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.

185 comments… add one
  • Bill Attwood Jul 25, 2014, 3:17 pm

    Hi John.
    I find it difficult to understand the insistence on a below deck autopilot, and wonder if the people who are such strong advocates for them have tried the alternative. I sail a Rustler 36, a long-keeled 1980´s design from Holman and Pye. I have converted from wheel to tiller steering – Rustler Yachts still offer both options. My steering systems consist in: Windpilot Pacific; small Tillerpilot rigged in place of vane when necessary for coastal sailing or under motor; large Tillerpilot connected direct to tiller for rough conditions when for any reason the Windpilot cannot be used – I see this mainly as a back-up for the Windpilot if it becomes non-operational. The large tillerpilot has only the ram mounted in the cockpit, with all electronics and fluxgate compass mounted below decks.
    The price of the small Tillerpilots is such that one could easily buy a spare as back-up. I have used all these systems extensively and can report that they function really well. If they can work for a Rustler, then they should find the A40 no problem. I would welcome a summary of the pros and cons of a below-deck autopilot from the advocates, particularly the con (as I see it) of a system which is hard to get at and therefore won´t be properly checked and maintained.
    Yours aye,

    • John Jul 26, 2014, 9:09 am

      Hi Bill,

      That all makes sense to me.

      To answer your question about the pro of an under deck autopilot, on a boat under about 12 metric tons it is purely a convenience item when measured against a vane gear. I think they have become as popular as they are because they, to a large extent, obviate the need to really understand how to balance the boat properly with the sails, a requirement when using a vane gear—no fiddling around, just push the on button.

      On boats over about 20 metric tons I think said pilots become more a need. We have one on our boat and would not be without it, but she is 22 metric tons light ship and really on the upper end of the loads that are practical for a vane gear. Having said that we have a vane gear and it has sailed us for many thousands of miles, including a tran-Atlantic.

      On the cons side of underdeck autopilots, I think what people miss is real expense of one. A good one, well installed, is going to run >US$5000, and as much as $10,000 if all the work is done by a yard. But that’s just the start. These things are power hogs and there is no practical way to feed them using solar and/or wind power. So that means a diesel and/or hydro generator, unless you are willing to run the main engine for several hours a day to charge. Doing a full underdeck autopilot and the support systems properly can easily run you US$15,000-20,0000. That 5%-10% of the cost of the A40…for a convenience item!

  • RDE Jul 26, 2014, 9:57 am

    Hey guys,
    Let’s think just a little bit outside of the box.

    1- Below deck autopilot installations need cost $15-20,000? Certainly if they are the usual suspects we are familiar with—power hungry machines necessary to control a large boat like MC.

    On the other had, the Cape Horn wind vane was designed for exactly that purpose. Below decks addition of a small tiller pilot for use while motoring. Because it drives the servo rudder which in turn provides the steering force it uses almost no power. Here is a photo (third one down) of just such an installation.

    Combine the Cape Horn with a Raymarine Evolution ( with tiller pilot ram for little more than $1,000 and you have a low power draw electric autopilot with relatively sophisticated electronics, remote control, and all components mounted in weather protected locations.

    2- “Transom mounted rudders are incomparable with wind vanes or below deck autopilots. ” We need to stop visualizing a Westsail 32 rudder and envision a design suitable for a boat like the A40-42. Vertical transom inside of a sugar scoop swim platform. Large diameter tube rudder shaft down to the water line held in place by two saddle style split bearings on the outside of the transom. Rapid removal with only four bolts. Pie shaped cut-out in the swim step, again removable with only four bolts. Full end plate effect. Only a couple of inches of offset for the Cape Horn windvane horizontal shaft. Rudder removable in minutes while in the water using main boom and halyard for lifting.

    • John Jul 26, 2014, 11:48 am

      Hi Richard,

      I absolutely agree. With a boat like the A40 we can come up with an innovative, elegant and inexpensive self-steering system without resorting to the kind of under deck power gobbler that many cruising boats have defaulted to. I expect that experimenting and perfecting self steering will be one of the larger parts of the prototyping process (fun and interesting too) and that we will end up with something very like what you suggest.

      Having said that, the point I’m trying to clearly explain here is that an electronic autopilot that steers at all times when offshore is a big and expensive beast that will cost the kind of numbers I’m talking about. As soon as one changes ones thinking to say that a vane gear will steer when the wind and waves are up, most all those costs go away.

  • Dick Stevenson Jul 26, 2014, 5:13 pm

    Dear John,
    You have made a number of comments about below decks autopilots being amp hogs and the how the subsequent cost of producing those amps must be added to the overall cost of the autopilot. I have no experience with the autopilots you are usually referring to and suspect they are the amp hogs you report. I do have 13+ years of living full time and wandering widely with a below decks autopilot. It is an Alpha 3000 which is known for being miserly with amps as well as its other attributes. It is hard to be accurate with how many amps are actually used: conditions vary dramatically and we are always running with much other equipment going on & off at intervals. That said, at no time have I experienced the Alpha as being a significant drain on the batteries. Having a big freezer more or less demands a genset, so we can’t say that the Alpha could be run on an ocean crossing with solar and/or wind generators, but I would not be at all surprised if it could (given a well balanced boat).
    The above in no way is meant to suggest a below decks autopilot for the A40. I think your reasoning is very solid in that regard and the anticipated alternatives more than adequate.
    Speaking of boat balance, what you say about below deck autopilots and boat balance bears repeating. Modern day autopilots are so powerful that a boat whose sails are out of balance may not exhibit the kind of symptoms that would lead a skipper to adjust things so his helm was eased. This will lead to a geometric increase in amps consumed and, it has been suggested, to rudder damage (especially if the rudder was not well designed, old or suffered a previous knock). A veteran observer of the ARC and other rallies once commented to me that he has observed a rise in rudder damage with an increase in autopilot use. He went on to say that inexperienced groups go out, sail their boat unbalanced with the autopilot sawing away. A week or 2 later there is rudder damage and the blame goes to a random whale they must have hit and they remain unaware of the abuse they have been delivering to their rudder.
    Every vessel with a wheel should have a Turks head indicating rudder amidships and practice keeping that knot in an area indicating just a bit of weather helm. Then, when underway, have it be part of the watches regular rotation of observations to check on where that knot is spending its time.
    My best, Dick Stevenson, s/v Alchemy

    • John Jul 26, 2014, 5:49 pm

      Hi Dick,

      All good points as always. When I say “amp hog” one does need to put that in the perspective of the boat: Amp hog on your Valiant 42 with big batteries, big alternator, and generator? Maybe not, although I think that if you actually accounted for all the amps consumed by your autopilot over 24 hours steering down wind in trade wind swells you might be surprised. I have conducted this experiment on a trans-Atlantic and the results were eye popping, and this on our boat that tracks as if she were on rails. (We turned everything else off for a full watch and tracked amps and if memory serves the power use of the autopilot alone was in the order of 100 amp hours/day.)

