Hull Design Torture Test

©2018 Steve Dashew, setsail.com

Steve Dashew, over at setsail.com, just published a post about being offshore in a short-lived but very nasty blow earlier this summer.

The super interesting thing is that Steve and Linda had just fitted their 78-foot motorboat Cochise with continuously running video cameras. The result is a uniquely useful set of photo-observations, coupled with written analysis, from a guy with a uniquely deep understanding of hull forms.

Doesn’t matter what kind of boat you sail or motor (or aspire to), I highly recommend you read Steve’s post. There is just too much good information about how hull forms work, and don’t work, in big and dangerous waves to let this one pass you by.

Here are two of my takeaways:

Buoyancy needs to be balanced fore and aft

“Cochise” from the bow and stern.

I have long ranted against overly-wide sterns for a whole bunch of reasons. But in Steve’s article we see graphically how vital it is that the stern does not have too much buoyancy, particularly in relationship to the bow.

For if the stern is too wide and big, as we see so often these days, then in heavy weather bad stuff will happen:

  • When running downwind in big seas, the stern will rise excessively on the back side of a wave and so stuff the bow, potentially causing the bow to lock in, resulting in loss of steering control, untimely leading to a broach.
  • When pushing into waves, the stern must be able to immerse well into the back of the last wave so that it does not drive the bow hard down into the front of the next wave by lifting too much, and in so doing bring tons of potentially boat wrecking green water aboard.

On displacement hulls—planing hulls like Open 60s are different—these two requirements are fundamental and immutable for safe offshore voyaging, as I can attest from having spent literally thousands of hours over the last 25 years watching how Jim McCurdy’s perfectly balanced bow and stern buoyancy react to waves.

Reserve Buoyancy Matters

Another interesting thing from the photos is the way that the flare in her bow sections, together with the resistance of the large anchor and associated platform, helps to stop Cochise from burying her bow excessively.

On Morgan’s Cloud, McCurdy achieved the same thing by carefully flaring the bow and adding moderate overhangs that gently, but firmly, prevent the bow from completely burying in the face of a sea, but still don’t provide excessive buoyancy that would cause slamming and/or excessive pitching.

This same reserve buoyancy prevents Morgan’s Cloud‘s comparatively deep forefoot from locking in when running hard off the wind.

Bottomline

It’s hard to imagine two boats more different than Cochise and Morgan’s Cloud, and yet the fundamentals of good hull design, which makes them safe offshore, are the same, and include balancing the bow and stern so that they work together, instead of drawing a design to accommodate a palatial interior. We ignore these fundamentals at our peril.

Artnautica LRC 58

Before I leave the subject, reading Steve’s post and studying the photos have got me thinking about the LRC 58 again. I always said that the court was out on what her heavy weather performance would be like, and Matt Marsh, AAC Engineering Correspondent, wrote:

When outrunning a following sea, she should be fine, but I suspect that when waves are overtaking her from astern, the seas will tend to lift the stern and stuff the bow. It looks like she has enough reserve buoyancy up front to handle this, but it’d make for a wet ride, and she’ll need a big rudder and strong autopilot to avoid any tendency to broach or bow steer if there’s a real nasty storm coming up from astern.

I also note that in his latest design being built in Turkey, it seems (from a cursory look at these photos) that Dennis has made major changes to the hull form,  including making the stern narrower and less buoyant than the LRC 58.

Steve’s article reinforces my thinking that anyone taking an LRC 58 into harm’s way fit her with a series drogue to Don Jordon’s design and, in addition, dispense with the large cockpit (as discussed in this post) since I’m not at all sure that keeping going in bad weather, either upwind or down, would be a good idea.

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Meet the Author

John

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.

35 comments… add one
  • Stein Varjord Sep 6, 2018, 12:27 pm

    Hi John.
    Good points, as always. You mention that these issues are different on planing hulls, like the Open 60 class. I think it might be interesting to look a bit more at that point, since it seems to be linked to how monohull cruisers are developing these days.

    The reason that extreme racers behave differently is complex of course, but I think two elements are interesting:
    – Very large hull volume compared to total weight and a speed that gives dynamic lift. Meaning they float/plane “on top of” the water, and they don’t easily get pushed properly under. They do, of course, get a lot of water on deck, but that is mostly water sliced off the sea surface rather than the bow digging into the sea.
    – They are sailed by elite sailors who are on non stop maximum attention level, and they accept a very high risk of serious trouble.

    No present day cruising boat is able to operate sufficiently on top of the surface, no matter how they’re designed. No cruiser, with a decent mental health, wants the work, stress and risks of pushing as hard as the racers. The obvious conclusion is that using core elements of the hull shape of an ultralight racer for a cruiser will have some problems. Why then do the boat wharfs do it?

