great, let’s summarize. The Adventure 40 is not a floating condo, she is not the boat with the biggest interior for a given length, she is not a motor-sailor (although she will motor faster and more economically than most motor-sailors of her length), and she is not the boat with every gadget and contraption known to sellers of marine gear.

She is none of those. She is a sailboat that will be a gas to sail for a day or across an ocean. She will be fast, easily driven, sea kindly, and fun to steer. She is a boat for people that love to sail. If that’s not you, that’s fine, but she is not your boat and we are not going to turn her into your boat, so please don’t ask.

Hull Optimization

OK, now we have the goals firmly in view, let’s dig into the design. The first and most important decision a designer makes is deciding what the hull form should be optimized to do. You see, you can only design a boat to be at its very best in a limited set of conditions. For example, if you design a fast planing hull that will excel downwind in big breeze, the boat will do poorly in light winds and when going to windward. And worse still, if you then load such a boat up with cruising gear, you will end up with a dog that won’t even go downwind well because she can no longer plane.

Given that the Adventure 40 is a voyaging cruising boat, Erik optimized her to be most efficient for speeds that are 90-95% of hull speed, or a little over 7 knots.

This is in keeping with our thinking, proven by tens of thousands of miles in our own boats, that it’s not how fast you go that determines the speed of the passages you make, but rather how often you go fast, even when heavily loaded. In other words, successful offshore boats are optimized for high average speeds over a wide range of wind angles and speeds.

There is one other aspect that determines passage times and that is how comfortable the boat is to be aboard when going fast. Many modern racing designs are theoretically faster than the sea-kindly hull that Erik has drawn, but with a cruising crew aboard both boats, the Adventure 40 will arrive first because the crew on the lighter boat will be forced to slow down due to the motion and slamming.

This brings up an important issue: If a boat can only be truly optimized for one set of conditions and we have aimed the Adventure 40 at around 7 knots of speed with the wind forward of the beam, what about running off, the conditions us cruising sailors love?

Well, by slightly sacrificing performance at low speeds in light air, Erik has pulled off the neat trick of producing a hull form that will be great off the wind too.

To explain why this makes sense, let me digress for a moment. A few weeks ago I was talking yacht design with Steve Dashew and he said something that had me scratching my head:

One of your most important design decisions will be what speed the boat will start motoring at.

And, if you think about it, that makes perfect sense because, if you are, like most cruisers, going to start motoring when things get slow, well, you don’t need to worry about hull optimization for speeds under that threshold.

And he went on to point out that even if you are a purist (or short on fuel) the light air efficiency hit you will take in a hull optimized for higher speeds is in the order of 5%. And for a 40′ boat doing three knots over a 24 hour day, that’s just 3.6 miles—hardly significant. But, on the other hand, if you are in the trades reeling off the miles—where we all want to be—optimizing for higher speeds (in comfort) will get you into port at least a day or three earlier on a typical trans-Atlantic.

Not only that, the hull optimized for higher speeds will steer better when the breeze is up, particularly off the wind in big seas, and said hull will be more efficient at cruise speed under power. One small trade off, many benefits.

By the way, if you are wondering why you can’t optimize for all conditions, the reason is that at low speed it’s skin friction that slows a boat down and at higher speeds it is wave resistance, and you can’t draw a hull that minimizes both perfectly, so we went for the lowest wave resistance.

A Hull That Can Heel

If Erik were designing a motor boat, he would be all done after the above. But sailboats have a major complication that motor boats don’t: they heel. So, not only did Erik come up with a hull form that will work well when flat, but also at 5, 10, 15 and 20 degrees of heel.

I won’t burden you with all the technical details, but this boils down to making sure that the Longitudinal Center of Flotation (LCF) and Longitudinal Center of Buoyancy (LCB) don’t move around as the boat heels because if they do, really bad things happen, like poor steering and scary broaches.

Erik will be putting even more work into this area during the final design process using sophisticated hydrostatic analysis software.

And Carry a Load

There is another important attribute that Erik designed into the hull, and that is the ability to carry high loads, relative to her displacement, without significant performance problems, unlike lighter fat-sterned boats that may outperform the Adventure 40 off the wind when lightly loaded, but will become difficult to steer dogs when fully loaded with cruising gear.

The Right Shape at The Ends


Erik has drawn a lean, mean, sailing machine. But also a boat with enough beam and form stability to be comfortable,

All of this results in a boat that is relatively narrow and fine at the ends with the following trade-offs against a wider, blunter boat:


  • Less strain on the boat, the crew and the rig.
  • Requires a smaller, less expensive and more easily handled rig.
  • Higher speeds in more comfort, particularly with the wind forward of the beam.
  • Less slowing down and smaller leeway angles after being hit by a wave while sailing upwind.
  • A drier cockpit.
  • Much less tendency to pound when going up wind.
  • Easy steering at all reasonable angles of heel.
  • No tendency to bury the bow as the boat heels.
  • The same hull volume for a given displacement.


  • A little more water over the bow area of the boat.
  • Less hull volume in the extremities of the vessel. There goes those two aft cabins.
  • Slightly slower speeds when running off in big breeze.



This is where the tradeoffs get hard. There is simply no getting away from one basic fact: the deeper a boat’s draft, the better she sails when the wind goes forward—faster and lower leeway angles. But, on the other hand, every cruiser wants the shallowest draft they can get. After much agonizing Erik and I settled on six feet (1.82 m).

Based on Phyllis’ and my experience over some two decades and conversations with other experienced cruisers, six feet is a sweet spot. Go shallower on a boat this size, say to 5 feet, and the performance hit is huge but the cruising grounds really don’t open up that much. Go deeper, to say 7 feet, and a lot of doors start to close.

And, if you really want to open up shallow water cruising, you need a draft of about 3 feet and the ability to dry out. In other words, you need an Ovni or a Boréal—great boats but with a very different mission than the Adventure 40.

Erik has gone for a modern keel profile, with much of the weight concentrated at the bottom, while still designing a foil that will forgive steering errors without stalling, and that can be joined to the hull with a large enough area to absorb hard groundings without structural damage.

He has kept the lateral area as small as possible, without losing the ability to resist against leeway at the speeds that are expected to be achieved under sail. This also helps reduce wetted surface, which helps in light air and decreases the chances of a knock-down when hit by a wave in severe weather. I know the last is counter intuitive but, believe me, it’s true. AAC engineering correspondent Matt Marsh has a great explanation of why over at his site.


Erik has gone with a partially balanced outboard hung rudder, turning in a slot in the sugar-scoop stern, a decision that yields many advantages, including:

  • No rudder shaft. At one point we had decided on using carbon fibre for the shaft to get rid of the maintenance problems caused by metal rudder shafts in composite blades, but now the need for a shaft has gone away completely, which will save money we can use in other places.
  • Easier to inspect and repair.

Erik has not yet done the engineering on the rudder, but he is looking at “fusing” it so that it will kick up, rather than break, if hit and/or making the blade comparatively easy to replace at sea, using a cassette type head.

The rudder may look small to you, but that is simply because a boat designed to steer easily like the Adventure 40 just does not need the huge rudders required by boats with shapes driven by interior volume rather than sailing ability.

The Numbers

 Metric  Imperial
Displacement (light ship)  8.00 t  17,600.00 lbs
Payload  2.00 t  4,400.00 lbs
WL Length  11.57 m  37.96 ft
Length Hull  12.72 m  41.73 ft
Beam  3.67 m  12.04 ft
Draft  1.82 m  5.97 ft
Immersed depth  0.59 m  1.95 ft
Prismatic coeff. (Cp)  0.54  0.54
Waterpl. area coeff. (Cwp)  0.66  0.66
Length:Beam ratio  3.79  3.79
Beam:Draft ratio  5.15  5.15


As you can see, although we are just about right on our original target displacement, in this current iteration of the design, the hull length has grown to nearly 42 feet. This change, while surprisingly inexpensive, has yielded all kinds of benefits that will become obvious when we go on to look at the rig, deck and interior arrangement.

