A beamy 23 ft sailboat idea

Discussion in 'Boat Design' started by John Smithson, Aug 25, 2021.

  1. John Smithson
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    John Smithson Junior Member

    I've adjusted it since then to have a smaller bottom portion. The water line I would expect higher and have it sit stable. I wonder if this shape would cause pounding? Trying to strike some balance between a flat hull and something with a bilge and thinner hull shape in the water (though maybe misguided?).

    [​IMG]
     
  2. gonzo
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    gonzo Senior Member

    What are the convex sections for?
     
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  3. John Smithson
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    John Smithson Junior Member

    Mostly just (possibly misguided) intuition.

    What I was thinking is that as the boat heels, the side coming out of the water will surrender less buoyancy than a straight V shape would. So the heeling down side wouldn't need to take up more of that weight and be forced down into the water further than it has to.

    It seems like the side heeling down would basically have the same increase in buoyancy as a straight V shape would have from a flat position.
    [​IMG]
     
  4. bruceb
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    bruceb Senior Member

    John, (or anyone else), I have an unfinished fiberglass hull and deck, 9' x 23', shaped much like that that is free to anyone that wants it in Atlanta Ga.
    No extra bump on the bottom though. It was a reasonably successful MORC design in about 1980, I had a complete one that I raced and bought this one expecting to complete it as a race boat but the rules changed and I never finished it. The actual design was a Mirage 236/Kelly 24. This was before the Mini's, but shared the same ideas, just not as extreme. I sailed my first one a lot, we did some coastal races with it and also used it as a mini cruiser so I have experience with it in a lot of different conditions and I have developed respect for short fat boats. As long as they are not too heavy, they have very good performance for their size and they have room for a workable interior. Mine handled 8' waves and 25+ kts of wind upwind and down and kept the crew reasonably dry and comfortable since it tends to ride over the waves instead of through them.
    Bruce
     
  5. wet feet
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    wet feet Senior Member

    The same quantity of materials would produce a much better boat if rearranged in normal proportions i.e. a length/beam ratio of around 3:1.The longer waterline would ensure more speed and there may even be a reduction in wetted surface.If being afloat soon in a beamy boat is the desire,a trip to France to buy a Mini Transat a generation beyond being fully competitive would do the job.They are required to be self righting and have water ballast as well, then there is the advantage of having the potential to travel about twice as fast as the heavy displacement alternative at peak speeds.
    [​IMG]
     
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  6. John Smithson
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    John Smithson Junior Member

    I think it depends on a persons priorities.

    Speed isn't at the top of what I'm looking for (though I find it really interesting how these beamy boats are such speed demons when they oversize their sail layout. Which makes me think perhaps beamy isn't the harsh speed sacrifice people say it would be).

    I'm looking for a boat that has a very shallow draft (capable of going down a river), while also having a large carrying capacity and decent living area for a single hander.

    Also manageable for 1 person and more comfortable at sea (less heeling) while able to get close to an average cruising speed of 4 knots+ under sail.

    I admire what people like Sven Yrvind is doing, though his average of 2 knots and such cramped living space I could do without.
     
  7. Dolfiman
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    Dolfiman Senior Member

    L/B = 1,5 is really "too much", I mean really too small to do a minimum decent sailboat, but L/B = 2 to 2,2 could be feasible, i.e. B 3,2 to 3,5 m for L 7 m. You can have a look at this micro cruiser design, Cartoon 400, and try to extrapolate it to L 7 m with this proportion :
    CartOOn400 - Vincent Lebailly Yacht Design : Voilier construction amateur https://www.vincentlebailly.fr/cartoon400-voilier-construction-amateur/
    It is a full daggerboard with draft mini 0,15 m / maxi 1,20 m and twin retractable rudders.
    About the stability, no info on the ballast, just said that it is certified for a Cat C classification. With such proportion and a retractable daggerboard, you have no chance for a better classification. To reach B or A with a small cruiser, you need a special attention on the stability / knock down, meaning among other things a keel with a quite important draft and a lead bulb at the tip end, and not too much beam because, although that gives more stability in the small heel angles (< 25 deg) , that also tends to decrease the AVS (angle of vanishing stability) in the 110-120 deg zone.
     
