Flat bottom/vertical sides/flat deck/ flat everything

Discussion in 'Sailboats' started by Ron Cook, Apr 3, 2009.

  1. sharpii2
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    sharpii2 Senior Member

    So. At least I was right about one thing. Your hull needs a lot of horsepower to work (for a sailboat, that is)

    I just don't see how it is an improvement on this gentleman's sharpie hull. It seems designed for an entirely different purpose. The much smaller Jib only rig would be the equivalent of, say, 100sf or less on your 17 footer. Except in a fresh breeze, your hull would be a pig with that amount of sail. (S/D of 35 vs 56, approximately)

    The sharpie shown would be doing a lot of displacement sailing as well as the planing variety.
  2. Paul B

    Paul B Previous Member

    I've done a quick 3D model of your idea. I'm posting jpegs of the bottom view and a 3/4 view from the stern.

    Regardless of the ease or issues with building this box strong enough, this shape is a wetted area monster and would not do well uphill in any conditions, and would be sucking along the ocean downhill.

    I don't think the "wedge of cheese" shape proposed is any better, maybe worse in a 60' size.

    I would say the rig is well matched to the hull, neither is very efficient.

    My feeling has always been the process of building a boat is a long and difficult endeavor. The result should be something great. Putting in the effort and ending up with something not-so-good doesn't seem to be a good use of time.

    Attached Files:

  3. PAR
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    PAR Yacht Designer/Builder

    Sharpii2, the boat is 15' not 17' and my upwind SA/D is 52.5 with me in it. That's plenty of power. Down wind the SA/D is absurd, but fun if you can keep it upright.

    I'm not suggesting this is a better shape, but if I was to build an absurd 60' sled, I'd want an absurd sled that was likely to perform well beyond the potential of the box hull as well as be inherently stronger, lighter and of course the performance potential.

    In reality my test bed doesn't sail at displacement speeds for very long (a few seconds). It begins to lift as soon as you start moving. The transition is humpless, in fact you don't even know it happened unless you look astern and see the wave depart the transom. It accelerates very quickly and in light air.

    Is it a practical boat, no, but it is a fun boat. It's not as radical as some of the dinghies I've sailed and seen in recent years, but it's well above the middle of the road.

    Paul B has it about right, in that neither is very well suited for a 60' ocean capable craft, nor are they particularly efficient.
  4. sharpii2
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    sharpii2 Senior Member

    Just how much more whetted area would you say it would have? 10%? 15%?

    And wouldn't that hamper it primarily in light wind conditions?

    My guess is that the chine digging in might actually improve upwind performance.

    My improvement of the boat would be to go to a double chine flat bottomed approach, where the bottom piece would be about one third the width of the boat and the rise from the bottom chine to the top chine would be kept constant. This way the piece shapes would be quite predictable. This would whittle away at the extra whetted area and improve the bottom stiffness. Perhaps the added shape complexity would be offset by less structural bracing complexity.
  5. yachty4000
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    yachty4000 Junior Member

    There is an IMOCA 60 built of flat panels I believe it was called Furtif (FRA 60). It has more panel than your design there no real justification for doing a box as it seakeeping wouldn't be good. The reason for it is you don't need a mould so it is cheap as you just lay up flat panels and bond it together like an overgrown Mirror dinghy.
  6. ancient kayaker
    Joined: Aug 2006
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    ancient kayaker aka Terry Haines

    I am planning a small sailing kayak for this year which will have a plastic lateen sail. There is no mast, the aluminum boom will be mounted at the bow, so there is no problem when gybing or tacking. However, it is not likely to have a great performance due to the shortcomings of a hull designed for paddling not sailing.
    Last edited: Apr 10, 2009
  7. Tanton
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    Tanton Senior Member

    Open 60 with CPC, composite panels construction. Just as simple as it can be!
    Method, also used on Tango(s) Class 40 and Class(e) 950.

    Attached Files:

  8. Daniel Noyes
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    Daniel Noyes Junior Member

    Hi all
    As a builder I think 90 degree angles and flat pannels are a false economy. 2 reasons, the hull is about one third of the work that goes into building a boat so you still need to build a good mast, foils, rigging, etc and for just a tiny percentage more work you can have a nice hull.
    also it take about as long to cut a straight line or frame up a 90 degree angle as it does a curve or another angle and if something has curve or od angles mistakes are actually harder to see, the eye is great at telling if a flat pannel isnt flat or a 90 degree is just off but curves are much more forgiving, I think often times beginning builders think that because it looks boxy it will be easier to make...not necessarily.
  9. Paul B

    Paul B Previous Member

    Designs like this really confuse me.