Please keep in mind that these numbers are preliminary and subject to change, as we explain here.

What All This Buys You

Let’s just daydream for a moment and put all of this in context:

It’s the fall and we are three and a half days out of Newport bound for Bermuda. We left in company with some friends in a light wide boat with a very wide stern. It has been a broad reach most of the way, so our large tooshed friend has actually pulled away from us a bit and is now just visible on the horizon ahead of us.

But now clouds are building and the wind has been veering all day and finally settles into the southeast, blowing 20 knots true, gusting higher, and quickly building a nasty sea, as the low pressure area to our north drags a warm front over us.

Bermuda is now dead to windward and still 100 miles away. We strap the boat down, trim the vane gear, and shelter under the dodger, as Erik’s hull form starts to show that this is exactly the conditions he was thinking about when he drew her.

A few hours after the shift we pass our friends. Their boat is staggering and rounding up in every gust and being stopped dead and knocked off the wind by every wave. They are barely making 2 knots good toward Bermuda as we romp by, pointing high with a velocity made good of better than double that toward the St. Georges Dinghy Club bar.

We chat on the VHF and they tell us that their lightly built boat is flexing badly and so every hatch and port is leaking, turning the interior into a sodden mess. And, to further add to their misery, the erratic behaviour of the boat is making it impossible to use their vane gear or autopilot, so they are hand steering and getting soaked by every wave while doing it.

There is nothing we can do for them and soon their sails disappear in a rain squall behind us.


A little less than a day later, aided by a bit of tactical cunning playing the shifts, we beat through Town Cut just for the fun of it (don’t try this if you don’t have a Bermudian aboard who knows the waters) and tie up to the Bermuda Customs dock, four and a half days out of Newport.

Four days later our friends are towed in looking battered and bedraggled. Apparently, the slamming got so bad that they were forced to heave-to for a day, which let a secondary low that formed on the front catch them with its associated gale force winds. That resulted in two more days heaved-to before the wind finally veered into the NW and let them make Bermuda. At least the wind didn’t die completely, as it often does after frontal passage, because the water that was getting into their boat sloshed out of the shallow bilges and flooded all the electrics, taking out the engine.

Just a day dream? Hang out at the customs dock in Bermuda in the fall and you will see many realities that look just like the experience of our imaginary friends.

Next up, in a few weeks, we will take a look at the deck layout and rig that Erik has designed.


If you have questions suggestions, please leave a comment. Erik is at sea, on his way to Greenland, but I am in communication with him via satellite email, so if your question is beyond my ability to answer, I can pass it on to him, although it may take a day or so to get his answer and post it.

Like what you just read? Get lots more:

Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

186 comments… add one
  • Roger Neiley May 31, 2014, 3:17 pm

    Great post and good to see the Adventure 40 (or 42?) is coming together.

    I would encourage you to take a look at two important hull dimensions at this point – maximum beam and overall hull height. Those are important considerations if/when the boat is shipped by truck, which opens up a larger market for you and broader cruising grounds for owners.

    Bob Perry drew our Saga 43 with a 12′ beam which means it can be trucked without a lead and chase car. This cuts the trucking cost almost in half. And we found that the keel base to hull height was just an inch short of the maximum height to fit under several bridges during the initial shipment from Ontario to California.

    You are 0.04′ from meeting the 12′ beam requirement, so it would be a shame to miss that threshold by so little, and thus limit your selling territory. Along with this, making the hard dodger removable would decrease shipping height substantially. Just an opinion for consideration.

    Roger Neiley
    s/v SoLunaMare
    Saga 43 #27

    • John Jun 1, 2014, 6:40 am

      Hi Roger,

      That’s a very good idea. We will make a note of it.

      By the way, I really like he Saga and it was one of the boats that inspired much of my thinking on the A40.

    • George M Jun 2, 2014, 5:38 am

      I would just like to add that a similar point holds for the EU. Anything under 3.5m can be transported without permits by authorized vehicles with nothing more than a wide load sign on the back. Over that and you need a permit for each country. Escort vehicles are only required once you reach 4m. So to save the hassle of getting permits in the EU you could shave 17cm off the beam, but it probably isn’t worth it seeing as that wil make the boat more tender with only 183cm draft, and the draft is more important in the EU due to the extensive canal network.

      • Hoftman Guzman Jun 2, 2014, 12:26 pm

        This is the kind of feedback that enriches a design discussion! Thank you Roger and George 😀

  • John Armitage May 31, 2014, 3:29 pm

    Very exciting! A lot has happened in just two years — Congratulations.

  • Douglas Pohl May 31, 2014, 3:54 pm

    Wonderful if you are young forever… and not to re-hash your extensive postings of excellent comments but rather to add my 2-cents worth of wisdom after 30 years of professional marine experiences between the Arctic and humid tropical anchorages follows: I recommend a primary diesel motor vessel with draft flexibility from a center-board like design. The metal hull has a full length box keel which will protect the prop and rudder as best can during a soft grounding. The machinery will be closed-looped keel cooled with dry exhaust. The list of must-have items continues but will not bore everyone so will end here. You are spot on so much of the time but the Adventure 40 new building would require modification to fit what experience has taught me to be a better choice for my adventure cruising needs. One boat cannot fit everyone. Smooth seas!

    • John Jun 1, 2014, 6:46 am

      Hi Douglas,

      Sounds like an interesting boat. Although on of the things I would look at, if doing such a project, is one of the new water separator exhausts, instead of dry and keel cooler. We installed one on our boat in the last repower and are very happy with it.

      Anyway, we will be talking about power boats again some time soon, so hope you will contribute then.

  • RDE (Richard Elder) May 31, 2014, 4:40 pm

    Hi John & Eric
    You forgot to mention how many Dark & Stormies you and your crew put down while waiting at the Dingy Club for your friends on the generic Beneteau to make port—– LOL

    Great to see that the A40 has grown in exactly the right places! As I mentioned some time ago, 12′ is the magic number for many aspects of a functional seagoing interior. If you religiously hold the LOA to 40 ft. you either need to compromise the optimal hull form that Eric has drawn or reduce the beam and thus limit your interior design options. It’s surprising what difference 5 or 6″ makes.

    But— a 42 is a lot more expensive to build than a 40— everybody knows that! Not! Its not the extra hull length that costs a lot to build—– its what you put in it! The bill will come when the dockmaster kicks you out of the 40 foot slips and assigns you to a 50. Easy solution— go sailing!

    ps Yanks are about the only subspecies that still use archaic measures like feet. Since the A40 is no longer a 40, perhaps its time to rename it in Metric!

    • John Jun 1, 2014, 6:57 am

      Hi Richard,

      Glad you like the changes. It really is amazing how close the current design is to the boat you originally envisioned.

      Funny about the feet and meters thing. Its amazing how many metric countries still talk about boats in feet. For example, in my experience, many (most?) Norwegians will always revert to feet when talking about boat length. I think I’m right in saying that the same is true in much of Europe, and certainly in the UK and here in Canada. Not sure if we will rebrand to 42. Maybe not, we have a lot in the Adventure 40 brand. Not the first boat that is a bit longer than the name. Any thoughts?

      As to Dark and Stormies. Are you kidding, we Bermudians only feed that stuff to the tourists. That black rum will kill you! Real Bermudians drink Super Chicken, or in my case whisky (it’s only made in one place and that’s Scotland).

      • RDE (Richard Elder) Jun 1, 2014, 9:41 am

        Hi John,
        The rebranding suggestion was meant to be a bit tongue in cheek. On the other hand it is amazing how many uninformed boat show buyers brag about buying the biggest 40 footer on the dock, but wouldn’t consider a 42 because it is “too big to handle.” Or how a manufacturer can convert a 40 foot boat to a 42 by adding a bowsprit or sugar scoop and sell it for $75,000 more—–. Fortunately A-40 buyers are too smart to fall for such ruses!