      Now even if you half that for the Adventure 40 to 50 amp hours a day you are going to exceed the available solar and probably wind power after taking into account other loads like electronics, nav lights etc. Yes, this problem is solvable in many ways, but to me the way that fits best with the A40 ethos of simple and elegant is just don’t have the large autopilot and use a vane gear.

      I 100% agree that autopilots promote poor sail trim. Woe betide the watch stander on Morgan’s Cloud if the king spoke is a long way from 12 o’clock when the skipper comes on deck!

    • John Jul 26, 2014, 5:55 pm

      Hi Dick,

      I just checked the specs on the Alpha 3000 autopilot. They say “input Current 15amps max. 2-3amps typical cruising on a well balanced, well sailed vessel.” That means 48 amp/hours a day at the very best. I would stick with my estimate that down wind in the trade winds the daily load would be close to 100 amp hours a day and certainly no less than 75.

  • patricksynge Jul 26, 2014, 7:41 pm

    I agree that reliable and powerful autopilots can be relatively expensive to purchase, install and use.
    But despite this I would no longer enjoy shorthanded, long distance, sailing without one – and the costs can be minimised.

    Having a reliable pilot to take over the steering in any situation is like having another crew member on board. There is no way any wind vane is going to be of much help when you are caught in a sudden squall with too much sail up and something jammed. And this is exactly the kind of thing that happens – usually in the middle of the night. Having ocean sailed extensively with 2 young children aboard my wife and I know how fatigue can sap you. And fatigue is one of the greatest dangers.

    I have previously mentioned the simple hydro generator I built from easily available components. It provides at least twice the current required for a powerful autopilot and only cost a few hundred dollars in components. Keep the sails trimmed and reduce canvas reasonably early and a correctly adjusted autopilot doesn’t use that much power anyway. Many people seem to forget that pilots have sensitivity settings and don’t adjust these to suit the conditions.

    Autopilots need not be that expensive either if you keep your eyes on ebay and the classifieds. Over the years I have purchased a “failsafe” collection of Coursemaster units comprising 3 course computers, 3 rudders sensors, 2 compasses and 2 drive units, 3 control heads. All in good second hand condition and easily interchangeable. Total cost $4000. Yes, I like autopilots!

    • John Jul 27, 2014, 10:52 am

      Hi Patrick,

      I agree that powerful underdeck autopilots have many advantages. After all, I have one.

      However, what we are talking about here is the Adventure 40 where we must stay simple to achieve the goals for the boat. Otherwise we are just going to end up with yet another $400,000 boat, or alternatively a poorly built boat because we will be robbing money from construction to fund convenience items.

      There are plenty of other ways to deal with a squall at sea or resting, including heaving-to, to name just one. The bottom line is that people cruised successfully short handed for decades before the advent of any kind of autopilot. Also, a good vane gear will be perfectly capable of steering an A40 in extreme conditions.

      There is even a pretty solid argument (see Dick’s comment) that clicking in a powerful underdeck autopilot “when you are caught in a sudden squall with too much sail up and something jammed” is not a good idea because it can exert huge force on the steering gear and maybe kick out or break something at the worst possible time.

      As to current use. The numbers I quoted in answer to Dick’s comment assume good trim and proper set up. There is simply no way to get away from the fact that steering with electricity at sea uses a lot of electricity. Yes, there are ways to make that electricity, but all of them add complication and expense.

  • RDE Aug 20, 2014, 9:40 am

    I thought everyone might enjoy this video of a lifting keel sailboat purposefully being run aground at 8 knots to test the keel design.

  • Archie Sep 10, 2014, 7:16 pm

    First time post. I’m not a sailor but very interested in the A40. It makes a lot of sense to me. Where would you not advise taking the A40? For example, assuming the owner has appropriate experience and is properly outfitted, would the high latitudes be too ambitious? A very different example, could you travel the canals of Europe? Second question, different subject, would you comment on Ted Brewer’s “comfort ratio”? The A40 doesn’t do as well as I expected. I think its primarily a function of its relative displacement but I could be mistaken. Great job to both Erik and you, not only on the A40 but your excellent web site!

    • John Sep 11, 2014, 8:27 am

      Hi Archie,

      High latitudes: see this post. As to the canals, I’m no expert, but I think she will be a bit deep at 6-feet.

      On the comfort ratio, keep in mind that it is a very simplistic measurement that does not take into account hull shape. Having said that, will the A40 have a more active motion with the wind forward than say a Whitby 42? Undoutably the answer is yes, for just he reason you state. Having said that the A40 will run rings around a Whitby on all points of sail. See the hull post for why this speed can make you a great deal more comfortable in the long run.

      Off the wind I would expect the A40 to be more comfortable than the Brewer boats because she will be going faster. Counter intuitive I know, but true.

      • Andy_G Oct 2, 2014, 5:27 pm

        I’ve been looking around at numbers for boats that I’ve been on trying to figure out which ones are the most important. Hull shape is very hard to quantify and makes a huge difference in that two boats with similar numbers will do two different things in each condition.

        I am however a little bit concerned with the D/L being half of the boats you often site when talking about the ones that “surprise with silver”. Are there examples of boats that sail really well offshore with (using the A40 “full load”) a D/L of 178? If there are I haven’t been on one so I appologize for the ignorance, if there aren’t I am optimistic that the amount of thought that has gone into this might produce the first one.

