Flat bottom/vertical sides/flat deck/ flat everything

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

  1. Ron Cook
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    Ron Cook Junior Member

    Stronger Grasp

    I am a professional boat builder over the years I have designed, engineered, built and structurally repaired and re-built many flat panel high speed craft. I'd say I have an exceptional grasp of the problems.

    I respect your criticism. Since you don't think my hull shape is right please draw up what you think is better in a box section 60 footer and post it. I stand by the rig.
     
  2. PAR
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    PAR Yacht Designer/Builder

    I wasn't trying to insult you Ron. I just wouldn't consider a box boat of those dimensions, for several reasons, some of which I mentioned.

    If I was to consider a 60' sled and keep the hull form simple, easy to build, have a high performance potential, be inherently strong, minimum wetted surface, etc. this would be more in keeping with an absurd, but fast craft. It only wants to do one thing, but it would quite well and it's an inherently strong form that presents better lines to it's intended use, without the weight and frictional drag penalties of a box hull.

    The Santa Cruz 70 and similar boats have tried the huge Laser idea already. It works if it's kept light and the bow doesn't have quite the bluffness of the dinghy.

    This one is 60' on deck on a 59' 2.5" LWL. No sense wasting LWL to over hangs.
     

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  3. Ron Cook
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    Ron Cook Junior Member

    Lines

    Par, Very nice you have a wild side too. I find extremes more fun to play with.
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    I'll try to pick up the gauntlet, Ron. Yes, I know there is far more risk in suggesting an idea than in criticising someone else's! Also I lack a sailboat, something I am about to rectify, so I'm not yet speaking from experience, therefore commenting in areas other than construction is probably living dangerously. But here goes.

    At first glance I thought the design was for a much smaller boat. My inclination would be to scale it down to about 15 ft and try it out. That would simplify the construction challenges and speed up hull design evolution.

    I think it might develop excessive weather helm as it heeled, and possibly have a tendency to pitchpole as the rocker increases unless the bow is raised by the sail lift. A Vee bottom might fix that and reduce pounding too, if it were a problem. With the mast aft rig, and the way the CoE shifts forward when reefed, the deeper forefoot might also help it stay balanced. With a small boat it would be fairly easy to rip off the bottom and try something different.

    The twin retractable keels are of interest. However, with a flat bottom the boat should not need them to remain upright when aground.
     
  5. sharpii2
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    sharpii2 Senior Member

    It's interesting to see how much controversy this design has raised.

    Hat it is is essentially a very big sharpie with working sharpie style low free board.

    A big problem with such low sides is that the boat may want to stay inverted if capsized. That and all the wire to hold up the mast may prove enough roll dampening keep it upside down.

    When Bolger tried that rig, he was successful because he knew what he was dealing with. He was dealing with massive rigging loads to hold the luff of the huge jib tight which were transmitted directly to the hull.

    His answer was to install massive chines and sheer clamps to resist the loads.

    It worked.

    He said that the boat could sail closer to the wind than just about anything else. The problem was that it required undivided attention by the skipper to get the sheeting just right. Without that, the boat was actually much slower.

    He also said that this was about the most expensive way to put sail on a boat that he had ever used. The bang was good, but the bang for the buck was not.

    Add to that the fact that this rig will probably have relatively poor sheeting for reaching (like just about any boomless rig) and you end up with with a package that is probably an excellent up wind sailing machine, but mediocre in just about everything else. Also, I see no way to increase the sail area for light winds, except for going down wind ( a very large chute)

    As for the hull. I think the hull might have too much initial stability which may not allow it to heel enough in light to moderate winds to reduce pounding. You might need ballast tanks to initiate heel in those conditions. Such tanks could also be used to help right the boat if it capsizes, but they would have to be huge in order to do so.

    I once had a 10 ft scow that had a sloop rig with the mast way aft, so the jib was by far the largest sail (55 sf out of 85 sf). The designer put that jib on a long boom with the pivot point well aft of the leading edge. The pivot point was nothing but a hold down which attached to the deck.

    The sail was quite effective on all points of sail. It had such low sheeting tensions that I ended up removing the sheet line altogether, only to discover the sail was self adjusting to the wind. From that point on, the boat had only a main sheet. And this was a cheap rig for a cheap boat. It had a 2x4 for a mast and four steel cable stays.