        • Laurent Jun 1, 2014, 11:04 am

          Looking at the projected hull drawing, it looks like you can get down to 40′ by getting rid of the scoop and cutting the bow tip without much altering of the water-lines, just using an inverted-cone bow with same buoyancy and same water-line excepted in the last foot of boat-length.
          Might make sense for marina fee and/or for marketing purpose about this 40 or 42 feet issue….

          • John Jun 1, 2014, 2:11 pm

            Hi Laurent,

            I hear you, but we don’t want to lose the scoop since its all part of getting an outboard rudder and a vane gear in an elegant way.

            Also, cutting the bow overhang will give us anchor stowage problems and other issues. Wait until you see Erik’s way cool deck layout and all will become clear.

            Bottom line, the whole ethos of the Adventure 40 is putting function first and marketing stuff second. Further, anyone who is not going to buy the boat because it is two feet longer than 40’…well, I don’t think they get it, so there not going to buy the boat anyway.

    • Ian Tyler Jun 3, 2014, 8:17 am

      Europe may be metric but their boat names/models are still imperial – just look at the Bavarias and Beneteaus!

  • pat synge May 31, 2014, 7:52 pm

    This certainly appears like a nicely balanced hull form and should steer easily but, despite what you have written John, I reckon she will still slam quite heavily when being sailed hard to windward in short steep seas.

    • John Jun 1, 2014, 7:17 am

      Hi Pat,

      Not sure why you would say that. I have advantage of being able to look at the lines full screen in 3D and I just can’t see her slamming with the fine bow and the shape of the sections forward.

      You may want to click on the sections drawing (to enlarge) as seen from forward (right half of plan) and let your eye traverse the forward six sections while blanking out the ones further out (aft). This will help visualize how fine and V’ed these sections are. By the way, this one of the areas Erik was able to do really good things with by lengthening the boat (see RDE’s comment).

      Also, the hull is very much based on Erik’s own boat Bagheera which has been tested extensively to windward, including a very stormy east to west northern trans-Atlantic, almost all hard on the wind. In fact, as I understand it, Erik’s Dad slept in he forward cabin for all of that trip, which is a tribute to the boats sea kindliness…and the strength of that man’s stomach!

      Having said that, such things will certainly be looked at carefully in the final design review.

      • pat synge Jun 1, 2014, 7:20 pm

        I agree that the first 6 sections show a fine entry but surely these only represents ~10% of the LOA. By the time you get to section 20 ( ~30% LOA) the bottom of the hull is quite rounded. In steep short seas I still reckon she will slam unless slowed up. I fully appreciate that one cannot achieve the impossible and that there’s no way you are going to consider a deep V and slack bilges. Nor would I.

        As for whisky only being “made in one place and that’s Scotland” I will again offer a contrary opinion. As a Scot I have to draw your attention to Sullivans Cove single cask malt which was named the world’s best single malt whisky at the World Whiskies Award. Tasmanian!

        • John Jun 2, 2014, 5:10 pm

          Hi Pat,

          Yes, any boat of this size will have to slow up once the waves get really big. Even our own boat at nearly three times the size can’t keep going full out once the true wind gets over about 30 knots.

          Having said that (there I go again with that phrase) I still think that the A40 will be better to windward in a the ocean than just about anything out there, and will be able to keep going comfortable up to 25 knots true. Yes, the sections round out as you go aft, but keep in mind that she carries much less beam forward than many boats today, and that’s a lot of why she won’t slam, as well as Ved sections.

          Oh yes, if you want to send me a case of that Tasmanian Whisky, I will be happy to render an opinion. 🙂

  • bruno May 31, 2014, 10:52 pm

    any hull should be nice and attractive at first … this one is ! Congrats

  • pat synge Jun 1, 2014, 12:05 am

    The question of aesthetics has reared its head. Thanks, Bruno!
    Obviously this is completely subjective with beauty being firmly in the eye of the beholder.

    When I designed my boat 30+ years ago with a flush deck (raised topsides) and a sugar scoop stern I heard (usually second hand) many unfavourable comments. Now as I look around it looks quite conventional and almost sleek (in a multi-chine sort of way).

  • Brett Eaglen Jun 1, 2014, 2:07 am

    I know this is early in the discussion but on our 43ft Interlude we had a stern hung rudder in a divided scoop similar to the described. On the trailing edge of the rudder was a trim tab connected to the smallest electronic autopilot. It has done 1 1/12 circumnavigations, even steering when surfing to over 20 knots on one occasion. Great set-up. Cheap, reliable, easily adapted, minimal energy use… it was a modified version described in Gerard Dijkstra’s book on self steering. Enjoying the process.

    • John Jun 2, 2014, 1:25 pm

      Hi Brett,

      I know very little about trim tab steering gears, but it’s certainly a suggestion worth looking at.

      Having said that, I was under the impression that trim tab gears are more fussy and difficult to get to steer right, and therefore a pendulum servo gear might be a better bet because many of the boats buyers will be relative beginners. Any thoughts?

      • Peter Thornton Jun 23, 2014, 7:26 am

        Hi Brett/John and all interested. I think the use of a trim tab is a great suggestion, it’s effective, light, cheap, powerful and well suited for coupling a small tiller pilot directly to. The main reason they are not more common is they really suit transom hung rudders best, and you cant just go out and buy one and bolt it to the back of the boat like a servo pendulum windvane. It really fits with the ethos of the A40 it just needs some thought at the design stage rather than buying a bolt on solution further down the track. It also saves thousands on the price of an autopilot. Tiller steer and auto pilot don’t go together too well unless you can fit a hydraulic ram below decks but the complexity and cost go way up. Tiler steer is great and has a lot to recommend it, likewise with transom hung rudders. one of the major benefits of both is to be able to easily rig a trim tab. it would be a shame to miss this opportunity. Keep up the great work.


        • John Jun 23, 2014, 7:51 am

          Hi Peter,

          That all makes sense, we will keep it in mind.

  • C Dan Jun 1, 2014, 12:46 pm

    LOA is 42, LWL is 38… I see no problem calling this a 40 foot boat 🙂

    • John Jun 1, 2014, 6:53 pm

      Hi C Dan

      Works for me.

  • C. Dan Jun 1, 2014, 5:56 pm

    I am super excited to see the rig and deck layout. The interior will be great, too, I am sure, but interior layouts seem to generate so much controversy that I could also skip the collaborative process there and just trust you guys to do a good job.

    Mostly, though, I think the best design elements will come from the prototyping process, so I am hopeful to see hull #0 in the water in 2015. Maybe that is too optimistic.

  • John Jun 1, 2014, 6:54 pm

    Hi C. Dan,

    I hear you on the interior, but I fear we will have to fight the good fight.

    2015 for the prototype…Erik will probably kill me for this…could happen.

    • Hoftman Guzman Jun 2, 2014, 1:09 pm

      I’ll be there for you, John 😉 LOL

  • Steve Gallion Jun 1, 2014, 11:28 pm

    Looks like a good start, but I would like some more information about the keel to hull joint, and the construction of the keel itself.

    Also, could a copper mesh ground plane be incorporated into the layup below the water line for HF grounding? If possible, NMEA recommends at least 100 sq ft.

    Can’t wait to see more!!!

    • George M Jun 2, 2014, 6:16 am

      Yes, I would also like some info on that. Please do consider flaring the root of the keel and using bronze keel bolts.

      • John Jun 2, 2014, 9:29 am

        Hi George,

        See my comment to Pat and Laurent. I like bronze too, but until Erik does the final engineering and costing, we can’t commit to any construction details. Having said that, although I don’t think it will be required, I would rather put the price up than build a bad boat, and so would Erik.

        Keep in mind that low 10 year (at least) cost of ownership is our overreaching goal.

    • John Jun 2, 2014, 9:33 am

      Hi Steve,

      Good idea on the copper mesh. Having said that, SSB is fast going the way of the buggy whip—I know that will raise howls, but it’s true—and if we are going to hit the price point and build a great boat, we are going to need to stay really focused on what really must be included.