        I hope that this post isn’t read as rude, I really am just curious,

        • John Oct 3, 2014, 9:45 am

          Hi Andy,

          Good question. The thing to understand is that unlike the boats I was talking about, the Adventure 40 has the huge advantage of being designed with total disregard for any racing rating rules. This means that Erik was able to make her a lot longer for her weight.

          On the other hand a boat like say Selkie was designed to be competitive under the IOR rule which heavily penalized waterline length. The strange thing is that for decades these rating rules influenced hull design in negative ways even for cruising boats.

          It wasn’t until Bill (Fast is Fun) Lee and the Johnstones at J showed the way to good boats that ignored the rating rules that we got away from that.

          The point being that that heavy short boats are not desirable, they are the result of artificial influences.

        • Erik de Jong Oct 3, 2014, 10:05 am

          Hi Andy,

          In addition to John’s answer above, which is well said by the way, I have to add that a yacht is a complex set of balances which need to be right.
          Sailing yachts that are capable of planing set aside, weight does not matter at all, as long as the other parameters are in harmony with the weight of the boat.
          One needs to achieve the right ratio’s between wet-surface and sail area, sail area vs. weight, weight vs. length, the proper block coefficient, proper prismatic coefficient and so a few more parameters. These individual parameters and ratio’s don’t say much on their own, it is the harmony between all of them that determines if a boat is save, comfortable and fun to sail.

          Unfortunately, this is not an easy subject to explain since quite a bit is counter intuitive. I’ve been studying this topic intensively for 18 years now, from both a theoretical and a practical perspective and I’m still learning new things every day.

          • Andy_G Oct 4, 2014, 5:17 pm


            Thanks so much for your effort and time, I just helped a friend bring a Westsail 32 home which is obviously the other end of the spectrum from an A40. I have more miles than I can count on ships and medium sized working boats but am not anywhere near the miles under sail of the people who are working on this and I guess that I just don’t have any good comparison of a long skinny relatively light boat.

            I’ve been doing some inshore and near coastal sailing on my mid-generation Legend series Hunter (go ahead and laugh me out now) and looking for an eventual cruising boat once I can get free of the working life. I try to get out on anything that I can to see the differences and so I really like the topics on boat design and appreciate your time and effort.

            Thanks for all your hard work and patience,

          • John Oct 4, 2014, 5:37 pm

            Hi Andy,

            No worries, that’s what we try and do here.

            And no laughter about Hunters. Whatever one may think about the boats, there is no denying that they have got a lot of people out on the water, which, after all, is the idea.

  • Jaap vd Heide Oct 7, 2014, 12:30 pm

    Dear Erik and John,

    Could you also post a plan view of the lines?
    It would help me a lot to really see what Erik is doing.
    Using one half for waterlines (3-5 will do; 17 buttocks and 58 sections made it a bit difficult to “keep my eyes on the forest, not the trees” 😉 ).
    If you could put 3-5 diagonals and a curve showing the section area in the other half that would be great.
    Adding another plan view with dwl at 0, 10, 20 and 30 degrees of heel would be absolutely marvelous, especially when enriched with the position of LCF at the different angels of heel.

    Or would that be pushing it?

    And there is something else I have been pondering on for the last couple of weeks, so I might add well ask now:
    In his post from Greenland Erik designated both the reduction of inertia (heavy items – mass – in the extremities of the boat) and the reduction of buoyancy in the extremities as “weight”. While, as Laurent was hinting at, the first measure increases the natural response frequency in pitching and rolling and the latter decreases it. Could you tell what response frequencies you are aiming at? And along with that, for which circumstances are you optimising?



    • John Oct 7, 2014, 3:09 pm

      Hi Jaap,

      I think we will take a pass on publishing that level of line detail for several reasons. First off, this is a preliminary design. Erik still has a lot of computer modelling to do before he finalizes the lines, so getting into a detailed discussion now would not make a lot of sense.

      The second reason is that I think that getting into long and detailed justifications of each of his design decisions with all comers would be a poor use of Erik’s time. We simply can’t design by committee here. That way lies madness and a poor boat.

      That’s not to say that Erik in any way thinks he has all the answers—although I can tell you that he has a lot of them. His final design will be reviewed by another professional naval architect, a lot better solution to coming up with the best design—too many cooks would spoil the broth.

      And finally, keep in mind no one needs to take our word for it that this boat sails well, since there will be a prototype available to test, prior to buying.

      I will leave the rolling question to Erik.

      • Jaap vd Heide Oct 7, 2014, 3:34 pm

        Hi John,

        I wasn’t asking any lines detail you haven’t already published. Just another view. You already published 2 views, which means I can construct the third one. It’s just that it probably is a lot less work for Erik and his CAD workstation. It should be possible with less than ten mouse clicks and twenty key strokes.

        But if you rather not publish more lines, no hard feelings here. My love lies with cruising on the Dutch inland and coastal waters so I won’t be in the market for an Adventure 40 anyway. I am just curious and those diagonals would be very nice to have to compare them with other boats. So I’ll just construct them myself. 🙂



  • Tom Minerick Oct 11, 2014, 12:32 am

    Any thoughts on the steersman for self steering?

  • Bob Dec 12, 2014, 9:23 am

    My 15 year old daughter, for her 10 grade Gymnasium physics class, has taken on the onerous task of calculating the relative speeds between the brigantine she sailed on this summer and our modern sloop rigged boat (a 2003 Bavaria 49).
    I have a copy of Skeen’s EoYD she is reading but I was wondering if there is a more modern “Beginners guide to understanding Yacht Physics”??
    It is great that she has this drive to do this but it is NOT and assignment, if she only worked this hard on her homework…..(now I sound like a parent!)


    • John Dec 12, 2014, 10:06 am

      Hi Bob,

      The modern equivalent to Skeens is Principles of Yacht Design although you may not thank me for this recommendation because if your daughter really gets into said book, here homework will never get done!

