"Picnic Boat" Hull shapes

Discussion in 'Boat Design' started by Guest, Jul 15, 2001.

  1. Stephen Ditmore
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    Stephen Ditmore Senior Member

    You might want to check out the work of Doug Zurn of Marblehead, the Midnight Lace designs of Tom Fexas, and the new Dave Gerr design from Santa Cruz yachts, as well as the Hinkley.

    By "monohedron" Tad means a shape where the deadrise remains constant.

    I've done some work for Harry Schoell, and remain fond of his method of blending a fine bow into a monohedron bottom. This is described in a U.S. patent that is now public domain.
     
  2. gonzo
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    gonzo Senior Member

    Do you know the Patent number?
     
  3. Willallison
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    Willallison Senior Member

    Tad:

    Thanks for the description - I'll try to convert them into a preliminary type sketch and see what I come with....
    As far as the boats relationship to others of similar appearance - if not form - I'm interested in them all ! Aussie designers Murray, Burns & Dovell ( http://www.murrayburnsdovell.com.au/power.htm ) for instance penned the Palm Beach motor yacht range - conventional shaft driven boats with a much lower speed range than the Hinkley, but still in the 'picnic boat' mould.

    Stephen:

    Thanks for the other leads - if you've a read a few of my other posts, you'll know I'm a bit of a Fexas fan - but trying to find drawings of his work has so far proved impossible.
    I've read a little about the Santa Cruz - though I must say I'm not a big fan of some of its styling.
    Doug Zurn is a new one to me - I'll do a little searching and see what I can come up with.
    I've looked very briefly at the Schoell patent some time ago - sorry Gonzo, dunno the number - probably time I took another look....
     
  4. Tad
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    Tad Boat Designer

    Will.....

    The Murry/Burns/Dovell boats are interesting. They apear to be using a round bottomed hull. They certainly must be when they claim "The hull shape is a development from the British destroyer hull lines, and will perform significantly better in rough water than contemporary cathedral style hull forms" Oakkkay.......???

    They claim 20 knots for the Kennedy 30, but 30 knots for the Palm Beach 38, which will be fast, and very wet, in a round bottomed boat. The 38 seems to be lacking any spray rails in the running photo....odd. It is impresive that the engine is aparently under the sole in the 38. They give no figures for draft.

    All the best, Tad.
     
  5. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Doug Zurn is the designer of the Shelter Island 38, which I would contend anticipated the Picnic Boat in some ways. He worked for Chuck Paine before going on his own.

    See:
    http://thehamptons.com/main_street/runabout/lobsterboat.html
    http://www.turnstiles.org/articles/NewportBoat.html

    For Harry Schoell's 1980 patent 04193370 see:
    http://www.delphion.com/details?pn=US04193370__

    This patent, and subsequent ones modifying it, might also be of interest to you:
    http://www.delphion.com/details?pn=US05080032__
    The patent specifically applies to vessels over 200 feet, so you are free to design a yacht using this shape. I remind you that when scaling, say, a 700 footer to 35 feet the beam and freeboard should be scaled by the scale factor raised to the 2/3. In this example 0.05^(2/3) = 0.136
     
  6. gonzo
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    gonzo Senior Member

    I guess I was offering you sets of lines for a different kind of boats. If you are interested in the Hampton/Lobster boat type I can still send them to you.
     
  7. Tad
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    Tad Boat Designer

    Stephen

    I am not sure what you mean by "anticipated" but perhaps you should check your links. I first drew the Hinckley boat in 1993, one of your links has the Shelter Island boat debuting at the Newport show in 1996. The builder also mentions that they are chasing the Hinckley Picnic Boat market.

    When I first saw the Shelter Island I dismissed it as a copy. On further examination I realized it was in fact a very different boat. Though Joel/Zurn/Needham took part of the Hinckley concept, that of marrying traditional downeast styling with a modern bottom and propulsion, they had given it their own twist. They radically upped the performance envelope to 40+ knots, and included twin high-performance gas outdrives. As you may know the Hinckley boat is aimed at a high 20's cruising speed with a single diesel water jet.

    All the best, Tad.
     
  8. Willallison
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    Willallison Senior Member

    Gonzo - no I'm very interested in both styles! Anything you can send me would be enormously appreciated. Let me know any costs involved and I'll happily reimburse you.
    Thanks again.

    Tad - A PB38 (hull No.1, in fact) was recently bought by a local and I drive past the yacht club on a daily basis in anticipation of the day when it comes out to be antifouled. It does carry a spray rail a little above the rounded chine (is that an oxymoron....?)which seems fairly effective at keeping the boat dry. I've watched it underway - though at closer to 20 knots than 30 - and it slips along quite nicely. I suspect you are correct though - at higher speeds I would expect it might become rather 'damp'. The engine incidentally is under the sole.