      • Douglas Pohl Jun 2, 2014, 10:54 am

        Everyone should urge SSB manufacturers like Icom et al to add ALE ( to their radios ASAP (even as a $500 option) else realize their SSB-HF business will as you say… go the way of the buggy whip.

        • Douglas Pohl Jun 2, 2014, 11:21 am

          The buggy whip continues to fade faster than you can check on ALE… Google reportedly plans to spend $1B on Internet satellites.

      • Simon Wirth Jun 10, 2014, 11:28 am

        Hei John
        As a radio amateur I have to say that you are right about SSB.
        The only way I see HF as a reall plus is only in morse code. There is nothing like a single carrier if the connection is getting bad.
        I got to know ALE on HF… I, for my part, will gladly take the stright key any time before using ALE. Just my two cents.
        Thanks for the great post, can’t wiat for the rest!

    • Enno Jun 16, 2014, 9:42 am

      I’m with Steve concerning the copper mesh.
      I’m using SSB for email, grib files and fax. Once installed its free. Try that with Iridium and co. This makes it especially attractive for low budget cruisers, which is the target group for the A40.
      A copper mesh would also be an item which is easy to install during build but difficult and less effective to refit.

      • John Jun 17, 2014, 7:18 am

        Hi Enno and Dick,

        It just struck me that the A40 will have an external metal keel, probably lead, which I think will make a pretty good SSB counterpoise without the need to resort to imbedding copper mesh in the laminate, with the attendant chance of manufacturing problems.

        Also, here’s another nice simple alternative.

  • Steve Gallion Jun 2, 2014, 1:19 am

    I’m thinking about renting a booth at Strictly Sail – Pacific next year (on my dime) to promote the Adventure 40 (or 42?). Could you have a promotional packet ready by April 2015?

    If that sort of promotion fits into the business plan, I’d be glad to do it. (If given a green light on this, I could use a few S.F. Bay area volunteers.)

    • John Jun 3, 2014, 8:05 am

      Hi Steve,

      What a wonderful offer, Thank you. Sounds like a great idea.

      As to a promotional package, if you mean glossy brochures and videos etc, I suspect that there will never be any of that. I know that sounds crazy, but if we are going to hit the price point, we need to cut marketing expenses to the bone. Or to put it another way, as a potential A40 buyer, I’m sure you would rather see your money go into a stronger keel to hull joint than a broshure.

      Having said that, we already have, I think, an even better answer to “promotional material” than that traditional stuff and that is this Online Book about the boat. I say better because the key to selling this boat is communicating to a potential buyer the benefits of buying her, and that can’t be communicated quickly because so much preliminary education needs to be done first.

      In other words, all of our marketing and sales efforts need to funnel to one thing, reading about the boat. After people do that, they will either “get it” or they won’t. And as at this morning 154 people “get it”.

      • John Jun 3, 2014, 8:08 am

        Oops, just took another look, make that 155!

      • Marc Dacey Jun 16, 2014, 11:45 am

        John, if it’s any comfort (not that I think you need it on such a well-conceived project), I bought my first boat with money made from marketing, and I think you are spot-on with your instincts to keep away from the glossy stuff. I would suggest, however, that if you take up the offers of boat-show booth runners to get the word out (which is a logical and economical choice) that maybe you blow $10 and get 500 business cards made up at Kinko’s with two things: the line drawing of the the A40 on one side and a URL with “” (or whatever simple URL you want) on the other. In red. It’s so minimal and counterintuitive an idea to give out BUSINESS CARDS in 2014 as to be memorable. And, lest we forget, cheap. If you wanted to track results, you could also print a QR code on one side, as long as that didn’t bust the “pint-and-a-half-pint” marketing budget. So there’s your Monday morning freebie.

  • George M Jun 2, 2014, 6:14 am

    Very nice! Good job Erik.

    Moderation in every way and a lovely balanced hull that shouldn’t change too much in her geometry as she heels.

    Just a couple of thoughts.

    1. She has a very deep, some might even say extremely deep, forefoot. In the perspective this makes her bow look a little pinched to my eye. Indeed, the v is quite extreme all the way back to about the 10th section. What is the rationale behind this choice? Wont this detract from the balance in the hull as she heels? Wont it produce a tendency to bow steer when heavily pressed by following seas? Does the v need to be this extreme to prevent pounding to windward?

    2. 8 tons lightship was pretty light for a 40ft serious cruiser, its getting on for down right racy for a 11.6m lwl serious cruiser. If she has 800kg of diesel and fresh water tankage, and then about 1 ton of cruising stores, food etc, then her loaded displacement with 2 crew is going to be about 10 tons. I.e., in cruising trim she will be 25% heavier than her lightship displacement. Due to the soft turn in her bilge (a definite plus in my view) she will sit substantially lower in the water than the line drawings suggest.
    Where’s the loaded displacement waterline? Wont such a large change in displacement from lightship to cruising trim detract from her average performance? For example, my eye suggests to me that when loaded her transom will be just kissing the water when stationary, which means that she will start dragging it when sailing and motoring.

    If the waterline in the drawings is the 10 ton displacement line, then this second concern is mute as she sits beautifully on that line, but if this is the lightship line, then I am concerned that she will suffer from overloading.

    A bit more flare at the root of the keel to spread grounding loads would be nice.

    Also, I wouldn’t both with a fused rudder. Its so much shallower than the keel that it isn’t at much risk, and from experience there is almost always some movement in the rudder on the pivot when sailing with these kinds of rudders, that gives rise to small jarring jerks in the hand on the tiller that detract from the pleasure of sailing.

    Again though, nice to see a yacht designed from the outside in for once.

    • pat synge Jun 2, 2014, 7:51 am

      Re: ‘fused rudder’.
      Surely any annoying slop can be eliminate quite easily with sacrificial bolts clamping the cheeks together while still providing a valuable safety factor if you run over a floating log or similar .

      Re: flare at the root of the keel.
      Cast iron or lead keel? Many cast iron (or steel) keels have a flange embedded flush into the bottom of the hull which increases the surface area and through which the keel bolts pass which makes them extremely easy to inspect and/or replace.
      Bronze is great but expensive. High tensile steel is inexpensive and readily available just about anywhere. The epoxy bond + a FRP laminate over the flange should do most of the job anyway and the bolts are only there for abnormal extreme loadings. Given a good coating of epoxy when fitted HT bolts should be good for decades.

      • Laurent Jun 2, 2014, 9:06 am

        I think that the best “affordable” solution today is a slightly recessed box in the bottom of the hull (2 or 3 cm.), a wide flange atop the molten iron keel that gets inside this box, two rows of iron (“ultra low carbon steel”…) bolts, one on each side of the flange and no glue or composite lamination below the keel flange to allow keel disassembly for repair. User who want bronze bolt can easily put them in place afterward as a replacement of iron ones

      • John Jun 2, 2014, 9:26 am

        Hi Pat and Laurent,

        We are getting ahead of ourselves here. While I would like to see a lead keel, Erik has not done the detailed engineering on the boat yet. The idea over the next three posts is to expose the preliminary design to everyone, and then Erik will do the final engineering.

      • George M Jun 2, 2014, 2:00 pm

        Pat, that is an excellent point. I was envisaging a keel bolted flush to the hull but I have seen what you are talking about where the keel sits embedded into a slot in the hull. There are pros and cons to each. With the slot there is no need of flare in the top of the keel and the bolts are of far less importance. You bolt side to side through the top of the keel inside the hull, so the bolts are under pure shear load and not under tension or compression on grounding. In such circumstances it may well be that crevice corrosion is not such an issue so you can get by with more standard bolts. Also the bolts are very easy to change out with such a keel. Hell, its about 1 hrs work to change them all out, so you could do it every year if you wanted to.

        The big minus of this way of attaching the keel is that you cant have a bilge sump.

        For my part structural integrity is more important than a dry bilge, but for some people a sump is a must have item.

        But anyway it certainly is something to consider.

        • George M Jun 2, 2014, 2:10 pm

          Just read the later comments, so sorry for feeding the keel fire above.