      • Jaap vd Heide Dec 12, 2014, 10:27 am

        In the curriculum for Maritime Engineering at Delft Technical University (home of the Delft Systematic Yacht Hull Series – which are now in the public domain), Larsson’s PoYD has already been deprecated in favour of Fossati, F., “Aero-Hydrodynamics and the Performance of Sailing Yachts – the science behind sailing yachts and their design”, International Marine/McGraw Hill, 2009, ISBN 978 0 07 162910 2.

        My bookshelf holds both, when they’re not on my desk. 🙂
        The students at Delft use the book in a two-fold course: first design a sailboat, then build it – to scale – and race it RC-controlled in one of MARIN’s test basins. Why is it that at times I wish I was a student once more?

        • Erik de Jong Dec 12, 2014, 11:11 am

          Hi Jaap,
          I do agree with you that within the yacht design community the book by Fabio Fossati has indeed more or less replaced “PoYD”. But it is so much more scientific that anyone without a half decent physics education and basic knowledge of Naval Architecture in general will have a very hard time understanding what it is all about.

          For understanding more about the basic principles, like the relative speeds of a hull that was used as example in the question, PoYD is a much easier read and will get you what you need.

          I’m almost inclinded to say that PoYD is book 1 to read, and Fabio’s book is the follow up to get more indepth.

          • Jaap vd Heide Dec 12, 2014, 12:44 pm

            Hi Erik,
            I fully agree. That’s why *both* still find their way to my desk on a regular basis. 🙂
            As an introduction for Bob’s daughter Eric Sponberg’s “THE DESIGN RATIOS – A Naval Architect’s Dozen (or thereabouts)” might be a great start too.

  • Bob Dec 12, 2014, 11:06 am

    Thanks John and Jaap vd Heide
    John, it is if you know my daughter….
    Jaap, I have applied for access to the Delft’s site.
    “Oh what have we wraught!”

    • Bob Dec 12, 2014, 11:20 am

      Both books ordered.

      • Bob Dec 12, 2014, 11:41 am

        And John, my wife just said ” If Erika’s grades take a nose dive you can go live with John!” Just so you know, I make a mean Cappuccino.

        • Bob Dec 13, 2014, 10:58 am

          Jaap, Erika is reading the Sponberg PDF (I read it last night). If she reads through and wants more info then it is the other 2 books.
          Thanks all for the great response. No wonder I like hangin out with BP’s!

  • Claire Jan 6, 2015, 11:38 pm

    I just encountered a very interesting site on the design and build of a boat with design objectives very similar to those of the A40. It’s Nordkyn, at

    There are a few differences of detail (e.g. no kick-up rudder or hard dodger, acceptance of a deeper draught) and Nordkyn is a one-off aluminium boat rather than a series-built GRP hull, but essentially it’s the same spec: a boat of about the same weight and same length, designed to be robust and simple and above all to sail fast and comfortably on ocean passages, including light airs and upwind sailing in heavy conditions without pounding.

    It’s interesting that Nordkyn ended up with a hull shape close to the contemporary mainstream than the fine-ended A40. Nordkyn is about 1 foot beamier, has a much broader stern, and a lot more buoyancy forward.

    The owner-designer-builder says that Nordkyn meets all her goals, including safety downwind in big seas (something to which he has paid a lot of attention).

    One spin-off is that Nordkyn’s wider stern allows a much more versatile accommodation layout. I don’t know to what extent that was a design goal; it’s not explicitly listed, but seems to me to be implicit in some of the explanations.

    I haven’t found any external commentary or assessment of Nordkyn, so there is only the owner-designer-builders extensive commentary. But from what I can see, Nordkyn looks like a very important comparator for the A40. If Nordkyn performs as well as claimed, there are grounds to consider Nordkyn as a better solution than Erik’s design.

    • Marc Dacey Jan 7, 2015, 1:39 pm

      A very interesting read, not only for the actual boat created, but in terms of the philosophies driving the ultimate design, which of course is a big part of the Adventure 40 project and which are largely ignored or “half-assed” in the current world of production boats.

      While I am “dancing with who I brought” in terms of refitting (in the fuller sense) an existing boat for long passages/living aboard, I do find these sort of projects interesting as they give me ideas about how to handle systems and stowage on our own vessel. Thanks for posting it. I can’t help but think it is more complementary rather than antagonistic to the goals of the laudable Adventure 40 project.

    • Laurent Jan 7, 2015, 3:40 pm

      I am a bit frustrated not finding more cost figures on Nordkyn site. I think it is a bit unfair because for the Nordkyn as well as for the A40, economic considerations are described as significant parts of the reasons of undertaking such projects instead of buying stock products.
      The only figures I found (on page indicate that “Engine, transmission, shaft, propeller and all associated material costs” make 9% of “direct material costs”, which make about 48% of total costs.
      We see some pictures of the engine in page: project>construction>engineering. It looks like a good quality new marine engine in the 60 to 100hp range. Estimating the cost of this engine + transmission +… to 25k $, that puts the whole budget (including work time…) to 25k$ * 1/4,32% which makes 578,703$, that is about 3 times the A40’s target cost.
      For this price they have a bigger boat and this bigger boat is also proportionally wider, because A40 low width/length ratio was mainly due to water-length/critical speed considerations, that apply much less to the Nordkyn, because it is already more than42′ long with a classic width/length ratio.
      Personally I feel a bit frustrated by the monacal (clinical ?….) interior for a #600k$ boat, and the 2,35m draft seems a bit too penalizing in my opinion.

      I understand that Nordkyn builder probably got a very good performance level with this boat, but I guess he could have built a longer, narrower and simpler boat with: same or better performances, lower draft and lower cost, or better accommodations for same cost. This boat wouldn’t be the A40 either, but it could be part of the debate about optimized long-range cruising boats in the 600k$ range….

      • Claire Jan 7, 2015, 6:21 pm

        Laurent, I think you may be mistaking the costs of that build style with the costs of building that particular design. A one-off alloy build with painted hull and deck is inevitably a lot more expensive than the series-produced GRP in which the A40 was costed.

