View Full Version : Just what the world needs, another ply pram!
02-09-2004, 09:19 PM
Here's what's been on my board lately, yet another plywood pram: Y.A.P.P.
7'10" X 47"
Still a lot to be done. I haven't really worked out the rig and foil placements and sizes. Also need to work out the innards.
But the general shape pleases me. I've also got this boat stretched out to 11', but no rig for it yet.
Trying to decrease my bilge ratio. ;) :D
02-09-2004, 09:32 PM
Clever- should be fast, if a bit tippy. Lots of trade-offs to consider, eh? I looked at hundreds it seems before deciding on the 11' Arch Davis skiff (Sand Dollar). The flat bottom/narrow beam is one compromise for speed/stability, and sailing it will need to roll up on a chine to go fast. Yours should be a quicker all around boat, but maybe not as kid friendly? Nice work! smile.gif
02-09-2004, 09:39 PM
John, would you be willing to tell some of us who know nothing about the details of designing a boat how you go about doing that?
Were you trained in a school? Learned on your own?. Mentored? Use a CAD program? Use some standard reference books for sail size and design?
It would be interesting to know how these boats that I sail come from a dream in ones head to a plan on paper.
02-09-2004, 10:40 PM
Oh, I ain't learned nothing yet. I just draw what looks good to me with the tools I have at my disposal.
I base most of my designs by thinking about an exisiting design that I'm familiar with and take the general proportions and construction details to get me started. The boat above got its inspiration from Bolger's NYMPH and the Merten's D4. I'm not breaking any new ground, that's for sure.
I generally sketch out the general layout and proportions on paper. Then I work out the hull using Gregg Carlson's excellent Hulls program (free DL at http://www.carlsondesign.com ). Hulls gives some rather rudimentary hydrostatics which helps me try to make a semi-educated guess about whether or not it will float like I want it to, whether or not it will be too tippy, and whether or not it will carry enough of a load to be useful for my intended purpose.
I then export the DXF files of the hull, the expanded panels, and any frames or bulkheads generated by Hulls to a CAD program. There I smooth out the crude drawings by a time consuming and highly inefficient process. Usually, I'll build a poster board model of the hull at this point to confirm that it looks OK in 3-D and to do some static float tests. It's not unusual to for me to go through several iterations at this point to tweak it a bit to fit my aesthetic sense. My kids usually destroy the models playing with them, but there is still a stack of them sitting on my desk as I write this.
Usually I'll print out the hull and rough out thedetails with pencil and paper. Then back to CAD to laboriously draw them that way. I figure out balance with the seat of my pants and a few rules of thumb. That's the area I'm least comfortable with. The one sailboat I designed that got built apparently was OK in that department, so I'm hoping I stay lucky.
Somewhere in this process I'll work out the nesting of the various parts onto plywood panels. I've been known to go back to reshape the hull slightly to get a more efficient use of plywood. It's amazing how that kind of stuff sneaks up on you. I can't imagine doing it without computers, either. I once worked out by brute force how to expand panels (on a Naples Sabot), but I never trusted the results.
I've read a lot of stuff, took some notes on some, studied a lot of plans from guys who know what they're doing (Bolger in particular), let others critique my work, and generally tried to draw what looks good on the assumption that if it looks good, it is good. But it's mostly for fun.
The boat above has been on the board for a while now, and I already see things I want to change. Really, the 11 footer is what has my attention. I've also got a 16' outboard Garvey to the point it could be built waiting for the day I have the time and money to build it.
[ 02-09-2004, 11:04 PM: Message edited by: John Bell ]
02-10-2004, 12:42 AM
One time I tried to explain to a friend that remodeling her bathroom was no big deal. I'd just rip everything out, tile the floor, put in some greenboard, paint it, replace the stool and shower and BING new bath.
She looked at me like I was a wizard.
I'm looking at you like you are a wizard. smile.gif
I could never do what you do. But I'm glad there are guys like you that do know what to do. smile.gif
Thanks for the explanation.
02-10-2004, 10:38 AM
Originally posted by John Bell:
Trying to decrease my bilge ratio. ;) :D You're doin' good. Why there is even hope for alteran.
02-10-2004, 11:09 AM
Al: Like anything else, there ain't no wizardry. If you look at the finished whole of anything, be it remodeling a bathroom, designing or building a boat, it will overwhelm you to where you won't ever begin. Instead, I think about it as a bunch of little steps that I have to figure out as I go along. Do the first thing, then the next, and the next, and so on until one day there aren't any more steps and you're done. Along the way you'll learn some lessons and the next time you do something those lessons will help you do a better job.
I'm no pro (that's obvious!), and I've certainly oversimplified my assumptions when I draw something. I read things like Tad Roberts' recent series on sailboat design and performance in WB and realize how little I actually know or understand. However, since I'm not building something, the act of designing takes the edge off that particular urge.
Struggling to write it down keeps me aware of how little I know. But that's why boats are so endlessly intriguing, there's always more to learn. As long as you think this boat will be better than the last one, life is good.
Take care, Tad
John, I was thinking about your design in work today. There is a modification on the Cape Cod Frosties that I think you could use, it's easier to do than describe: It's at the transom and tends towards making tumblehome or at least cutting down on the wedge effect that happens at the deck, transom/sides interface. It's basically a horizontal sawcut about a foot or longer, maybe 4" below the deck on each side of the boat, cut an extra angle on the transom (mirrored on the other side). I hesitate to call it a chine, but it's an extra little stitch and glue seam that you slide in there. People who sew would call it a "dart". Tom Leach was the brain behind the Frosty, so I'll give him credit until the right guy comes along.You gain something that's nice aesthetically, practical because it reduces a large dimension that does not need to be large, especially useful if you are tacking close to moored boats or sailing away from a dock (you know how that back corner of the boat always catches). Slides into a station wagon easier too.
Pete Follansbee who lives in NH and is quite a builder managed to torture the ply enough in his Frosty, to have a round bottomed boat at the transom, if I remember there was still a bit of a chine, but he eliminated the "dart" and had the sides rounded or the same effect, can't say whether it was any faster because all Pete's boats are fast.
[ 02-11-2004, 08:35 PM: Message edited by: Hwyl ]
02-11-2004, 09:03 PM
Delightful boat, John! But don't you think a few cubic meters of water ballast would help settle her down? ;)
As for "taking the edge off," I've had exactly the same thought. I'm not building this summer, so maybe I'll play around with another design. I just ordered Larsson/Eliasson.
02-23-2004, 11:59 PM
Looking at Gartside's little 12'er in #177 got me back to work on the 11'er I mentioned a few posts up in this thread.
This one is 11' x 58", ~71 sq ft. of sail. This is the first boat I've drawn with a pivoting centerboard. To get her down to the 5" WL will take ~500 lbs. Still much to do, but I think this is a much more practical idea than the 8'er above.
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