          • John Jun 2, 2014, 4:57 pm

            Not To worry George, I didn’t handle things terribly well. See my last comment at the bottom of the post.

    • John Jun 2, 2014, 5:53 pm

      Hi George,

      The reason for the deep forefoot is to prevent slamming upwind. She probably looks a little “pinched” to you because you are used to seeing boats that carry their beam further toward the ends (higher prismatic coefficient) to increase volume for a given length. Or to put it another way, this boat would be about 38-feet, or maybe less, if we let the marketing guys get to her. By going to 42 at the same displacement we are adding upwind ability and speed and we can make the bow much finer and still have it balance to the stern. The bow is, as you say, fine, but there is plenty of buoyancy further aft, but forward of the keel. (What Pat was worried about.)

      The hull volume is actually quite symmetrical fore and aft, and, as I said in the post, healing will have very little effect, because the stern balances the bow nicely. Also, as I said in the post, Erik has checked this hull very carefully at all reasonable heal angles to make sure that there will not be steering problems. He will do further work in that area in the final design phase and then another NA will check all his numbers.

      As to bow steering. I don’t think she will do that. There are a lot of things that contribute to bow steering other than a deep V’d forefoot. One is a wide stern because when the boat heals on a wave face the bow is driven down. We don’t have that problem. Also there is quite a lot of flair in the forward area, which provides reserve buoyancy, which again prevents bow-steering. (I know this works because my own boat works this way.)

      Weight: Yup, she’s a small boat by todays standards. No getting around it. We make here heavier, she gets more expensive, quickly too.

      I have written about that here.

      Maybe one day there will be a big sister at say 25,000 pounds (about the weight of a Valiant 40) but that boat would be a (I’m guessing here) Adventure 48-50 and cost around $350,000, at least. (At this size range gear prices increases, as the boat gets heavier and more stable, are exponential, not linear.)

      Load carrying: And Erik has specified a payload of two tons which will be plenty for two people full time cruising with modest needs. If you want to carry more than that, well you need a bigger and more expensive boat. There is simply no getting around it.

      You certainly don’t need 800kg of tankage to fulfil her mission 500kg should be plenty. Yes, if you want to cram in everything that the yachting magazines tell you these days that you need to go cruising, she is too small a boat for you. But if you go back to a simpler time, say the 1970s, she would be considered a big luxury boat. It’s all about where one sets ones expectations.

      The waterline is light ship. And you are right, the transom will immerse when fully loaded, and that’s a good thing, as Martha Stewart would say. The reason why goes back to what I was explaining in the post about optimizing for slow speeds or fast speeds. In the former case an immersed transom slows you down, but at fast speeds, when done right, as Erik has, it increases the effective length of the boat and makes you faster and gives you better steering.

      As I said in the post, it was Steve Dashew that knocked that into my thick scull, so I have it on good authority. Look at all his boats, sail and power, they all immerse their transoms when loaded.

      One other thing, I think I’m right in saying that it is water plane area and hull flair above the light ship waterline that governs weight required to immerse a given amount, not shape of the bilge sections.

      • RDE (Richard Elder) Jun 7, 2014, 10:22 am

        Hi John & Eric,
        re immersed transom:

        Look at the current modifications to Wind Horse. Steve comments that the wake is much cleaner and the boat more efficient after adding a stern addition (ie eliminating the dragging transom).

        I for one would like a bigger and more secure place to stand on the A40 when I’m trying to convince a big bull Mahi to come aboard! And an extra 6″ of sugar scoop would balance the lines better when viewed in side profile at virtually no cost.

        • C. Dan Jun 7, 2014, 10:35 am

          Keep in mind that as currently designed the “sugar scoop” is divided by the slot for the rudder, so I’m not sure the extra 6″ will really add that much utility in terms of lounge space / fishing platform.

          Whether it would eliminate drag is another issue entirely…

        • John Jun 7, 2014, 12:00 pm

          Hi Richard,

          I Just took a look at a pic of WH that I took after they added swim platform and it is still immersed. In fact in our long phone call on the subject Steve told me that transom immersion (at rest) is actually something the that improves high speed performance (when done right) because it increases apparent waterline length—fools the water into thinking the boat is longer than she is and moves the stern wave back. The only time it hurts you is at very low speed to length ratios.

          • RDE (Richard Elder) Jun 7, 2014, 3:47 pm

            Hi John,
            I wasn’t able to find a photo that showed the Wind Horse transom extension as clearly as yours. I suspect there is a trade off that is related to relative speed through the water just like you say. And the Dashew boats are so long that 9 knots is more like -4 on a 40 footer.

            I’d still like a larger place to land my big fish!

          • John Jun 7, 2014, 4:36 pm

            Hi Richard,

            I think you are about bang on: the immersed transom will start to hurt a bit at below about 4 knots, but them most of us are motoring by then and anyway Steve tells me it’s only about a 5% hit.

            Still Erik will be playing with all this in his velocity prediction program as part of the final design tweaks. I will tell him about your fish killing platform!

  • John Cobb Jun 2, 2014, 9:10 am

    Without compromising copyright or proprietary issues would it be possible to make some of these drawings available in a file format that we could import into something like Sketchup?

    • John Jun 2, 2014, 9:23 am

      Hi John,

      Interesting idea, but I think I would rather not. Erik is a professional Naval Architect and sailor with probably 150,000 miles experience. As such he is really qualified to handle the design aspects. Further, the design is not yet final, and further still, the final design will be reviewed by another professional yacht designer. Given that, having a bunch of other people, mostly unqualified, all trying to get their ideas incorporated, would be a huge distraction and we might end up with camel (horse designed by a committee).

      Having said that, we are perfectly happy, and actively soliciting, overall ideas, but we don’t want a bunch of people trying to tweak the details.

      • John Cobb Jun 2, 2014, 10:40 am

        I understand.

  • John Jun 2, 2014, 9:39 am

    Hi All,

    Several people have brought up engineering issues like the keel to hull joint. Erik has full on engineering training and designs commercial vessels like pilot boats, as well as yachts, where failure is not an option.

    In addition the final design and engineering will be checked by another professional (standard practice in the commercial world). Finally, Erik has already committed to testing the prototype with a full speed grounding, among other things.

    Given that, I really don’t want to get into a lot of detailed discussion, particularly at this point, on the construction. Let’s leave that to the pros and concentrate on what we want the boat to do including any testing we would like to see.

    • John Jun 2, 2014, 1:11 pm

      Hi All,

      In rereading my comment above, and based on a note I got from an old friend and reader, I think I may have taken a bit of a wrong tack (tacked on the lift) here.

      My intent was, and is, not to stifle suggestions. My worry was that we would get into a long argument about say, lead or steel for the keel (I favour lead) and lose touch with what this post is about: the hull form.

      So, if you have suggestion about construction that you wish to air now, please go ahead. Having said that, I may not engage with them because, as I said, we are a long way from making those decisions.

      One other thing, know that Erik reads and/or re-reads all comments relevant to what he is about to work on, before taking each step in the design.

      Having said all that, it is important that I make clear that we are not crowd sourcing a design here. If you think a camel is a horse designed by a committee, imagine what a crowd sourced horse would be! The design is all Erik and he makes the final calls. Even I am only an advisor to Erik.

      Having said that Erik is incredibly open to suggestions, so, by all means suggest away.

  • ben Jun 2, 2014, 10:55 am

    Inspirational stuff John! and kudos to Erik for his ability to stay focused on the design too. I’ll be watching closely and can’t wait to see this in more detail!

    …I didn’t know that I wasn’t supposed to beat into St. Georges without local knowledge! Did that in ’98 on a 37′, heavy wooden Carol (Stretched Tahiti) ketch… after almost exactly the scenario you laid out for the “modern fat sterned” vessel. On a (poorly planned) November passage from Halifax, overtaken by a cold front, knocked down more than once by the lovely square waves in the gulf stream, shallow bilges, water in electrics, no engine. On our good old beast though, the hatches didn’t leak and she didn’t flex – it was the water tanks that failed and flooded the place! D’oh. anyway, in the end we beat our way in thru the cut with ragged sails, watching carefully from the bow and tacking when we saw the coral looming up. A high-tension end to a passage I’ll never forget.