        You wrote: “I understand that Nordkyn builder probably got a very good performance level with this boat, but I guess he could have built a longer, narrower and simpler boat with: same or better performances, lower draft and lower cost, or better accommodations for same cost”

        My point was that the Nordkyn and the A40 have approximately the same displacement, which John reminds us regularly is the main determinant (assuming that the style of construction and finish are similar).

        Personally, I prefer the easily-cleaned painted interior to a varnished wood cave, but tastes vary. However, AFAICS the choice of fitout is not the significant difference between the fine-ended A40 and the more sled-like Nordkyn.

        • Laurent Jan 7, 2015, 7:02 pm

          re cost of the Nordkyn:
          I looked at cost infos on the whole Nordkyn site and I didn’t find much of it, which is a bit worrying, because that guy is basically trying to sell the idea that he got a better value/cost ratio than current offering for blue-water boats, and he doesn’t really give figures that could help to demonstrate that. The only figures I could find on his site (page : refer to “The Cost of Yacht Building” in general terms. So, considering that he is more or less selling the idea of series-building copies of his boat, it seems logical to consider that those costs refer to this kind of series-building for his boat and not to his one-shot DIY building. If not, he would not have quoted workmanship as 42% of total. There is no “workmanship cost” in DIY building.

          re: cost vs. displacement
          same displacement boats using same technologies and same level of finishing should have similar building costs (assuming similar efficiency of builders, similar wages for employees etc…). Here we have very mature technologies (glass/vinylester composite hul, molten iron keel etc….) vs. much more expensive ones (aluminium hull, aluminium + lead keel etc…). In that case displacement is not relevant as a cost estimate. Same logic in car manufacturing. You can compare costs of BMW series 5 with equivalent Mercedes on a weight basis, you can not compare the cost of carbon-fiber BMW i3 with that of a Dacia Logan on that basis.

          re: fitout
          Reading the infos on Nordkyn site, I understand that estimate for series-production costs of the Nordkyn is #600k$ with a very (excessively?…) basic interior. I don’t think there is much market for that at 600k$, but anyway the A40 project is addressing the question of blue-water sailboats in the 200k$ range, which is a very different question.

          • Claire Jan 7, 2015, 8:21 pm

            Laurent, are we reading the same website? Your post above seems to me to be based on a set of completely false premises.

            I see nothing at about series building. The whole page is devoted exclusively to issues facing self-builders or people who commission one-offs.

            You write that ” he is more or less selling the idea of series-building copies of his boat”. I see nothing at all to support that assertion.

            It’s not just that the site doesn’t mention that explicitly. There are no lines, no deck layout plans, no accommodation plans, no hull profile; there isn’t even any info on whether it is possible to even see a copy of the plans.

            You write you “understand that estimate for series-production costs of the Nordkyn is #600k$”. I can find no such figure on the Nordkyn website; the 600K is YOUR figure based on an extrapolation of your assumption that Nordkyn has 60 to 100hp engine — 2 to 3 times the size specified for the A40. It’s basically a guess.

            This all seems intend to set up your apples-and-oranges comparison. It would be quite possible to build the A40 as a one-off aluminium boat with faired and painted hull and decks, and 3 watertight bulkheads. But as John Harries has repeatedly pointed outs, the costs would be way higher than the mass-produced GRP boat he intends.

            My reason for posting the was in comparing the design principles, not in a contrived comparison of the costs of a professionally handbuilt one-off with a no-options, no-frills series boat.

            That fact remains that the two boats have similar length and similar designed displacement. Built in the same materials the slightly more voluminous Nordkyn would be a little more expensive; but it would not be 3 times the price.

          • Laurent Jan 7, 2015, 9:50 pm

            Claire, do you know anything about business?. I read on the Nordkyn design site : “© 2013 Eric Bretscher, Nordkyn Design” and: “Nordkyn Design is run as a marine design office and consultancy, and started with the objective of transposing years at sea and a scientific and engineering background into a design advantage. It is about vessels with phenomenal sea-keeping characteristics, born from first-hand experience over tens of thousands of miles at sea in all weather and all parts of the world.”, which means in a language you can read, that M. Bretscher has developped this site in order to find customers for his design office & consultancy practice, and, obviously enough, he is selling design & consultancy work related to the sailboat he designed and built.

            I just can’t understand why the absence of Nordkyn 43 ….”lines, deck layout plans, accommodation plans, hull profile”… on his site should worry anybody in that profession. Just imagine that M. Bretscher market notoriety is not (yet) very high in that business, and he quite logically chose to publish only minimal informations about his boat for (possibly legitimate…) fear of copyright violation.

            He is quite clearly selling “marine design [services] and consultancy”, including design services related to the Nordkyn 43. In plain English this means that he is selling (among other things…) copies or adaptations of the Nordkyn 43 plans for professional or amateur building, one-off or series.

            I quite understand he might not want to publish hull profiles etc… on his site. I am a bit frustrated he doesn’t give more cost informations on the Nordkyn 43, considering he argues that this boat has a very good or better than existing equivalent product value/cost ratio. Reading his site, I went to the (obvious) conclusion that his page contain all the information he is willing to publish about the cost of the Nordkyn 43, and that it does concern this boat. Obviously he didn’t choose the worst case scenario (one-off…) to make his estimates (he was not supposed to anyway…).
            I understand that literate readers of his site have enough technical and cost informations to understand what he is speaking about, and to contact him for further details if they have serious business interest for this boat.

            Considering the engine, you can see it on the 7th picture of this page, and it is obviously more, or much more, than 20 hp.

            Considering series vs. one-off, there is no law preventing boat-builders from making series aluminium sailboats, so saying that John excluded aluminium for the A40 because it is reserved to ones-off is silly. Series aluminium A40, or A40 equivalent, could easily be built cheaper than aluminium one-off, but the cost of aluminium series boat is generally higher than glass-vinylester composite series boats, so John concluded that aluminium is probably not the best material for his project.

            Personally I was discussing Eric Bretscher Nordkyn 43 vs. John Harries A40. I see now that you were in fact discussing a very special version of Eric Bretscher Nordkyn 43 using John Harries A40 materials. That is exactly what I call a “committee boat”, I am not very much interested in discussing that for obvious reasons.