    Such a jib might be far too daring on your concept. The boom would have to be cocked up considerably which would rob sail area.
     
  6. PAR
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    PAR Yacht Designer/Builder

    For what it's worth Ron, I'm playing with a test bed of similar shape, though 1/4" scale of the image above. I does everything poorly, except plane off, which it does just by exhaling on the sail. It's "uni" rigged with a sock luff, which will soon be converted to a semi rigid wing luff.

    I've found extremes are only fun if you have a client that doesn't mind taking a bath. Unfortunately I don't have enough of these, so a generally more conservative approach is desirable. To date all my designs have floated with the decks facing up on launch day, which is probably the sign of a chicken, but more then one has promptly capsized when pressed in the first good breeze it saw.

    Bolger's efforts in his box boats was to provide as much initial stability in small craft as possible. He also desired interior volume and simplicity for home construction which the box sectioned hull forms offered. On a 60' yacht, particularly one designed for performance, the wetted area of the box section alone, would make me tend toward different shapes.

    I have no doubt a 60' SunFish would be fast off wind, but would you really want to be in one for more then a few hours.
     
  7. sharpii2
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    sharpii2 Senior Member

    Nice power boat hull, PAR.

    I wonder about that dragging transom under sail.

    When you're not planing, you're dragging.

    I could imagine this hull with relatively low cabin and a pair of modest outboards, sipping along at maybe 15 to 20 kts, with a modest sail, perhaps, for supplemental power.

    As for a pure sailboat, I would take the sharpie hull over yours. I bet the supposed draggy sharp chines are nothing compared to that draggy transom.
     
  8. Ron Cook
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    Ron Cook Junior Member

    Bolger photo

    I have tried to upload this picture before without success. The file may be to big?
     
  9. Ron Cook
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    Ron Cook Junior Member

    Did not upload

    Since the picture did not upload here is a 40' version I drew last year. We all had so much fun with the 60'er, at least I did ha ha.

    Have fun guys
     

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  10. Tanton
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    Tanton Senior Member

    Here is a " Box Boat" that I designed for a French builder. The surprise came, that assuming the apparent simplicity of a Bolger type of boat, she was far more complicated to design and build that it first appeared.
     

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  11. Ron Cook
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    Ron Cook Junior Member

    Hope this time is a charm

    Phil Bolgers 24' Corsair
     

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  12. PAR
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    PAR Yacht Designer/Builder

    I think you'll find that the shape above is well suited for her intent. Sure at displacement speeds she's a tail dragging pig, but frankly, she planes upwind in nearly any excuse of a breeze. The quarter scale version is less then 200 pounds full up on a 15' LWL and carries more then ample horsepower with her upwind rig (160 sq. ft.). Down wind she takes no prisoners with a 60% increase in sail area. This hull shape has no noticeable hump and just leaves her stern wave behind without shifting weight or pumping anything.

    She's quite tender as you'd imagine with those sections, but in reality her transom isn't as immersed as it might appear. As soon as the rig fills, she's on her flanks, the leeward chine lightly immersed and the windward chine and transom flat clear. This shape isn't that radical. I know of quite a few dinghies with similar shapes, some have hiking wings built in, others like mine, have separate wings (an aluminum tubing after thought, once I'd eaten enough water).
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

    PAR, did you put a paper jet on steroids?
     
  14. PAR
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    PAR Yacht Designer/Builder

    My design pre-dates Paper Jet by a few years, but they are similar. Paper Jet has built in wings, a deeper forefoot and a bluffer bow. The beam to length ratio is different, but both boats use extreme topside flare. My test bed is also 15% longer and 20% heavier.

    The proposed 60' absurdity above, is pure fantasy, though imagining sled rides in the roaring 40's can be entertaining. You're always going upwind in a boat like this.
     

  15. chabrenas
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    chabrenas Mike K-H

    1. If you want to build a hull like this with a thin skin that does not 'pant' between stringers & frames, make the frames curved, not slabsided. Forcing some double curvature into the skin will stress it and make it rigid in its own right.

    2. The rig has quite a bit in common with the lateen sail of a dhow or an African outrigger canoe, which works very well indeed. Does anyone know of any attempts to build a dhow rig from modern materials? It has the disadvantage in enclosed waters of having to be gybed rather than tacked (the halyard exits the mast forward, and the yard flies over the top of the mast during a gybe), but it is very easy to handle.
     
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