    I sure would have liked to have been able to beat to windward. We simply couldn’t, and took a real pasting as a result… more than once. The A40 looks like a much better boat for this task – which is NOT uncommon if you cruise outside tradewind routes!

    • John Jun 2, 2014, 5:02 pm

      Hi Ben,

      Thanks for the backup on my daydream. As you point out, not really a dream, more an all to frequent reality.

  • Brandon Ford Jun 3, 2014, 12:54 am

    Hi John,

    I’ve followed with great interest the Adventure 40 project. Bravo to you and your crew for moving it forward to reality. Best of luck.

    I was excited to see the specs, lines and dimensions of the Adventure 42. She very closely matches my own boat, a 1971 Columbia 43: LOA, 43; Beam, 12; LWL 33, and 18,900 pounds displacement. We bought it as a project boat. The previous owner put in four years of hard labor in which he cut out the fiberglass interior and tabbed and taped in new bulkheads and furniture. He also rebuilt the Perkins 4-107. His work was of the highest quality, but when he got cancer he had to sell the boat. I have had to redo very few things that he did. Getting rid of the fiberglass liner (which just floated around in the hull of the old Columbias) got rid of a lot of weight and the new bulkheads, furniture and stringers added a lot of strength and stiffness. He also fiberglassed all around the inside of the hull-to-deck joint, which often leaks when the boat is pushed hard to windward.

    My wife and I have been working hard for almost two years finishing the project and plan on leaving for a two year, or more, cruise in September.

    I wish the Adventure 42 was finished and we had the money to buy and outfit her and still go cruising. That’s just not our reality. We will have about $45,000 in the boat when we leave. It’s paid for. All plumbing, electrical wiring, batteries, refrigeration, Hydrovane, and much of the other gear etc. will be new. I feel pretty confident in the boat and it’s design. I also know her inside and out.

    Best of all, this project has been about the most fun my wife an I have ever had with our clothing on. She is just as committed as I am. She does most of the painting and varnishing and all the sewing, including a new dodger, bimini, 15 cushions, pillows, the list goes on and on.

    I know you don’t recommend most people doing this, and I agree with you, but for my wife and me it has worked out well … so far. It’s pushed our skills to the limit but so far we’ve been able to do every project and stay on schedule. We got the boat just at the right moment in our lives and in the rebuild of the boat. The previous owner did most of the hard, nasty work and we’ve had a ball turning the boat into our own. It has the colors, fabrics, woods, etc. that we like and the woodwork is the best I can do — and I’ve been building furniture and small boats for 20 years.

    What I’m grateful for is your experience with anchor selection, batteries and so on there on your site. I’m a member and count it as a very good value. The information is excellent.

    Brandon and Virginia Ford
    SV Oceanus
    Newport, Ore.

    • John Jun 3, 2014, 7:50 am

      Hi Brandon,

      Great that this is working out for you and you two will get to realize your cruising dream. One thing your story does bring out that should not be missed by those looking to copy you is that, as you say, your refit leveraged the work of the previous owner of the boat. One does have to wonder what the hours and money invested would be if one added his investment in both to that of you and your wife. And that leads to the the key take away for me in your excellent comment: don’t even think about a refit unless you know you will actually enjoy the work involved and that your spouse will do likewise—the journey must be the reward.

      • Brandon Jun 3, 2014, 10:01 am

        So right John. This was his second rebuild of a cruising boat, so he knew what he was doing. He confided in me that his investment in the boat was about $25,ooo more than we paid for it. The used boat market is really in the dumper and project boats are almost impossible to sell.


  • George M Jun 3, 2014, 4:28 am

    Hi John,

    Thanks for explaining the deep forefoot. It makes sense now. I could see that the hull would be well balanced I was just thinking that without such a deep and pointy bow she would be even more so. I also see that the keel and rudder are pretty far aft (I presume she is to be cutter rigged then?) and that, together with the narrower aft sections, will probably more than counter any tendency to dig her bows in.

    With respect to your explanation of the displacement, I agree with Erik’s design criteria of 2 tons load, that is my estimate also. A careful couple might get away with 1-1.5 tons, but cruisers aren’t all that careful. I also agree that this is not a boat for those who want all the comfort and convenience of home on the water; my concern we just that she would carry the necessary cruising paraphernalia for a couple and I reckoned that at no more than 2 tons.

    By “soft turn to her bilge” I meant the nicely round, almost half circle, sections Erik has drawn. These minimise wetted surface and give the boat a soft motion as she heels to wind and waves, a balanced waterplane as she heels and a lower prismatic coeff. Most modern yachts have a tight turn, and even chines, from the hull bottom to the topsides to maximise form stability. The sales argument being that people new to sailing like to sail flat and have maximum interior value. I say: If that’s your cup of tea then buy a multihull. Anyway, a byproduct of square sections is that the boats static(!!!) water line doesn’t change much as you load her. With more circular or wineglass sections the change is static water line with additional weight is greater.

    Anyway I had thought to preempt your response by asking if Dashew’s comments about maximizing sailing performance for heavier airs and putting up with a little inefficiency in light airs was behind the choice, but decided against it. I see the rationale and think it is a good one. She will fair fly though. I make her loaded waterline 40ft roughly, which gives her a dwl ratio of 156!!!. That is fully loaded for cruising!
    That’s Dehler 41 territory or better. Your average serious cruiser is usually around 230-250 lightship. Her first test report should make interesting reading.


    • John Jun 3, 2014, 7:44 am

      Hi George,

      I agree entirely on your comments about bilge rounding, although I do think she will stiffen up nicely at about 15-20 degrees of heal, much as out own boat does. My only reason for mentioning that was that I don’t think that has any effect of the amount of additional weight over and above light ship that it takes to push the hull down a given amount.

      And you are, I think, absolutely right, she is going to be a flyer with her long waterline. In fact, I fear that she will even give our own “Morgan’s Cloud” a run for her money in the right conditions. While she was not designed to be a racer per sec, it will be a lot of fun to take her out at ones local club and watch everyones faces when the “cruising boat” slaughters many more racy looking boats. Of course I wouldn’t count on winning a lot of sliver because any PHRF handicapper worth his salt (I used to be one) will see through the cruising look and slap a pretty low number on her.

      • George M Jun 3, 2014, 11:38 am

        Hi John

        You still get the satisfaction of seeing the consternation of the fully crewed racing boats as they struggle to put you under their lee though, even if you don’t win on corrected time. I remember that feeling well from when I had my little IF-boat.


        • John Jun 3, 2014, 6:08 pm

          Yup, going fast is always fun! Bill Lee was right.

          • George M Jun 4, 2014, 6:31 am

            With a lightship dwl ratio of about 145 and theoretical hull speed of 8.3kn, she will certainly be fast.

  • Eric Klem Jun 3, 2014, 9:33 am

    Hi John,

    The preliminary design looks very reasonable and seems like it should hit the spec well. It was interesting to read the discussion of the deep forefoot above, this boat definitely has a deep one but many of the boats that I like do have a deep forefoot.

    This may be getting ahead of things because you haven’t released any information on the interior but do you know where you expect the shaft to come through and where the prop would sit?

    I am curious to hear your thoughts on rolling both while sailing and anchored. In general, the sections are pretty rounded and the boat is on the narrower side so I would assume that Erik has given some thought to this.

    Thank you both for pushing this along.


    • George M Jun 3, 2014, 11:19 am

      Hi Eric,

      My tupence worth on the sailing side is that I’d rather have some smooth rolling while sailing downwind than the rather abrupt motion one gets with modern AWB’s with squarish sections aft. Also, if the motion bothers you then you can always sail angles downwind. On the anchoring side, I don’t mind rolling at anchor—I quite like being rocked to sleep like that—but I understand that I might be in the minority here. Anyway, so far as sacrifices go, that is one I could live with I think.