            I have a US friend, who is a computer engineer like me, and who is very critical about US MBAs. He considers that this diploma only shows that corresponding guys can read, because you only need to now to read to pass this exam. Next time I see him, I guess I might tell him that it might be useful to know who has proven he can read before trying to explain something.

    • Erik de Jong Jan 8, 2015, 10:22 am

      Hi Claire,

      Thank you for sharing this link. I was not aware of this very interesting project, and it looks like we have very similar design requirements as well as solutions.
      It is difficult to compare boats from pictures that are taken at random angles, but what I see is that both the designer of the Nordkyn and myself came to the same conclusions regarding the hull shape in relation to seakeeping and performance trade-offs. There are only very minor differences between the Nordkys hull and the Adventure 40 hull, and none of these differences really influence the seakeeping conditions that much.

      What I see from the pictures, is that the A40 has a slightly deeper fore foot. The reason I opted for this, is that the boat is less prone to slam on the waves. There is nothing wrong with slamming from a performance or sea keeping point of view, it is just annoying to the crew and can be avoided.
      The other difference is that it looks like (not sure if it is!) that the transom of the A40 is slightly narrower compared to overall width. I opted for a relatively narrow transom to get the least amount of trimming when heeled over. That makes the boat steer lighter when heeled, and increases upwind performance.

      The most obvious difference is the overall width of the hull. A narrower hull drives easier, is less prone to rolling in swell with no wind and gets away with less engine power and lower fuel consumption. The downside of a narrower hull is that the boat’s capability to carry sail is reduced, and that there is less space for the interior. Hull width has only a minor influence on the seakeeping characteristics of a boat, and the difference between the Nordkys and the A40 is almost negligible from that perspective. So in the end, the designer (or actually the owner) needs to make the decision between easy driving or more interior space.

      We have opted for the easier driving for the A40, as that reduces strain on the people onboard since you sail with less sail area. It also reduces the weight and the cost of the engine (30hp in the A40 vs 40 hp in the Nordlys), as well as reduced fuel consumption and therefore a reduced required tank capacity.
      The trade off is that the interior volume is reduced. In the case of the A40 not really a big deal as the boat is designed around a cruising couple, all interior one needs and can get for the price tag will fit the A40 hull.

      So is the Nordkys a better solution? depends on what you are looking for. Both the A40 and the Nordkys will have very similar performance, very similar sea keeping capabilities, and get you where you want. The difference is that the A40 has less interior, but travels at good performance at a lower power. If the gained interior space is what you are looking for, and you have the budget to pay the extra money for it, than the Nordkys is probably the better boat for you. If you like to get somewhere in comfort and at speed and are on a tight budget, the A40 would be the better choice.

  • Claire Jan 7, 2015, 11:49 pm

    Laurent, Eric Bretscher does indeed appears to be selling his design services. Our disagreement is that I don’t see any evidence of the leap you make beyond that to the proposition that he is marketing the Nordkyn design, or the next step that he is pitching it as a project for series production, let alone that he has a price point in mind for series production. If he is indeed selling “copies or adaptations of the Nordkyn 43 plans for professional or amateur building, one-off or series” (as you claim), it’s odd that there is nowhere on the site that he actually says so.

    Those are all your assumptions, and projections. Fine, feel free to speculate; speculation is interesting. But it would be nice of you to refrain from accusing people of failing to read something which isn’t there and to make barbed comments about literacy.

    If you go back to my original post on January 6, you’ll see my interest was in the significantly different hull shapes which two designers had produced in response to similar design briefs.

    Those hull designs could be produced in a wide variety of materials, on a custom or series basis. Since this is a discussion on a page about A40, I was interested in considering a) how Bretscher’s design compared with Erik de Jong’s response to a similar brief, and b) whether Bretscher’s design was a viable alternative for the A40 project.

    That’s not a “committee boat”. It’s an exercise of taking all the crucial elements of the A40 framework, and plugging in a different hull shape. If you don’t want to discuss that, fine.

    You want to compare the well-documented proposals for a series-built A40 with your speculation about the costs of a series-built Nordkyn using very different construction methods. I find that comparison a bit outlandish, so I won’t continue that discussion.

    We’re talking past each other, so best to leave it 🙂

    • Laurent Jan 8, 2015, 9:23 am

      1)- Eric Bretscher is clearly and obviously talking business on his site (contrarily to what you affirmed earlier…) and you need to be able to read business in order to discuss about his offerings and/or the technics he presents on his site as part of his business offering. If you don’t understand the (limited…) pricing informations he gave about the Nordkyn 43, I have every reasons to conclude that you are not able to read business informations.

      2)- On a purely technical ground, Eric Bretscher presents his work as an innovation in hull design, using advanced computer technics (he has a MS. in computer sciences…) where he was able to develop a new kind of hullform with most of the advantages of modern planing hulls without the corresponding drawbacks, plus some special advantages related to heavy weather handling. He published only very limited informations about those hullforms, for obvious industrial rights/copyright reasons, and we are not in a position to discuss their possible adoption because we know only the purpose and the (reputed…) results but not really the recipes.

      Being a computer scientist and quite literate about boat architecture, I could try to guess what his recipes are. I won’t do that, because I consider it as futile if too far from truth, and as dishonest to Eric Bretscher if too close. I think this is quite simple to understand, and that Eric Bretscher informations on his site about: his purposes, the Nordkyn 43 technics and the cost of this boat are as clear as appropriate in that case.

      This said, we can discuss about the Nordkyn 43 vs. the A40, or about Claire special improved version of the A40, but I don’t think it might make sense to discuss about some kind of mix and match of the Nordkyn 43 and the A40 with all the advantages and none of the inconvenient of both, while we don’t really know, in fact, what the Nordkyn 43 innovations are…..

