How to figure hull plywood hull panels

[jtrieck]

The boat I want to build is odd. It's simple, but odd. It is double-ended with a single 'midship mold. The top is completely decked and the freeboard will be approximately 6" and the sheer will have maybe 3" of upswing at the ends. It will be sort of like a 6 hour canoe, except shorter and with more beam, and obviously much less height.

My question for y'all: Is there a simple way to figure what the expanded shape of the sides will be? I can provide more specifics if needed, just tell me what you need!

JTSR

[TerryLL]

My question for y'all: Is there a simple way to figure what the expanded shape of the sides will be? I can provide more specifics if needed, just tell me what you need!

JTSR

I'm aware of two simple techniques.

1. Loft the boat to scale, say one quarter. Frame the model. Make a pattern of the panel from the framed model. Scale the pattern to full size. What could be easier?

2. Well, this: Plug your offsets into a CAD program and click RUN.

In either case you'll need a set of offsets. For that, you'll need a set of lines in three dimensions.

[S B]

The "other "simple method is; attach plywood to boat and cut off everything you don't need.

[ShagRock]

As Terry alludes to, it would be easy to conceptualize if you gave your expected length, beam, and depth.

Sounds similar to the method linked below for a tortured plywood canoe.

http://www.sloejd-kbh.dk/tema/skibe/Kano_GB/Canoe.html/htm

[Spokaloo]

Check out how Redmond did Whisp as well. Lapped panels together before construction means they just wrap around the panels and you are floating in no-time.

E

[pandelume]

Depending on exactly what you're looking to do there are several pieces of software that might help. The plan of attack will probably depend on 1) boat characteristics (i.e. number of strakes or panels, amount of twist per panel, etc.) and 2) how comfortable you are with computers/CAD vs. hand calculations or just trimming the panels on the jig.

Is there any chance you could post a sketch of the design? or maybe a picture of a similar boat? As a starter you might try the Carlson chine hull designer.

[paladin]

Make a model from stiff posterboard with an inch and one half grid on it, tack it together to get the shape that you want, open the pieces up, carefully measure everything, then multiply times 8 for the real size....

[S B]

Take thin piece of board as long as the boat, plywood is good it won't edgeset, draw a line down the center of it. Attach the board to the side of the boat, roughly in the middle.With a compass, triangulate all necessary measurements,from the boat, to the line. Remove board to flat surface and reverse procedure to establish shape of panel.

[Don Maurer]

If the chine is parallel with the sheer, the shape is simple. It is a trapezoid. Check out Jim Michalak's tutorial on boat design http://marina.fortunecity.com/breakwater/274/2005/0115/index.htm#Drawing%20Boats%202

[dguidry]

Secure a cheap piece of plywood approximating the shape of the final piece, to the frames and mark semicircles onto the piece with a compass from all critical points on the frames, chine, etc. Remove the plywood piece and lay it flat on the actual plywood from which you intend to cut the final piece, and reverse the process by placing the compass point on the arc of the template piece and draw a semicircle on the final piece. Do this again from another point on the same semi-circle of template piece. What you will end up with is a "x" where the two arcs meat. That is the exact point on the new piece corresponding to the reference point on the frame or chine, etc. Once you have marked all these points, extrapolate between the points with straight edge where appropriate or fare as warranted. This sounds complicated but its the most precise and quickest way to do it. Good luck.

[boylesboats]

Spile it........

Take a strip of flexible batten or plywood about 4" wide and longer than the boat you're building.. tack on several cross pieces every foot.. like a ladder..
Lay it over the forms, those cross pieces should be long enough to reach from bilge to sheer, mark off where it contacted the surfaces, then transfer those marks onto the panel.. connect those tranferred marks with another batten, draw it out with pencil then cut it.. Easier done than said here..

[pandelume]

Not sure where you went, jtrieck, but spiling (per boylesboats and others) is the traditional method, and from what I can tell isn't that difficult.

Spiling is done as part of the assembly process, however. If you want the panel shapes before building anything, making a model - either a physical model or a CAD model - is probably the way to go. I'd say Paladin's suggestion is the most straightforward for a hard-chine skiff. I asked before, but is there any chance you could post a picture or a link to the design?

[Cuyahoga Chuck]

What you want is a flat panel projection. Today it's usually done using a special computer design program like Rhino. Then there is the old way. Build a stick framework and take your panel shapes off that. Then there is the easy way. Spend $35 for the plans for this
http://www.bateau.com/studyplans/D12_study.htm?prod=D12
12 ft. long, 44 in. wide double ender, suitable for oar or sail.
The reason I threw in the last suggestion is because you mentioned the Six-Hour Canoe.
It's claim to fame is that the creaters got someone to publish a book about the construction. As a paddle boat it is an abysmal design. The two guys who did that hull didn't have a grip on what makes a canoe handle properly. In fact, they may not have been intertested in that. They were a couple of college professers who had come up with a social uplift program and the canoe was the centerpiece. They drew the chine line on the side panels straight and got a boat with way too much keel rocker and upjutting stems that will allow the boat to spin like a top in any kind of cross wind.
Unless you have a fair idea of what is required to make a boat handle properly you are liable to produce a box that floats with no discernable virtues.
As simple as the D12 is it was produced by a naval architect using a computer design program and a lot of accumulated experience to massage the hull into something that is passable both at rowing and sailing.
Another possibility. Download the free plans for the Cheap Canoe.
http://www.bateau.com/freeplans.php
Make two of the side panels, spread them as far as you like and put a bottom on it. At least you will be in the ball park.
Good luck.

[Clip]

I did an on-boat panel measuring project when I widened the hull of a whaler.
It is somewhat described in my Blog at:
http://www.backyardboatbuilding.org.uk/forums/blog.php?b=14
It did work fairly well, though fine adjustments did require the upper panels to be allowed more slack, since plywood did not fully like being bent as much in two dimensions.

[boylesboats]

Another possibility. Download the free plans for the Cheap Canoe.
http://www.bateau.com/freeplans.php
Make two of the side panels, spread them as far as you like and put a bottom on it. At least you will be in the ball park.
Good luck.

I just played with that idea..
If ya deepen the sides to 20" and spread them apart about 30" at the center of chine and 54" beam at the sheer, ya got yerself a double ended dory, a gunning dory that is...