    The first and obvious reason is that a fat transom gives a lot more space inside, which makes the boat easier to sell and nice in a marina. This item is the logical one. Then there is the other reason, which I think might be just as important:

    Racers innovate non stop. A top level racer from today looks radically different from and is dramatically faster than the same from a couple of decades back. We see every visual element of the newest racers as identifiers of speed and power. What that is has changed just as much as fashion in clothes. The extremely long overhangs, bow and stern, of the R-Class (12 meters etc) were defining cruisers, even though the overhangs are very bad for speed but were there to fit the R rule. Moving forward, we got the straight bows. Wow, that looked mean! Now it’s old. Now we need a negative bow! That’s the proof your boat is fast and modern! And, yeah, of course a crazy fat ass belongs in there!

    So we willingly accept that we design boats to fool ourselves. We buy boats because we want to satisfy our feelings. I’m a complete nerd, but I never let my emotional decisions be disturbed by annoying logic! Yes, it looks like a joke, but for me, and probably every human, it’s plain truth. The best use for logic is to use it to influence my emotional decisions into something that will last longer than just outside of the shop door. But no logic can make me do anything my emotions don’t like.

    So will the fat ass boats become a nightmare shortly after the boat is bought? No, mostly the buyers will love them for years. These boats do an awesome job for most of their owners, who sail very few or no ocean passages and close to never experience seriously bad weather. Their interiors are easily worth losing the big wave behavior they will almost never need. The readers of this site should probably look a bit more thoroughly at those priorities.

    So, am I writing all this just to say the obvious “different types of sailors need different types of boats”? Well…. yes… But I think some of the words on the way there might be worth it.

    I’m really bothered by how features that start as a rule tweak in a specific race class becomes standard issue in most sailing boats. I would love it if it was possible to go away from “how it was always done” (for some obscure reason) and rather look at what is the main need and what is the smartest compromise to get that. For long distance cruisers, I can safely say that negative bows should not be on the list. Neither should a long list of other features of normal cruising boats.
    PS
    In the near future, negative bows will be found on some cruisers.
    I’d be willing to bet a lot of money on that.

    • John Sep 6, 2018, 4:28 pm

      Hi Stein,

      Very good analysis, thank you.

      I would add one more thought to why taking ideas from extreme race boats like Open 60 and grafting them onto cruising boats is a bad idea:

      Because Open 60s and Volvo 65s are very fast and have elite navigators, they actually almost never experience the worst waves in a storm. Rather, they are fast enough to stay ahead of depressions and then veer off into less dangerous sea states before they get rolled by the depression and fall into the really dangerous areas on the back side with sudden violent wind shifts. Not saying they don’t sail in a lot of wind, they do, but they are generally not in anything like the worst sea state.

      No cruising boat can do this kind of sea state avoidance.

      (I didn’t figure this out myself, but rather learned it from Skip Novak who was talking about how much worse their weather experience was in the old Whitbread race where they were racing IOR Maxis capable of maybe 250 miles in a day, so they got rolled repeatedly.)

  • Matt Sep 6, 2018, 12:59 pm

    The importance of fore/aft balance is certainly neglected in many naval architecture circles, and – perhaps crucially – it’s neglected by the people who create the design tools.

    Most designers are aware of the need to get the form coefficients (most relevant here are Cp and Cwp) correct for the boat’s intended speed. There is surprisingly little room for variation here; if the correct Cp is 0.59, then designing the hull with Cp = 0.56 (visually indistinguishable to most eyes, until you overlay the two lines plans) will result in poor performance, and Cp = 0.53 will yield a lame dog.

    Only a handful of naval architects, Steve Dashew among them, clearly understand that it’s not just the whole-hull Cp that matters, but that forebody and afterbody Cp and Cwp must be considered separately as well. If the relationship between the two is not correct for both the speed *and* the intended sea state capability, the boat will have performance and handling issues in poor conditions. Most CAD software will not split them out automatically; you have to manually cut up the hull and hack the calculations a bit. Seakeeping calculation methods, too, exist but are often tedious to configure and not easy to use correctly.

    When there’s a strong push from marketing to maximize “boat per unit length” rather than “boat per unit mass” or “boat per dollar”, engineering generally isn’t going to push back without good quantitative data. That means both a better understanding of the characteristics that matter, and tools that are designed to reflect and enhance that understanding.

    • John Sep 6, 2018, 4:16 pm

      Hi Matt,

      That’s really interesting, particularly that the readily available tools don’t support this kind of refinement for sea keeping. As you say, and I had not thought of, makes it really hard for a designer to push back against marketing pressure to do something poor.

  • Eric Klem Sep 6, 2018, 2:14 pm

    Hi John,

    Agreed, this is definitely a good article. When I first read it I was surprised by the date on the images and checked in our log the next time I was on our boat and found that I had been about 80nm northwest of them with ~20-25 knots from the northeast and ~6-8′ waves (I anchored up around dark and got underway early the next morning so wasn’t actually underway at the exact time the pictures were taken). To me, this once again shows how small changes in location can have big effects, I was out there for fun and enjoyed myself while it would have been very different had I been where the Dashews were. Being north of the Cape, I had no SW swell so I didn’t have different wave trains interfering and the wind strength was also much more pleasant. I like the comparison they make to the 100 mile entrance pass, the ones that are only a mile are bad enough, I really don’t like the idea of a 100 mile one.