      • Jaap vd Heide Jan 8, 2015, 9:45 am

        Dear all,
        mr. Bretcher has quite recently (February last year) also found a position of “doctoral candidate” (researcher/phd student) at the University of Auckland. None of the search engines aimed at scientific publications come up with anything yet, so I guess we will have to wait for that for some while. His LinkedIn page already states he is working on “Hull form research and development using RANS CFD solvers, parametric modellers and optimisation algorithms” though. He has got me interested, I’ll just wait and see. 🙂

        • Jaap vd Heide Jan 8, 2015, 9:56 am

          Digging a little deeper reveals he will be presenting a paper entitled “Towards the development of a class of fast, stable and seaworthy displacement monohulls using parametric optimisation and CFD” at the High Performance Yacht Design Conference that will be hosted by the University of Auckland early March, during the Volvo Ocean Race stopover, where he will be joined by people like Lars Larsson. []
          We might not have to wait very long.

        • Jaap vd Heide Jan 8, 2015, 10:05 am

          The abstracts are also on the site: his scientific work is aimed at motor yacht hull design in the Fn range 0.5 – 1.0 .
          Not a very feasable operating window for a shorthanded cruising sailing yacht.

  • Bill Attwood Jan 8, 2015, 5:31 am

    Hi Claire and Laurent,
    An interesting debate, which confirms the value you both add to this website. Just a pity that this time it got a little too personal.
    One thing which struck me from the Nordkyn website was the sort of sailing for which the boat is designed, and the designer’s heavy weather ideas. They seem to significantly different to those of other experienced voyaging sailors eg his comments about the JSD. He personally also sounds to me to be in the mould of Tabarly, not an ordinary mortal like the most of us. Could it be that the A40 design would be better able to look after a crew of normal mortals than the Nordkyn? Finally, I find the A40 much prettier.
    Yours aye,

  • Henry May 24, 2015, 9:42 pm


    The longitudinal profile and perspective drawings look very nice and give the impression of a well balanced hull.

    The midships section shows you’ve gone for an almost circular form. I understand this yields low wetted surface area/displacement but I am wondering if it will make the boat a little tender?

    Can you say what wind speed close hauled will heel her 10 deg. unreefed?


    • John May 28, 2015, 8:31 am

      Hi Henry,

      Erik is in Greenland and will be offline all summer.

      Let me have a go: You are, of course, right that the boat will be initially more tender than a wider boat or one with a harder turn to the bilge.

      But on the other hand because the boat will be so easily driven you will be able to get away with a lot less sail area for a given wind speed. Also, the ballast is concentrated in the lower third of the keel, which will stiffen her up quickly as soon as she heels a bit.

      Our boat is a bit the same way (relatively narrow with a canoe type body) and she goes to about 18-22 degrees (low compared to many boats) of heal when beating, and then stays there.

      Also, the A40 is based on the hull form of Erik’s own boat that has proven extremely comfortable when going to windward at sea, to the point that the main paying crew accommodation is well forward of the mast!

      In summary, comfort at sea is complex but having an easily driven hull so less sail can be used to maintain power to push through the waves seems to trump all.

      So, given that, the amount of wind to heal to 10 degrees is not really a very useful number since no monohull sails with the wind forward of the beam at a heal angle that low. What really matters is what heal angle you can actually make progress at and how soft the motion is, and here the A40 will eat the lunch of wider boats with a harder turn to the bilge, just as boats like Carina do.

  • Henry May 28, 2015, 10:17 pm

    Hi John,

    I understand it’s a silly way of framing the question but I was endeavouring to get an idea of the stability of the boat given it’s rig and ballast. Although I’m not sure that I would agree all monohulls behave with heal in the way you describe. Going the other way of hardening up the bilge or increasing beam starts the design spiral in the other direction (more displacement or less headroom if underbody depth is pulled up to compensate) along with some undesirable dynamic stability issues. I was reminded of Steve D’s Sundeer 67 whose midship section was pretty much circular – the boat was tender even though it was a ketch (Steve endeavoured to rectify this problem in the later Sundeers I understand). That’s what prompted the question. After your post, I rechecked the 67’s midship’s section and it is fairly extreme. In comparison, the A40’s looks like a nice compromise.

    • John May 29, 2015, 9:01 am

      Hi Henry,

      Yes, I think you are right, it’s all about the compromise, but I really do think Erik has that right. Keep in mind that the A40 is a has a much deeper draft in relation to it’s size than the Sundeer, that coupled with the lead ballast being concentrated in the bottom of the keel, will make her heal resistance go up very quickly as the angle increases, something that narrow boats need to sail well.

      The decision to go to 6′ of draft was one of the most difficult Erik and I were faced with, but going that way has lead to all kinds of benefits that let Erik refine the boat in other ways. Short answer, she will be a giant killer upwind.

  • Rob Hellier Dec 3, 2015, 9:10 pm

    Hi John,
    Although my partner and I will be investing in an ocean capable craft, we will also continue to sail the Great Lakes as we’re based in Ontario. As you know, draft is a growing issue for Great Lakes sailors. Our current boat is just under 5′ draft and we have promised ourselves not to invest in a boat whose draft is greater than this. The A40 is currently designed with a 6′ draft which will pose problems in many great Lakes club/marina slips. I’m just wondering what are the trade offs of adapting a keel giving a draft closer to 5′? I would guess that a number of potential A40 buyers are also Great Lakes based with ocean sailing experience/aspirations and would be keen to see lower draft in the A40 design.

    I’m also wondering about Twin/bilge keel designs. in your blogs you’ve written a number of times about not wanting to adapt swing or lifting keels because of their complexity and cost. Bilge keels however, are simple, achieve similar stability at lower draft and offer the ability to dry out in tidal areas which I’ve heard is an important economizing feature in not needing a travel lift to scrape/repaint the hull or conduct repairs. I’m guessing that you and Erik considered this possibility at some point. Could you discuss your rationalle with regards to fin keel vs bilge keels?

    Thanks so much and I look forward to hearing more news on the A40.


    • John Dec 4, 2015, 8:44 am

      Hi Rob,

      Draft and keel design was one of the design areas that Erik and I agonized over the most. In the end, we decided that six feet was the best compromise between performance and draft, but, as you point out, it won’t be ideal for everyone. I expand on that more in the post above.