    The only raison d'etre for an Open 60, Open 40 is to win races.

    The design shown would not be competitive in the class.

    So why would such a design exist?
  10. bistros

    bistros Previous Member

    For the same reason Doug builds his "foilers". Because people who think they know a lot have a lot more confidence than they should. To this kind of person, science, education and experience are impediments to their quest, not help.

    There is no point in arguing with them, they will soon be relieved of excess time, money and reputation.

    Perhaps in this case we will gain another on-line "expert" to contribute to design discussions for years once he abandons this idea and catches on to Doug's scheme.

  11. Paul B

    Paul B Previous Member

    I was not referring to Ron's boxboat or even to PAR's wedge of cheese. I was specifically referring to Tanton's drawing. I can see where amateurs like you or I or Ron or PAR might draw up something silly. I can't imagine a well known design office doing something like this.

    I know the old adage, if the customer asks we can do it. However, I know there are many professional offices where this sort of project would get no more than 5 minutes of discussion before the client would either listen to reason or would be shown the door. It doesn't do the firm's reputation any good to produce plans for a project that does not have any chance of success.

    It puzzles me that something like this ever gets into a sketch.
  12. sharpii2
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    sharpii2 Senior Member

    Back to Ron's design.

    Phil Bolger drew something similar to this years ago. The only difference was his was double ended and had a level chine, aft amidships.

    His was a 31 footer to be powered by a single leg-o-mutton sail and to use water ballast. It had a dagger board and a retractable rudder.

    The sail area was small in proportion to the displacement.

    As silly as it may sound, Phil thought his design could cross an ocean.

    I would think the biggest criticism of Ron's design is its inconsistency.

    With the straight sides and flat bottom, why the angled retractable keels?

    And why so deep?

    Wouldn't the wide, flat bottom provide sailing stiffness that these deep keels seem designed for? Lifting ballast keels, IMHO, add tremendously to cost and complexity. Why go through all that for a cheap simple hull? I could almost see one or two sing keels that could lock down as being more simple and less likely to jamb.

    The rig I can understand. It's an experiment. And IMHO a worthy one. Not for performance sailing so much as for cruising.

    All in all, I feel inclined to take Ron at his word that he could make it strong enough to take the thrashing its likely to get. I am also inclined to say that the design could work reasonably well if sailed with a degree of caution.

    My big worry would be of a capsize. I think it would be less likely to right itself with two keels than with one just as deep. The thought being that the two heavy weights so far out to the sides would add considerable roll dampening inertia. Right side up, this might be a good thing. Upside down, very much not so. The drag of all that standing rigging underwater plus the roll dampening inertia of those two side keels may keep the same waves that capsize her from righting her later.

    Like many of today's open 60's she would have to be sailed in mind that she could capsize and never recover.
  13. Ron Cook
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    Ron Cook Junior Member

    As far as wetted surface goes the box section in a 60’er displacing 22,300 lbs is
    459 sq. ft. and a 60’er with round sections of the same displacement the wetted surface is 429 sq. ft. That means the box section has 6.54% more wetted surface.

    When both boats are heeled 15 degrees the round section one will have 412 sq. ft of wetted surface and the box section will have 417 sq. ft. of wetted surface which is 1.2% greater for the same lwl length.

    My educated guess is that the box section hull would be significantly easier and quicker and cheaper to produce that it deserves a serious look.

    With the aft rig the box section would be a going to weather machine. The key to the performance is to keep the chine razor sharp.

    Y-M-T what is the wetted surface area on your open 60 design? Neat boat. When your design is heeled 15 degrees is not presenting flat panels to the water looks like it may pound.

    Attached Files:

  14. sharpii2
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    sharpii2 Senior Member

    I am not surprised.

    The shallower the bottom, the less difference in surface area between rounded sections and straight sections.

    I know this by personal experimentation with section shapes, all having the same area.

    It is true, however, that the dead flat section with dead vertical sides IS going to have the most area. But as the Width/depth ratio grows, this becomes less and less significant.

    IMHO, from some experience with a boat with a very high Width/Depth ratio, rounded sections do little to relieve pounding when sailing up wind.

  15. Paul B

    Paul B Previous Member

    I think you need to check your calculations. Displacement for displacement, a triangle section should not have less wetted area than a semi-circular section.

    I think you will find this to be untrue.
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