    I found his comments on loss of maneuverability interesting. They clearly had given thought to the possibility of a loss of steering and had wisely thought through the backup system. The seatbelts comment suggests that he feels the boat would have definitely made it through but also that they would have been incapable of accomplishing most tasks. For many boats where loss of propulsion or steering would present a truly dangerous situation if not dealt with quickly, it becomes crucial to be able to quickly switch tactics to the JSD or whatever the backup plan is both because of the vulnerability when beam on and also the horrendous motion that increases the length of time in that position.

    We saw Cochise underway for the first time earlier this summer in the calm waters of Penobscot Bay and it was definitely impressive how well it appeared to be moving through the water. In 2011, I was taking a 30′ ketch north in a strong afternoon southerly along the southern Maine coast and approached a boat that I just couldn’t figure out what it was until I saw it more in profile and realized it was Wind Horse. They were moving at a good clip going into a significant chop and what really drove home to me how well they were going was when someone stepped out on deck with an enormous camera lens to take pictures of the silly guy who was rolling his way north.

    Eric

    • John Sep 6, 2018, 4:38 pm

      Hi Eric,

      Very good point that even with all redundancy he has at his disposal in his boats, Steve is still constantly thinking and planning for the wild card event (like total power or steering failure) that can lead to disaster.

      I think each of us need to take the same approach to having a backup plan. For us it’s having a JSD ready to go whenever we go to sea: https://www.morganscloud.com/2013/06/01/jordan-series-drogue-launch-system/

  • Hippocampus Sep 7, 2018, 8:30 am

    Fascinating. But would also ask what impact gyradius and rocker have on boat behavior. I’ve sailed my beloved Outbound and have had opportunity to compare its ride to the current crop of production boats. Note less pounding upwind and less wandering downwind in difficult seas on the older Schumacher design than those with the flat, wide stern, slice of pizza boats. Have thought this is not only due to footprint but also relative lack of rocker and induced asymmetry of immersed hull when at heel in the newer offerings.
    Also note some hulls are more tolerant of weight in the ends and the slice of pizza boats seem particularly intolerant. Race boats seem quite diligent in keeping the ends light but this is often difficult for a cruising boat to do.

  • Jim Evans Sep 7, 2018, 2:06 pm

    All good points, both in the articles and the comments. As for Cochise, she’s the size of ( and nearly as ugly as) a small warship so you’d expect her to handle a bit of weather!
    As for hull forms, did Colin Archer get it right?

    • John Sep 7, 2018, 3:00 pm

      Sure, Colin Archer got it right…the same way Steve did: balanced ends.

      • Marc Dacey Sep 8, 2018, 11:48 pm

        Not that I can do much about the boat we have, but our steel motorsailer has a relatively short WL of 31 feet and an LOA of 42, with a cutaway forefoot, relatively bluff bows and a relatively narrow stern (about 6′ 6″ compared to 12′ 6″ maximum beam). These strike me as desirable traits in light of the discussion, even though I am resigned to heaving to (or running off with a JSD) when others might make a break for it in approaching bad weather. I endeavour to be careful about weight in the ends, even though my eye and our experience plowing down wave fronts suggests we have reserve buoyancy to spare, but we haven’t really tested conditions where stern buoyancy might come into play. So this is an interesting discussion in terms of “best tactics”.

  • Philip Wilkie Sep 7, 2018, 10:07 pm

    Our Australian Adams/Radford 40 is unfashionably narrow at the stern (LOA = 12m, Max beam is 3.66m, while the transom is 1.9m). Being an aft-cockpit design there is really only a crawl space from the companionway aft, and we keep pondering our rather modest storage space. Indeed everytime we step onto much fatter boats we tend to come away with a dose of boat envy.

    We haven’t sailed her much (I’m dealing to a host of leftover PO issues at the moment), but the two occasions we found ourselves surfing downwind (and ear-popping 13.5 knots was the peak, regularly topping 12 knots) it was like the proverbial running on rails.

    Reading this article, and the comments, makes me feel a lot happier about my ‘unfashionable backend’. Thanks.

    • John Sep 8, 2018, 12:36 pm

      Hi Philip,

      Glad to hear the piece made you feel better about your boat. Yes, interior envy is a dangerous thing…and a lot of how bad boats happen: https://www.morganscloud.com/2014/04/04/five-ways-that-bad-boats-happen-part-1/

      That said, I don’t think any of us are immune to it. But the more we go to sea in a good boat the more resistant we get to the dreaded disease.