      And no, we did not consider bilge keels. As I say in the post above, a really useful shallow draft boat needs to draw less than 4 feet and a bilge keel boat drawing that would have really terrible performance up wind. There is also a big wetted surface hit with bilge keels.

      My thinking is that if one really wants a shallow draft boat, then a lifting keel boat is a way better option than bilge keels.

  • Rob Hellier Dec 4, 2015, 7:20 pm

    Hi John,
    Thanks for your thoughts on bilge keels. Some of the newer bilge keel boats by, for example, RM Yachts in France have likely found quite good all round performance with their aluminum hulls and high aspect ratio bulbed keels, don’t you think? Boy they sure look good drying out at low tide! The RM890 is closest in size to the A40 but i guess one will have to fork out at least another $200,000 for that baby, compared to the A40’s projected price.
    More realistically I’ve been looking at aluminum hull kit designs. Some of the most intriguing, at least to me, are by the Australian based Brazilian designer, Roberto Barros (B&G Yacht Design). They have a few swing keel, twin rudder, multi-chine aluminum hulled (34′, 36′ and 41′) sailboats that are designed for unrestricted ocean sailing. Their kits can include the CNC files to get the aluminum cut to high precision, which saves a lot of time for the fabricator. I’m thinking of buying a kit, obtain quotes from a couple Brazilian builders who previously constructed these yachts, get it built and rigged there, then do the interior myself . All this includes travel and management of contractors, selecting components, etc.. Avoiding this is one of the A40’s most attractive selling points. It’ll be interesting to see how the cumulative prices of a kit build will compare to the A40.

    In the end it’ll likely come down to either purchasing the completed A40 and putting aside my wish to have a boat that can tuck up to shore/dry out or investing time and money in a steel or aluminum hulled lifting keel kit. So that’s why I’m following your design process with such interest.

    • John Dec 5, 2015, 8:40 am

      Hi Rob,

      Good analysis of the tradeoffs. I think that for most of us, actually getting out there sailing is better than getting everything we wish for, and that’s the fundamental goal of the A40.

      One other point on going custom and that’s the financial risk, which is huge. Resale value of custom metal boats tends to be abysmal, and then there are always the risks of the build going wrong, cost overruns, or the yard going bankrupt. Custom builds are not for the faint of heart!

    • Jo Dec 5, 2015, 12:22 pm

      Hello Rob,

      Fora Marine is specialised in plywood yachts with epoxy, not aluminium. Thus the RM890 is wood with epoxy. It costs around $110000 and is smaller than the Adventure 40. The equivalent would probably be the RM1270 which is over €2500000, thus more expensive.

      But I agree with you, they’re beautiful boats.

      Here’s a link to a review of the RM890:

  • Rob Hellier Dec 5, 2015, 9:31 pm

    Hi Jo,
    Thanks for the correction. When I looked at the mutli-chine hull I assumed it was aluminum. I’ll do more research next time before singling out a particular boat

    Thanks too, John. I’ll ponder the risks of custom build quality and their resale value. To be perfectly fair to my options, however, there’s also the risk that the A40 may not go anywhere and us potential owners may wait 2-3 years before finding out that we’ve waited in vain. I know you’ll be doing everything in your power to prevent that from happening but your small team still has many many hurdles to cross as well.

    I am looking forward to more news on the A40. Whatever happens, it’s been a very valuable discussion that has many of us pondering what a blue water yacht really needs.

    Cheers, Rob

  • Iain Dec 27, 2016, 8:13 pm

    Loving reading about the Adventure 40, and its evolution. just a quick point, why is the rudder not protected with a skeg? I would much prefer the rudder to have a full length (even 3/4 length ) skeg to protect it…

    • John Dec 28, 2016, 5:04 pm

      Hi Iain,

      Like most everything in boat design, there are tradeoffs here. The key one is that if we hang the rudder on a skeg it can’t be balanced, even partially, and that will make the boat harder to steer with a tiller.

      Also, I believe that Erik is planning for a cassette type design which will make it easy to replace the blade if it is damaged. Again this would not be possible with a skeg.

  • Paul Mar 13, 2017, 6:58 pm

    Hi John,

    I really don’t want to capsize at sea – ever. Yes a keeler will roll back up afterwards but even so “No Thanks.” I’m starting to see the real sea-sense of James Wharram’s catamarans. But returning to a monohul, which seems to provide better cold-weather accommodations for an equivalent cost boat, the biggest risk for a monohul seems to be descending a large wave when the ballast becomes ineffective for the duration of the fall. The solution is to bear away on cresting the wave to go over lengthwise, rather than beam on. In this situation, is there a risk that a transom-hung rudder will not find enough solid water to bite into and bring the yacht around as it goes over the top?

    Or should one have hove-to well before things got this bad? Am I right to assume that yachts don’t capsize when hove-to?


    • John Mar 14, 2017, 8:56 am

      Hi Paul,

      I come at this discussion differently: Once control is compromised at all, any boat, particularly one with a short handed crew, should have long been in survival mode either heaved-to or towing a drogue. The bottom line is that any boat, no matter how stable (dynamic and/or static) will be flipped by a big breaking wave that broaches her. We see this over and over again in yacht disasters at sea that almost always start with a capsize that occurs because the boat continues to run off longer than they should have.

      Bottom line, handling and seamanship trumps boat design every time, as you say in your last line.

      And no, boats do not generally capsize if hove-to properly. The key is the boat must stay behind her own slick to be safe, see this chapter:

      As to control with an transom hung rudder, all the factors at play are beyond my yacht design pay grade, but I can say that many transom hung rudder boats do very well in this regard. Ocean 60s come to mind.

  • Maxime Gérardin Apr 14, 2020, 11:39 am

    much interesting, as always!
    I wonder why the largest beam is so aft (and probably behind the center of flotation). What would be the pros and cons of bringing it closer to the bow, as it is for instance on most J-boats? To me, it feels like this would bring more stability at high speeds (memories of fast downwind runs on J80 come to mind!), at the price maybe of a bit of speed, as the boat tries to “climb over” the bow wave. But maybe this comes from observations on relatively flat waters, and won’t hold in bigger seas?

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