Amateur Design Question

[Shalfleet]

I am almost ready to plank my first boat, (Sand Dollar, designed by Arch Davis) and I am planning my next boat which I hope to design myself.

I have started to read a couple of books on boat design and would like to build a 14-15 foot day sailer with classic lines, a slight hollow bow, overhangs and a small curved transom, perhaps with a slight wineglass shape. I would also like to 1/2 deck her.

The building technique that Arch Davis recommends with ply planking on stringers seems very logical, light & strong and I intend to use this approach on my next boat.

Does anyone foresee major problems with building the type of boat I describe using this approach?

I know I have a lot to learn, and I intend to seek professional advice and build a model before taking the plunge, but a thought I would ask a few initial questions first....

Thanks!

[Ian McColgin]

For the shape you're describing, ply seems a bit inefficient. Since you appear to like mod methods, maybe think of a stripper.

As to designing her yourself. I'm personally way too lazy to build something I'm not very sure of so even though I fancy myself pretty smart about hull shapes, water, wind, and all that, I'd be loath to design wholly new. Maybe streatch a nice shape a few percent but not much more.

Take a really simple shape - LFH has a simple looking dink for the MarcoPolo and I had a chance to row one properly made and row a similar sized boat of just slightly different shape. It's not for nothing that LFH is understood to be a genius. Amazing what apparantly trivial changes can do to wreck a good model.

And that's a simple shape where anything will work a little. In fact, before trying the LFH model I'd spent a life time rowing most anything and did not realize that a hard chined little pram could be such a zippy boat - most of them just don't make it.

It's really hard to harmonize your shape with the medium - model up a nice looking bow and discover that the planks just won't run - that kind of problem. If you don't already see this, then no way are you ready to design your own. And even if you do . . .

I'd pick a good design to fully understand and execute, especially since you're looking to a pretty sophisticated shape.

Or, what the hay, buy and restore an old Thistle and understand why she's so hot.

G'luck

[TomRobb]

The description sounds a bit like a 12 1/2.
Ply doesn't do hollow bows well.

[Paul Jeffrey]

I would have to agree that ply would not be the best material choice for the hull planking. Strip plank would be the better choice for this type of hull shape as you discribe it. Strip plank lends it's self very nicely to many hull shapes.

You have two options in planking, one is to use say 1/4" thick planks and then apply two layers of 1/8" veneer over it in a cold mold method or two to go with planks that are 3/8" to 1/2" and the apply two layers of 6 oz glass cloth over it or 12 oz uni-directional glass across the planks. Either will give you a strong hull.

As to designing your own boat, I'd say go for it. Do your research on hull shapes you are interested in. If you can go look at as many boats on the hard as you can that are in your area. Visuals are always good. Do a scale model of the hull after you design the hull. Mark the water line and ballast the boat to the line. You can do some super cheapo tank testing in a swimming pool or even one of those reflecting pools in plaza's in bigger cities or even a mall. Granted the malls don't like you doing that but all they can do is kick you and the model out.

If you draw up the lines by hand you can then take the offsets and input them into a free design program like Hullform 7s they have a free one available on their web site. It's by Blue Peter Marine in Oz. That will give you the ability to see the hull 3-D plus get the calc's on it. You can then save the file of the design download one of their demos of their latest program and open it there and do hull shading and look at the boat in VRML on the screen.

What ever you do understand you will more than likely design more than one hull in the process. But designing and then building your own boat is a real kick. Have fun.

[ 04-22-2002, 11:28 AM: Message edited by: Paul Jeffrey ]

[Don Maurer]

Iain Oughtred's Tammie Norrie has a hollowed forefoot. I used the stringer method, but found the strakes did not follow the stringers well between station 1 and the stem. I'd suggest if you go this route, that you space your station moulds fairly closely in the hollow area. You may also want to build the stringers in that area of laminated 1/4" strips.

[Shalfleet]

Many thanks for the advice so far, greatly appreciated! I have downloaded the Hullform software and it looks like is will save me a lot of maths, plus increase accuracy a bundle (Thanks Paul!). I think I'll stay clear of strip/multi layer construction as I believe this will require a lot more epoxy than I really want to work with, although it would give more flexibility in hull shape. I'll sacrifice the hollow bow if need be but further study of Tammie Norrie might help my cause - Don, do you have any pictures of your build?

[Don Maurer]

I'll see if I can find some photos that show the forefoot planking. It may take a few days to locate them and get them scanned in and posted.

Don M