      • Philip Wilkie Sep 8, 2018, 8:06 pm

        For what it’s worth the Adams 40 design shares a lot in common with the Adventure 40 concept; except it’s steel. They were a very popular barkyard build in the 80’s here in Australia. Ours was one of the later ones, completed professionally in 1991. The hull and rig are still in good condition, but as with so many older boats I have to replace the entire electrics and plumbing before I contemplate leaving sight of land. The list of ‘death traps’ and horrors I’ve uncovered so far seems to surprise no-one around here.

        Overall I’ll finish up spending about A$120,000 (purchase plus refit) to get a boat that’s 80-90% of an Adventure 40. And I’ll have no-one else to blame but myself for whatever goes wrong!

        • Marc Dacey Sep 8, 2018, 11:51 pm

          As the owner of a refitted steel cutter, I can honestly say that the inverse is true: you’ll have no one but yourself to congratulate when things don’t go wrong!

  • Stedem Wood Sep 8, 2018, 2:43 pm

    Hi John and Phyllis,

    Short of failure, worst-storm tactics for these boats is to motor slowly forward and actively dodge what you can in a cross-sea. I guess you need to add “keep the motor (and steering) turning” to your list of ultimate items for the safety of the boat.

    If, after getting the design right, adding redundancy, doing the maintenance, and learning the complex systems, something still goes wrong……….does your ultimate storm tactic of using a series drogue still apply for a boat the size of Cochise?

    Stedem Wood

    • John Sep 9, 2018, 12:05 pm

      Hi Stedem,

      Hum, I really don’t know. In fact I think you are far more qualified, after all your miles in an FPB 64, than I am. Do you carry any sort of drag device?

  • Dennis Harjamaa Sep 9, 2018, 6:58 pm

    Hello John,

    Great post like always. I thought I should comment on the remarks regarding the LRC58. My own boat Koti is still not fully finished, tools and loose paneling abound, which means I still have little first-hand experience in heavier weather. I wanted to make a measured and informed reply, so I got in touch with the delivery skipper Finn Topzand, who drove hull 2 “Broadsword” from Tahiti to the Bahamas, and more recently hull 4 “Raw” from NZ to Thailand. I made a point at asking him “Don’t hold back on any negative comments you may have”. Here is Finn’s unedited reply:

    “Having done 15000nm in the LRC58s in various conditions. I am of the opinion that the LRC is a good balance between the various compromises you have to make in boat design. We have been in a wide range of sea conditions up to Beaufort 11 on one occasion and more days than I would like in 7 and above.

    Through my experience I can tell you that the boat remains seaworthy, predictable and fairly controllable. If you are able to run dead downwind in the right conditions the LRC can provide a very exciting ride feeling like a big surfboard sitting on 14kts+ for long rides.

    We went right through the Great Barrier Reef to Darwin in May (which is when the reinforced trade winds are near the strongest) on board Raw (the latest dickey boat build). It was rare to be under 25kts and seeing 40kts wasn’t uncommon. The wind angle was aft of the beam 95% of the time. There is also some strong currents and 100nm+ of fetch was common. All making for a nasty sea state. Raw is equipped with paravanes which proved very effective when we were more than 30 degrees off dead down wind. The only reasons we put them away is because they slowed us down by a knot and I was worried about the loading if we surf down a wave.

    When we were under 30 degrees off dead Down the boat was a surprisingly straight runner. Occasionally a wave would pick her stern up and it would feel like a broach was coming but it never really did. My view is that while the long water line and sharp bow makes her prone to broaching, the stable flat hull and aft keel keep her on track and do a great job at minimising the effects.

    We had a Nespresso coffee machine sitting on the galley bench only secured by it’s rubber feet. It lasted 3500 miles before a one off wave caught us out and knocked it down. That must be some kind of indicator?

    From a seaworthy point of view I understand getting rid of the cockpit makes sense but it’s not designed as a commercial boat. The LRC is a home you can travel the world in. And most owners will spend a lot more time in a calm anchorage than they will in less than ideal conditions.

    We had the standard cockpit setup and it was a wet deck in a big sea but it was never more than 5cm deep and drained fairly quickly. The water on the deck caused no real concequence and after 4 days in lively conditions we had about 20l of water in the lazerettes.

    I have spent many hours dreaming of how to improve things on the LRC but as with every boat there is a compromise. I believe in the concept and think it has been very well executed. While it is not the perfect sea boat it is a great all rounder.

    Finn Topzand”

    You are quite correct that the 24m design being built in Turkey has a very different hull shape. She is a custom design for very experienced clients. This design should not be thought of as a big sister to the LRC58. I will expand the LRC family of designs as time allows, and they will reflect more of the thinking I have applied to the LRC58.

    Cheers, Dennis

    • John Sep 10, 2018, 8:12 am

      Hi Dennis,

      Thanks so much, that’s really useful. Sounds like the bow lock in, and then broach, risk that I was fussing about is far less of a problem than I thought it might be.

      Could you give us all some idea of why that is, design wise? Maybe a couple of paragraphs on how the parts of the hull work on each part of a big wave.