      • John Jun 3, 2014, 6:00 pm

        Hi George,

        That makes sense. I think with her long waterline length and generally slippery hull, sailing pretty hot angles down wind is going to make a lot of sense.

    • John Jun 3, 2014, 5:54 pm

      Hi Eric,

      You can see the shaft exit on an earlier rev level of the design on this post. The boat got a bit longer, but that shaft position has not changed appreciably. As you can see, plenty of room to get a lifting sling aft of the keel without any danger of bending the shaft.

      The rolling question is an interesting one. I have a pretty good feel because our own boat is pretty rounded too, in fact a bit more so. But I’m afraid it’s all empirical based on that, and observation, because my theory in this area is pretty sketchy. I guess there are three answers:

      • When sailing or motor-sailing: Not a problem and I think the motion will be actually more comfortable, overall, than a harder chined wider boat. After all you don’t roll much with sail up, and bad pitching and slamming is way worse than a bit of roll. Win for the A40.
      • When motoring in flat calm with no sail up: She will, I’m guessing roll more deeply that some wider boats, but I think I’m right (you would know better than I) that roll period won’t be negatively affected and it should be pretty soft and not snappy? …Yes, I think that’s right since you only have to look at the snappy roll that cats have in a bad sea with no sail. I have to say I’m a bit hazy on the theory here, but I do know that we have motored for thousands of hours in calms in the Arctic on our boat and never found the roll to be a big problem. Yes, you have to get used to it, but it’s not the depth of roll that makes life uncomfortable, its how snappy it is.
      • At anchor in a rolly anchorage: Hum, I just don’t know. Having spent quite a bit of time in such anchorages in the Windward islands, it seems like most all monohulls roll about the same. It’s Cats that have the big advantage here…but then I guess if a cat is better, then a very wide hard chine boat is going to be less rolly that the A40 in this case. Let’s call that one a win for the wider boat.

      Well, that’s the best I can do on this one. I will pass it on to Erik for a smarter, I’m sure, answer. May take a few days in that he is on his way to Greenland.

      • pat synge Jun 3, 2014, 10:36 pm

        I’m going off topic a bit here but this may be of interest as it relates to rolling at anchor.

        When working in New Caledonia I was asked to help reduce the roll of a particular design of fishing boat. The guys didn’t mind it rolling when underway but it made life on board difficult and unpleasant when line fishing at mooring.

        Very efficient and simple to use as they don’t need spreaders. Simply hang one over each side and the roll pretty well stops immediately. The flaps were made of old conveyor belt (there’s lots of that in NC!). Obviously one hangs a weight off them when in use. Sleep well!

        • John Jun 4, 2014, 7:26 am

          Hi Pat,

          Looks like a great gadget, and easy to make too. Thanks.

      • Eric Klem Jun 4, 2014, 10:06 am

        Hi John,

        Thank you for the response. My feeling which seems to agree with yours is that rolling won’t be an issue when underway except possibly when motoring with no sails up. Originally, I was only going to ask about rolling at anchor but I figured what the heck, I would ask about the whole thing. I do have to say that there are some monohulls that roll much more at anchor than others. I would guess that we spend ~20% of our time anchored in places with a significant amount of roll and some boats seem to get going and never stop. They seem to be the equivalent of a car with good springs but not dampers (shock absorbers) which has just gone over a bump.

        One good thing about the deep forefoot is that it should help keep the boat from sailing at anchor although it may make things a bit worse if there is a lot of current.


    • Erik de Jong Jun 8, 2014, 5:08 pm

      Hi Eric
      From a physics perspective, rolling and pitching are very similar. As most sailors know, weight in the ends of the boat is causing and increasing pitching. The same counts for rolling. Heavy objects in the sides cause and increase rolling.
      What fewer sailors know, is that volume has a similar effect on both pitching and rolling as weight does. Submerged volume has a negative weight equal to the amount of water it is displacing.

      This basically means that the boat with the least volume,and with the least weights near the chine, is the least prone to rolling, regardless if it is sailing or at anchorage.

      Another way to visualize this, is not thinking of a wave as a sine shaped piece of water, but as an inclined surface. The boat with the wider waterline, or stronger chine if you’d like, will immediately try to follow the surface inclination. Where as the boat that would be a perfect sphere, would not even move since the waterline shape and underwater volume remain identical.

      According to this theory, a catamaran would roll more than a mono hull, and that is usually not true on an anchorage. This is solely because the wave length and or height is seldom enough to lift one hull more than the other. At sea, on the other hand, cats can roll quite a bit worse under certain conditions.

      So to answer Eric’s question in one short sentence: the A40 will roll less compared to boats with wider sterns and stronger chines.

      [Answer from Erik on “Bagheera” in the Labrador Sea on the way to Greenland. Via satellite email and John.]

      • Eric Klem Jun 8, 2014, 8:06 pm


        Thank you for the explanation and it sounds like this should not be an issue. You’ve got my curiosity going now and it sounds like I have some reading and thinking to do. I did manage to largely solve a rolling issue on a previous boat by some basic weight redistribution about the roll axis but it has made me very cautious since then as it was pretty miserable.


      • Emilios P. Jun 9, 2014, 9:17 am

        Hi Eric,
        would I be correct in understanding that the hull shape (very wide beam, sharp turn/chines) that provides for a lot of form stability would also cause a lot of rolling at anchor or under way ?
        Kind of a reverse effect, what keeps a boat “upright” will also make her roll ?
        Is it also correct that a very wide beam also lifts some of a fin keel out of the water when heeling (the boat rests on her side) thus reducing its efficiency ? which is why some recent french designs have twin fin keels off centre ?
        Please enlighten me.

      • RDE Jun 10, 2014, 1:23 am

        Hi Eric,
        I’d have to add that there are other factors at work in dynamic rolling in addition to relative beam, chine, and roundness or flatness of hull form. For example, a full keel’s surface area will have a greater hydrodynamic dampening effect than a high aspect racing blade keel. At the same time the full keel boat will have a higher center of gravity than the deep draft racing style keel, which works in the opposite direction to enhance rolling. The extreme case would be a round bottom hull with the center of gravity and the center of buoyancy at the same point, (near zero form stability and ballast lever arm) which would take little more than stepping aboard on the rail to initiate rolling. A wave passing under it might cause less initial motion than on a beamy chine boat, but the effect will be far more exaggerated.

        And contrary to what one might think, putting a megabucks carbon mast on an old slack bilged full keel boat will exaggerate or quicken its roll motion rather than reduce it. The weight aloft of the wood or heavy aluminum spar serves to dampen the initiation of rolling in the phase of the roll before ballast stability begins to become effective, thus making for a more comfortable motion than the lighter mast on this particular kind of hull.

        As is the case in so many fluid dynamic situations, the equations that accurately describe motions are not simple.

        • Laurent Jun 10, 2014, 10:13 am

          At first glance, boat roll and pitch in steady sea and boat movements are simple mechanical resonance problems corresponding to equations of the type :
          Couple = J * alpha” (J being the boat moment of inertia and alpha” the second derivative of the roll angle) and Couple = A * alpha + B, which gives something like : A * alpha + B – J * alpha” = 0 (classic differential equation for mechanical systems subjects to resonance…).

          If roll is excessive, first idea is to alter the J value, increasing or decreasing it to set natural resonance frequency further from excitation signal frequency (here : waves frequency…). In case of roll it means decreasing or increasing lateral weights repartition (in case of pitch, it means altering longitudinal wight repartition).

          Looking a bit further, we see that the real equation corresponding to a given hull in a given sea is very complex, because the couple generated by boat hull angle in a sinusoidal wave patern is not a sinusoidal function of the angle ( it get influenced by precise hull form and dynamic wave interactions with hull) and because real wave patterns are not sinusoidal (more like combination of sinusoidal frequencies…).

          I understand that the lateral and longitudinal immersed-volume vs. hull -angle functions have impacts on roll & pitch (better if they are not too much continuous…), and that a not-too-round master section contributes to dissipating roll energy, but current practice for ship roll & pitch design-optimisation generally uses model testing as much, or more than calculus, and those model testings can be very expensive….