    Stephen - thanks for the links - I'll check 'em out as soon as I get time. And thanks for the clues on scaling.....

    As an aside, one thing that has always irked me about hard chine hull types is the slopping noise the hull makes at anchor (my wifes a light sleeper - and if she's awake, then so am I! );) . I 'drew this hull with this in mind - it still needs a small keel and a few other bits and pieces, but you get the idea. Conventional shaft drive, cruise 18 - 22 knots....anyone have any thoughts?
     

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  9. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Responding to Tad:

    I'm not sure about the Hinckley vs. Shelter Island dates, and it might be interesting to check. It's my impression that the Shelter Island was early enough that it should be considered Doug's (and Billy Joel's) original thinking, not a copycat, but I don't know which was first. I thought it was the Shelter Island, but I may be mistaken. I think Zurn opened up shop in Marblehead just after I left (I'd been working for Jim Taylor) in 1992.

    On all other points I have no reason to doubt anything you've said, and would add that I like what I've seen of your work and that you're to be congatulated on your involvement with a very successful design in the Picnic Boat.
     
  10. Tad
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    Tad Boat Designer

    Will,

    I had a look at your hull, it's getting there. But, of course, I have some comments. I would not be happy with the kink in the sections from the after chine. I would get rid of the kink about station 5 and smooth the sections to a more natural shape forward. Make them (the sections) S shaped if you need that waterplane width.

    Your lowest waterline looks good. I would like to see the max width of the second waterline move aft a little and remain slightly fuller all the way aft. I would also like to see a more gradual sweep to the next waterline (close to DWL), instead of the hard turn at station 5 (midships). Smoothing the waterline will help fair the butts, which are a bit kinky for my taste, especially above DWL forward.

    Finally, is there enough volume below DWL to float the boat? It looks a bit shy to me. The most important part of designing any boat is guessing the weight before you draw the lines and then keeping track of weights as the design develops. Perhaps some numbers?

    Stephen

    Thanks for your comments, and sorry if I seem a bit defensive. Doug's site mentions opening his office in spring 93, by that time the Hinckley boat was drawn and two hulls had been tank tested at Webb. My references when working on the Hinckley were the traditional Bunker & Ellis picnic boats and a couple of Hunt designs, the Blackwatch and Little Harbor 36's.

    I did try to make the point above that the Center Harbor and the Hinckley Boat are two different animals.

    All the best. Tad
     
  11. gonzo
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    gonzo Senior Member

    I have lofted and built may Carolina boats. In my experience, when a hull has a lot of shape (flare) forward, a curved sheer makes looks hollow when seen from slightly above. We solved the problem by making the sheer straight on the forward section. Of course, because Carolina boats have a turn down sheer, it is easier to blend the straight section to a curve.
     
  12. gonzo
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    gonzo Senior Member

    These are pix of Carolina boats. I will send you some lines on Hampton boats next week. We just bought a house and are moving this weekend. Everything is in boxes and can't find anything:)
     

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  13. gonzo
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    gonzo Senior Member

    That didn't work. Let's see if they come out better.
     

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  14. Willallison
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    Willallison Senior Member

    Tad - 1st, thanks for the input.

    LWL 9m
    WL beam 2.7m
    Displ 4600kg
    LCB 57% wl
    AWP 18.9m^2

    Coefficients:
    waterplane 0.79
    Prismatic 0.71
    bloxk 0.40
    midsection 0.57
    D/L 177

    I assume you mean the lower 'soft' chine. My original intention was to to start with 's' shape sections at the bow which gradually hardened as they went aft, forming a quite sharp chine as it approached the stern. However, as I went along, this was the surface the computer modelled and I figured that it would probably be drier than my original idea - maybe not as soft riding though?

    I agree - a little work still needs to be done here. Essentially parallel waterlines are the go, I know, but I'm yet to figure out how they can be achieved when the fairbody sweeps up towards the transom particularly in a warped plane hull.
    Which brings about another question (I know - I got plenty!:D ) Below are two set of waterlines for this hull. The 1st represent the hull with level trim. The second with 3 degrees of trim - an approx running attitude - here the lines run closer to paralell.....
    Which should be considered for a vessel operating at semi-planing to planing speeds?
     

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  15. Willallison
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    Willallison Senior Member

    Oops - wrong pic - that was a rather poor render of the same boat....
     

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