      Also, I totally hear and agree with Finn on the importance of being an all rounder and that many owners will benefit from the cockpit and justifiably take on the down-flood risk to get that benefit. That said, I still really like the no cockpit version you drew and I think I would still equip with a JSD.

      Great to hear that #4 is already out and about.

      • Dennis Harjamaa Sep 10, 2018, 8:59 pm

        John,

        Intuition would dictate that a fuller bow with ample reserve buoyancy must be able to resist a broach better than a sharp bow. I came up with a reason why this might not be the case after reading somewhere about the root cause of broaching, which from memory goes something like this:
        A boat stuffs her bow in a wave, moving the centre of lateral resistance (CLR that can be thought of as a pivot point) forward. At the same time the forward velocity decreases quickly and unless the forces are aligned along the vessel centreline the inertia will want to carry the centre of gravity past the pivot point. Think throwing a dart with the feathery end first.
        How best to counter this natural tendency that all boats have to a certain degree? It makes sense to me that a sharper bow without massive flare in the topsides would tend to keep moving without decelerating too quickly after encountering a wave. I also feel the sharp bow deflects the wave more gently. Imagine hitting pool balls at a sharp bow hull versus a fuller bow hull to get an idea which way the forces go and how much energy is absorbed by the hull.
        My thinking has always been that actual buoyancy is better than reserve buoyancy. By the time reserve buoyancy of a flared bow gets to work, the bow is already depressed in a wave, the brakes are on and the CG is about to overtake the CLR.
        This thinking has proven to work in practice not just on the LRC58 but on a number of sportfishing boats I have designed. These hulls have near plumb bows and much sharper waterline entries than more conventional planing hulls. Broaching has not been an issue and the hulls have a reputation of very comfortable riding characteristics, not to mention good fuel economy that comes from the waterline length/ relatively low displacement.
        What about hull balance then? A fat stern surely is just there to push the bow down?
        Instead of only looking at numbers such as the prismatic coefficient fore versus aft I also use ORCA 3D hydrostatics program a fair bit to visualise the effects of hull balance to the way the hull behaves with heel. I spent a fair bit of time playing with the hull shape in ORCA, heeling at various loading conditions. With the LRC58 I wanted to ensure that the forefoot pops out of the water soon after the hull starts to heel. Here it is also good to look at the shape of the heeled waterline planes. I like to compare these with the static waterplane to get an idea of hull behaviour with heel. With a bit of thought a hull can be drawn that has the tendency to go straight even if the aft of the hull has a higher prismatic than the bow, so we see that while numbers need to be right, they are not everything.
        Part of this equation is length to beam ratio, 4.9 at the waterline in the case of the LRC58. A skinny hull can have good balance with a bit more of a full stern than a beamy hull.
        Finally, adding a substantial keelson far aft will help ensure the bow keeps pointing where aimed. The size of the rudder is also important, as is the rudder profile. A proper NACA foil will steer far better than a flat plate.
        I agree fully that a hull needs to be well balanced fore and aft. Apart from the above checks in a hydrostatic program a good measure is the distance between the longitudinal centre of buoyancy (LCB) and the centre of the waterplane (CWP, which is considered the point about which a hull pitches) This number is about 4.5% of the waterline length on the LRC58, a bit more than the recommended 2% which would make one think that the boat will pitch wildly but this is not the case, she goes into a sea quite comfortably. Perhaps this recommended 2% is more significant in a sailing yacht scenario, where the inertia of the rig plays a big part in the pitching behaviour? I don’t know. (I believe I got the recommended 2% from Offshore Cruising Encyclopaedia by Dashew, there is a great diagram of a boat pivoting about the CWP with a spring in way of the LCG imparting the pithing moment. An excellent way to visualise the issue.)

        I have been thinking that it might not be a silly idea to carry a couple of large inflatable fenders onboard. I’m talking 0.8 mm diametre by 1.5m long type of size. These could effectively reduce the volume of the cockpit if properly inflated and tied down into the cockpit during passages where heavy following seas are to be expected. They might also come in handy at some docking situations.
        Could not agree more about having a JSD.

        Cheers, Dennis

        • John Sep 11, 2018, 8:42 am

          Hi Dennis,

          Great explanation, I even understood it, which does you credit!

          Very interesting about your experiments with ORCA on the healed hull. Would I be right in thinking that the chines have a substantial positive effect in this scenario?

          On the mast effect on pitching with sailboats. I can confirm that. One of the unexpected benefits of fitting a carbon mast to our boat, to replace the old and cracked aluminium one, is that she now motors up wind far better than she did, with much less pitching. This is not a small change, but almost miraculous.

      • Stein Varjord Sep 11, 2018, 6:24 am

        Hi Dennis.
        This is interesting reading. I have no experience with motorboats like the LRC58, but in the nineties I was racing some years in the extreme multihull classes in France and other places. We also designed and built some of them. (Formula 28 trimarans). From that experience, I think I can confirm some of your thoughts. This will be a bit too long to fit the quantity of the info I can provide, but I assume that some background is needed for all to get these somewhat esoteric issues.