  • Bill Attwood Jun 4, 2014, 2:58 am

    In spite of the enthusiastic comment above, I confess to being a bit disappointed with the initial design. The bow sections are rather hollow, and should an unprotected rudder have a place on an offshore crusing boat? The comment that fitting a “fuse” would minimise the effects of a collision seems to be tacit acceptance that this type of rudder isn´t ideal. Would the increase in wetted surface of a skeg really have that much effect on performance – presumably only in light airs anyway? Although it may be too early to make judgements about the keel, this is also an area where I have concerns. I´m not an engineer, but the chord (I hope that this is the correct term for the cross section) at the keel root looks not dissimilar to that which has caused problems on so many current designs. The distribution of weight at the bottom of the keel only increases the problem. The bilge is also very flat without any sump, any water coming aboard will soak the lockers both sides as the boat rolls. Could it be that comfort and safety is being, to some small degree, sacrificed to the “need for speed”? On a positive note, I very much like the idea of a transom-hung rudder, and the clever idea of mounting it in a slot in the transom. Sorry for the negative comments.

    • George M Jun 4, 2014, 6:00 am

      HI Bill,

      While I initially shared your concern about the bow I think John’s explanation of the rationale behind it at least makes this design choice defensible. I too am also concerned about the keel root geometry, but I think that can be addressed either by flaring the root of the keel or by embedding the keel into a slot in the hull. If the keel root is flared then a small sump box could be incorporated to address your concern there; however, if the slot keel is preferred to maximize the endplate effect then one will just have to live with bilge water sloshing around and work hard to have the driest bilges possible.

      However, I feel that I have to come to the defense of the decision to be skegless.

      One of the nice things about a transom hung rudder is that one can optimise the rudder for maximum efficiency without worrying about incorporating a rudder stock. I.e., with a transom hung rudder you can get a 12% thickness ratio on a NACA 63 foil, which is almost impossible to do with a standard spade rudder. This enables the rudder to be smaller and so reduces the steering loads allowing a large boat to be tiller steered and helping any autopilots you might have. Putting a skeg of similar width in front of such a blade wont add much in the way of protection or structural integrity because the skeg will have to be pretty narrow and flimsy.

      Furthermore, with a full depth skeg you wont be able to semi-balance the rudder. That might be fine on a 30ft boat or on larger boats with powerful wheel steering, but you need to semi-balance a tiller controlled rudder on a 42ft boat if you want to keep tiller length the right side of 2m.

      And finally, cracking at the root of the skeg is one of the most common problems faced by cruisers with this type of arrangement. I know that you can build your way out of that problem, but that just adds weight in the wrong place.

      If however, your concern is directional stability, then to my mind it makes more sense to have small fin enclosing the drive shaft and to rely on that for feathering the hull.

      So if it is a choice between a skeg and fuse to protect the rudder on this type of boat then I’m afraid that I would have to go with fuse every time. Though, to be honest, I just don’t see the need for protection of any kind considering how much shallower the rudder is than the keel on the A40. Perhaps a fused rudder would be useful for clearing weed and lines off the rudder, particularly if its semi-balanced, but is that really worth the extra expense?

      • John Jun 4, 2014, 7:31 am

        Hi George,

        I couldn’t have said it better myself. In fact, I doubt I could have said it as well. Thanks

    • John Jun 4, 2014, 7:39 am

      Hi Bill,

      Sorry you feel that way. I used to feel that all cruising boat rudders should have a skeg too, but in recent years have decided that’s not the case. George does a great job of explaining why.

      As to water sloshing around. Please don’t worry about that. Erik and I have discussed that at length and we have a good solution that will be built in as part of the keel reinforcing. Talking of which, this keel has a great deal more root area fore and aft than the keels that have been causing problems, probably better than double. And, this is a preliminary line drawing so you are not seeing what will be done to make it massively strong.

      Erik is designing the keel to withstand multiple groundings at hull speed (~7.5 knots) without structural damage and the prototype will actually be subjected to that testing.

  • Bill Attwood Jun 4, 2014, 7:52 am

    Hi George. I enjoyed your interesting and informative reply. I own a long-keeled Rustler 36 with transom-hung rudder and tiller steering (converted from wheel steering), which obviously colours my view of hull design. I shall not be in the market for an A40 (too old and too much time and money invested in refitting the Rustler), but it is a fantastic project which deserves to be a great success. I was particularly interested by your suggestion of a small skeg protecting the prop, which would also give directional stability – a very nice idea.
    Yours aye,

    • George M Jun 4, 2014, 10:13 am

      Rustler 36 is a beautiful boat. Its actually related in hull design to my first boat International folkboat. They are quick for longkeelers, and their motion in a seaway is just so smooth. But the rudders on these boats are big and completely unbalanced. The folkboat was a bit heavy to steer so the Rustler must be even more so. Definitely as large as you should go with unbalanced tiller steering. That said they track like they are on rails and a heavy helm is forgivable in a boat that loves to sail in straight lines, so I still would have changed to tiller steering as you have done. Beautiful boats, and I am deeply jealous at your good fortune in owning one.

  • Emilios P. Jun 4, 2014, 9:48 am

    Hi all,
    On keel attachment :
    1) the common way where keel root fits flush with the hull bottom, keel held by bolts and backing plate (rather than largish washers as seen on some mass production yachts),
    2) a “box” inside the hull where keel root fits just and keel bolts are then horizontal only taking the weight of the keel, other stesses taken by said box, and
    3) a “box” outside the hull with keel bolts vertical (and backing plate) but with a “step” facing forward so that any stresses from grounding are taken by the step in the box. This also provides for a nice deep sump.
    None of the above is my original idea and I am sure Eric is aware of them, just as examples…
    Cases 2 & 3 have been used but I suspect are more expensive to manufacture.
    Sorry, I am useless at drawing…

    • John Jun 4, 2014, 4:13 pm

      Hi Emilios,

      All sound like good ideas. I’m not engaging on keel engineering right now for two reasons: I’m not qualified to do so, not having any engineering training, and Erik, who does, is it sea, so not available. Rest assured that it will be both strong and tested, as I have said in other comments.

  • Enno Jun 5, 2014, 9:42 am

    I’m not a naval architect so my thoughts might be stupid – but I could actually imagine some positive effect of a narrow deep bow on the interior layout.
    If one has a bow like this I would imagine that one needs to move the forward cabin aft to get enough space for the feet of two people to sleep well. If one does this, would it be possible to gain enough space for a sail locker between cabin and chain locker? If one makes this only accessible from the foredeck one would also get an extra watertight compartment which might come handy in case of a collision. A space like this would also provide a dry space for the windlass motor (some of these don’t like salt water).
    On my current boat which is 31ft I’m not lacking living space but storage space. That’s probably typical for modern designs.

    • John Jun 5, 2014, 12:40 pm

      Hi Enno,

      Your thoughts are not even slightly stupid, in fact they are very smart. Part of the reason the boat got longer was that we were running into exactly the issues you mention.

      The bottom line is that, contrary to modern trends, it’s actually way easier to do a good layout in a long thin boat than in a short fat one of the same displacement. And you are so right about storage.

  • Dick Stevenson Jun 5, 2014, 4:39 pm

    John, I suspect you feel quite chuffed and a bit humbled by the quality of the comments on your site. I know I am impressed and quite appreciative.
    Dick Stevenson, s/v Alchemy, Lerwick, The Shetland Islands

    • John Jun 5, 2014, 5:54 pm

      HI Dick,

      You are absolutely right on both counts.

  • Mark Jun 5, 2014, 9:28 pm

    It is very interesting watching this design come to fruition. I have a old Cal 48 which I restored that has the same 12′ beam but only a 35′ waterline. It also has an encapsulated keel. Long narrow boats have nice proportions that do attract attention when out at an anchorage. They are alot more fun to sail. It looks like this will be an attractive boat.