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  8. Milehog
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    Milehog Clever Quip

    IMO by obsessing on "less heeling" you are creating a slow, ill handling and hard to build vessel.
    If you insist on this hull form build a model then a dinghy to the same proportions first.
     
  9. gonzo
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    gonzo Senior Member

    If you are looking at very shallow draft, convex sections are not good; they increase draft. The shallowest draft would be a flat bottom.
     
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  10. wet feet
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    wet feet Senior Member

    Just to fill in some gaps,could we see a side view and a frontal view showing the devices that limit leeway-i.e. a keel or centreboard.I wouldn't mind seeing a pic or two of the OP's last boatbuilding project either as it would allow us to gauge his chances of dealing with some of the complexities of an extreme shape.A brief description of the proposed building technique might also be helpful.
     
  11. John Smithson
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    John Smithson Junior Member

    I took a stab at adjusting the dimensions towards a catboat (closer at least). Dropping the beam down to 14 ft, and the length up to 26 ft. So just 8% more beam than some catboats have.

    Probably would want longer bilge keels, put them in quickly at the end here. The main thing is a drop down keel.

    [​IMG]

    Plywood framing (CNC or templates should produce accurate to the cad designs). Still undecided on what type of GRP core to use. Cedar strip maybe? Seems like it might be easier to get these shapes while not running into the extreme costs of trying to do foam for the entire thing, then all fiberglassed in (of course).

    The extra room on the designs gives a lot of space to set aside for filling with foam to keep the entire thing in positive buoyancy for added safety. The main thing is getting the keel weight right and other measures for self righting (active ballast? Even mast buoyancy), if even possible with such a wide beam. But smaller boat I would think would have an easier time at it.

    Anyhow, just the general idea. Obviously still just ideas from a random non naval architect... so, it's worth about that much....
     
  12. wet feet
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    wet feet Senior Member

    Looking more practical, but a couple of thoughts occur. First of all that amount of immersed transom is likely to add quite a bit of drag and I would encourage you to look at the sail area/wetted surface ratios for existing designs. Second, you might find that the extreme compound curvature aft will be quite challenging to create. Building a model prior to building is almost always a good idea.
     
  13. upchurchmr
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    upchurchmr Senior Member

    You're not going to like the very small cockpit and the seat across the back will be useless.
    Get rid of the bilge keels, they add nothing but drag. Unless you are in an area where the tides dry out a great deal of area.

    Keep going, you will get back to a more normal boat when you finally look at the reasons for current design, and understand the limitations of extreme design.

    Perhaps you should take some sailing lessons. Some real understanding will help.
     
  14. bajansailor
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    bajansailor Marine Surveyor

    John, all of the hard design work has been done for you with the evolution of the Mini Transat boats - just select a stage in the evolution that you like, and use that as a basis for your design.
    They started off originally as fairly standard / conventional small sailing boats, and then gradually evolved to the scows that we see today.
    I see that you are in Kansas - would you be planning on sailing this boat on a lake in Kansas, or will you be moving elsewhere with it?
     

  15. John Smithson
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    John Smithson Junior Member

    I looked at them, but they don't seem very livable. 21 feet long doesn't give much to work with.

    If I'm to build a boat, then I'd need to take it down the Missouri river into the Mississippi. Which is why I'm more concerned with draft. My goal is cruising to far flung destinations.

    I could "money" myself a boat, but it just doesn't compare to the narrative of a person from Kansas building their own boat of their own design and sailing it off as everyone laughs "that's impossible! You can't do that!".

    The cockpit is 5.8' by 9', so smaller length wise... but width seems rather roomy to me. Though it does need more thinking through (the big open center with such width doesn't seem ideal).

    Haha very possible. Though the newer one isn't that far off from a catboats dimensions.
     
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