        Until the early nineties, even the fastest multihulls had extremely sharp bows with very little buoyancy. Some compensated this with a higher bow. (The older Royale maxi cat is an exaggerated example.) For several reasons these multis don’t broach, but they certainly do capsize, and several of the same buoyancy and retardation issues play a role.

        When going very high speed at a reach, the relative wind is so far ahead that the sails are sheeted in quite hard, almost to full upwind position. This means the boats are flying on one hull and having ridiculous loads wherever one could imagine it. With some ocean waves, it’s a challenge to keep this going well, of course, so they are constantly at the limit of too much. This means that at over 30 knots, a very large number of live tests rack up quickly. Every wave… The older narrow bows meant relatively soft motion but every time one did a mistake, the bow would dig down deep with the deck far under water, the boat would crash to a full stop and, at best, turn slightly leewards before popping up accelerating again. Very close to capsize and the crew can mostly just watch and hope.

        The trimarans we built went to the opposite extreme with putting as much buoyancy as we possibly could as far forward and low as we possibly could. 1 meter aft of the bow and 10 cm from the bottom we had more than 3 times the width (and volume) of any of our competitors. (Still, this is very sharp bows, compared to monohulls.) Also we had rounded decks to shed the water easily. This worked just as we thought. When we were digging in too deep, the forward and sideways heel angles were still fine and the direction of motion was still parallel to the water surface, meaning that we could just ease off a slight bit and we got almost no retardation. We could push a lot harder, and the boat still behaved more predictably.

        The reason is, of course, just as in a motorboat at speed in big waves, that buoyancy is fairly useless if it’s only “reserve” buoyancy. It needs to work the whole time, or it might just as well not be there. If the bow needs to go deep to start lifting enough, its too late, because the angles are already wrong, retardation has started and things already have a momentum in directions we don’t want. It’s a chain reaction that is hard to stop when it has started, meaning that the solution lies in how to make sure it doesn’t start.

        I have zero experience with another issue you explain, that the bow pops out of the water at a fairly low heel. To me, this logically seems like an important feature. If a broach is starting, which means the boat is rotating, it must heel outwards in the turn and the bow pops out, fixing at least one problem. Thanks for teaching me new stuff and inspiring me to think!

        • John Sep 11, 2018, 8:58 am

          Hi Stein and Dennis,

          That’s interesting on reserve buoyancy. That said I’m still a fan, but I think it depends a lot on the hull type. In our case with a fairly traditional canoe type hull with relatively (for the type) fine ends, the reserve of flare and a bit of overhang seems to help. The big surprise is that in our kind of hull type, the moderate overhangs with balanced reserve buoyancy fore and aft seem to be a big positive to actually reduce pitching, pounding and bow lock in.

          The result is that McCurdy boats consistently beat theoretically faster boats in offshore races because the crew can keep driving the boat hard long after crew on more modern boats have backed off just because they can’t take the pounding and green water.

          That said, we are talking completely different types of boats here than the ones you are talking about, and the drawback of our type is that once real surfing starts we will never have the control that the boats you are talking about have. So at that point the only sane thing to do for us is stop and heave-to or deploy a JSD.

          For our boat that point, from experience, seems to be around sustained force 8. More on that in an upcoming post.

          • Stein Varjord Sep 11, 2018, 10:39 am

            Hi John.
            My statement about reserve buoyancy was easy to misunderstand, since I didn’t specify clearly what I think are its limitations. What I think you comment on is mainly this: “… buoyancy is fairly useless if it’s only “reserve buoyancy”. It needs to work the whole time, or it might just as well not be there…”

            I should have added: … but only when the speed is high enough to make the forces of momentum dominant. When the mass of the boat moves fast enough, changing its speed and/or direction will unleash lots of energy. If the sea doesn’t agree, bad things happen.

            I can’t give a specific speed where this momentum issue is prominent, but I’d say it’s rare for normal cruising sailboats. It starts to get relevant at maybe 10 knots, but doesn’t get dominant until quite a bit higher speeds are reached. Racing sailboats and fast motor cruising boats have to take it into account. Boats that are normally moving slower, but can easily surf at well over 15 knots, like the LRC58, must also consider this topic of momentum induced forces.

            At normal displacement speeds, reserve buoyancy definitely can do a useful job, but still I have some reservations. Looking at overhangs versus straight bow/ transom. If the deck has the same profile and length over all LOA is the same, a boat with overhangs has potentially much reserve buoyancy, but the boat with no overhangs has much more buoyancy in total. It has “filled in” the empty areas under the overhangs.

            The overhangs can be seen as high up floatation added to a shorter boat, or as low down floatation removed from the same length boat. I tend to prefer as much floatation as I can possibly get in the ends of a boat, (catamarans) and since length is normally limited, straight it is. Some flare is still needed, but as little as possible without getting slamming. I think a good attitude to reserve buoyancy on most sailing boats is to not make the boat bigger than what fits its length.

            The reserve buoyancy in the bow should maybe just be that the bow is long enough to easily carry its load. Probably no production cruising boat fits this criterium, since they are inflated as much as possible to create “value for money”, or translated to truth: To make it easy to sell from a brochure by listing all the stuff in the boat.

          • John Sep 12, 2018, 8:17 am

            Hi Stein,

            That makes sense and I think, based on my own experience with our boat getting difficult to control once surfing speeds exceed about 10-12 knots, that that speed might easily be the transition point where reserve buoyancy from flare and moderate overhangs stops being useful.

            That said, based on the racing success of McCurdy boats and our own experience in heavy weather, I think for most cruisers the softening of the motion imparted by well designed reserve buoyancy, coupled with symmetrical ends, is by far the most important criteria (after safety) to aim for. And in fact, better motion comfort can be a big contributor to safety, (and even going fast) particularly for short handed crews.

  • Stedem Wood Sep 9, 2018, 7:09 pm

    Boat came with a Galerider and para-anchor. I don’t consider the para-anchor a heavy-weather device. In many ways, using a drogue on a power boat is a different consideration than a sailing yacht.

    Biggest series drogue on the website is for 70,000 lb monohull. I can’t imagine dealing with the confusion of deploying and retrieving a series drogue long enough for something bigger than that.

    Most weather I’ve seen is short bouts of 50+ and days of 40+ Winds. Closer to the topic of your post, the hull shape, sturdy systems, big rudder and stabilizers means the boat can travel in just about any direction in those conditions. As mentioned in Dashew’s post, I wouldn’t want to have a steering or engine failure.

    A drogue seems a fall-back for failure because these boats lift their bow and run down-wind very well. If everything is working, the best storm tactic is to keep the boat moving where I’m going. Short of that I’d be moving in relation to the weather systems, timing landfall, or, last resort, running slowly into the weather and maneuvering in relation to the seas.

    I just don’t know what it would take to hold the stern into the weather if there were a problem.

    My best to you and Phyllis,

    Stedem Wood
    M/V Atlantis

    • John Sep 10, 2018, 8:03 am

      Hi Stedem,

      That’s interesting, and all makes sense to me, thank you. I totally agree with you on the para-anchor. Not a fan at all: https://www.morganscloud.com/2013/06/01/sea-anchor-system/

      I’m guessing that a series drogue would work, but as you say, the challenges of dealing with it on a 64 are intimidating. I’m thinking that to make it practical it would take a lot of customization including chain plates, a purpose built locker to deploy from, and a huge electric winch for retrieval.

      Given that capsize risk goes down exponentially at boat size goes up, and that you have a much more powerful backup engine than most motorboats, maybe not worth it.

  • steve holloway Sep 10, 2018, 8:04 am

    Great post as always, don’t pretend to understand most of it, but hey ho! good read anyway.
    What I wanted to say is that in all these discussions we tend to focus on off-shore sailing when in actual fact the vast majority of most peoples sailing is close to shore. Danger here is that this might lead you to think that if you’re not crossing the Atlantic regularly then having a boat with a big ass and a fin keel doesn’t matter.
    As an example take a peek at the video link below. This was a trip we did from France to the UK last week. Great conditions, 25 knots of wind on the beam all the way. Most boats, even badly designed ones would have had a good sail across the channel the ‘off-shore bit’ no problem, but the video is from the 5 mile or so stretch passing Cap de la Hauge where the tide gives you some interesting waves.
    For us in a 26 ton long keeled canoe sterned boat it was a bit of fun, but in anything other than that it would be somewhere between uncomfortable and dangerous.
    So for those who think ‘I needn’t worry I’m not crossing oceans,’ I’ld say think again!
    Steve
    https://vimeo.com/289058806
    P.S. even in our boat the steepness of the waves managed to stuff the bow sprit into the water so hard it broke a 26mm teak plank in half. You can see how even our 26ton boat with really good weight distribution is hobby horsing in the video, I really do feel most production boats would have struggled with this.

    • John Sep 10, 2018, 9:54 am

      Hi Steve,

      A very good point. The only thing I would disagree with is that a long keel is required for seaworthiness. This comes up a lot, but it’s not, in fact, true. Fin keel boats can be perfectly seaworthy and in fact properly designed ones can actually track better and steer much easier than full keel boats with attached rudders.

      Not saying that fins are better than full keel, just that there are good sea boats with both keel configurations.

      • Steve Holloway Sep 10, 2018, 11:59 am

        Yes of course, I wasn’t trying to suggest fin keeled boats can’t make good blue water boats I’m sure a well designed one can perform well and have the additional advantage of being intrinsically faster, easier to manoeuvre etc. than a full keel.
        Having said that I wouldn’t swap my keel hung rudder just for the protection it gets for being mounted that way.
        Steve

  • Dennis Harjamaa Sep 11, 2018, 8:43 pm

    Hello Stein and John,

    Very interesting about the high performance trimarans. They are indeed a complex equation to get right. No point even trying to start designing one without extensive sailing experience on a variety of boats. I was very keen to learn about multihulls back in the early nineties when I went to boatbuilding and design schools in Maine. Unfortunately at the time there was little information readily available, so I sent out for design catalogues from all the designers I could find around the world, Wharram, Newick, Simpson and Graigner from Australia just to mention a few. Many of these design catalogues had great information on building techniques as well, so very valuable for a budding designer to study. Needless to say that having Dick Newick come to give us a lecture at the Landing School was rather exciting! I also jumped at a chance to go and do a two week internship at Gold Coast Yachts in the Virgin Islands, they build great daycharter cats in timber, wing mast and all. I learned a lot about strip planked construction there. The fact that this was in February was an icing on the cake, Maine is a bit bleak that time of the year…

    Unfortunately I got few opportunities sailing on multihulls but I go on about my early fondness to the type because it probably explains why I like lighter boats.

    I believe it was an article by Rodger Martin that got me thinking about the forefoot popping above the waterline at heel being a good safety feature to have going downwind. This is of course easier to achieve when the hull is light.

    What comes to chines, I think that the effect they have on hull balance is likely much less pronounced on narrow boats.

    I can imagine that going for a lighter rig would have paid massive dividends in the pitching motion on Morganscloud.

    Unlike on a sailboat, on a motorboat the longitudinal pitching moment is not perhaps best minimized, adjustable would be ideal, and fairly easily achievable with ballast tanks in the very bow and stern. I have no experience with this of course but I would like to experiment , thinking that slowing the rate a boat pitches when punching into waves would add to comfort levels onboard, could well reduce drag, as well as perhaps keep the flow of water cleaner around the propeller.

    I wonder whether a fuller stern that bobs up and down less might have a similar smoothing effect to flow around the prop?

    OK, I’m just thinking aloud here, but goes to show these is all a complex issues, no absolute right answers, and a good reason to keep designing boats!

    Cheers, Dennis

  • Giles Adams Sep 12, 2018, 5:22 am

    Hi Dennis,

    Where is your current thinking on the provision of stability devices for the LRC58? If I recall you have two now with nothing built in, one with active stabilisers and the latest with paravanes.

    With the current topic, what would you do about active stability?

    Regards

    Giles

    • Dennis Harjamaa Sep 12, 2018, 5:59 pm

      Hi Giles,

      Judging from comments from Finn and the owners of Raw, as well as Rob, I would recommend either active fins or paravanes, depending on personal preference. Both systems seem to reduce motion a fair bit. Everyone who has made inquiries is looking at one or the other, the current twin engine build in Holland will likely have a pair of Sidepower Vector fins, which look very interesting with their curved fins.

      I will add a pair of paravanes for Koti (I got the plans for the fish from Michael Kasten) at some stage before heading offshore, my first mate suffers from seasickness so everything I can do to help on that front will be worthwhile.

      Cheers, Dennis

      • John Sep 13, 2018, 8:03 am

        Hi Dennis,

        That’s interesting. Having motored a great deal over the years in a sailboat with no stabilization when it’s calm, I would definitely be wanting stabilization. On balance I think I would go for paravanes over active fins because of the vulnerability of the latter, particularly on a shallow hull like the LRC 58. Rob sent me a drawing of the hull with the fins he fitted and my first thought was “I wonder how long it will be before one of those gets wiped off by even a brush with the bottom?”.

        • Dennis Harjamaa Sep 13, 2018, 7:48 pm

          Hi John,

          True, paravanes will be much less prone to damage, will cost less to install and to maintain than any other system. These are strong arguments for paravanes over fins in my book.

          Installing fins to a shallow hull is going to leave them more exposed than in a deep hull for sure. Still, we have seen that even in deeper hulls the fins are not guaranteed to be safe in a grounding or being hit by logs etc. Accidents happen and no appendage protruding from a hull is totally safe, including propellers and rudders.

          The Magnus effect rotor type stabilizers are very interesting. I got a chance to go out on a boat with the Magnusmaster system installed when I visited Holland about a year go. We only went out to inland waters where the rotors were being tested on a newly launched heavy steel Dutch cruiser so I did not experience dampening in waves, but the ability of the rotors to “manually” induce a severe roll and then dampen it to zero was very impressive. The rotors have the benefit of folding back when not in use so will be less prone to hitting things than fins. Some installations have the rotors mounted through the transom which gets them totally out of harms way when not deployed. Unlike fins the rotors will not cause a steering effect even if mounted close to the transom.

          So there are plenty of options out there for stabilization, all with their pros and cons.

          Cheers, Dennis

  • Henry Rech Oct 5, 2018, 10:23 am

    Any thoughts on stern water ballast tanks when running? Stern down, bow up.

    What about single stabilizer fin embedded in slot in keel, located at turning centre of vessel (for minimal impact on helm)? The fin would always be protected.

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