Lately there has been a few places on the net, and on this site as well about laying out using a ticking stick. This is a tried and true method and requires very little in tools, or materials, but is slow and has room for mistakes. I was watching a clever young shipwright fit up some very awkward bulkheads a few years ago, and although I have been a journyman fabricator for nearly 30 years I had never seen it done his way before. After, it seemed so simple and obvious.
His tools consisted of (1) a bundle of strips of “door skin” which is that cheap “mahogany” plywood that is about 1/8 to 5/32 inch thick, often sold as “cabin grade” ripped into 1 inch wide strips. (2) a hot melt glue gun and glue sticks, (3) a pair of tin snips or sharp utility knife, and (4) a staple gun and roll of masking tape for vertical and overhead work.
The technique is to place a strip of the plywood , trimmed to length along the longest straight side and tape or lightly staple it in place. Then, place another trimmed strip along the next side and hot melt glue the corner together lapping one over the other at the corner. Proceed around the perimeter the same way, overlaping and hot melt gluing each corner or change in direction. When you come to a curve or any fit up that is not straight, which will be most of the things you encounter on a boat, simply place straight pieces touching only at their ends, (chords, remember middle school geometry? ) and using many shorter pieces trimmed to a point, glue them radially onto the chord as close together as necessary to follow the curved perimeter. If you are working on the flat such as a new sole or a cockpit grating there is no need to tape or staple the pieces down while you work, although if you are clumbsy like me, taping might be a good idea to prevent you from knocking the whole works out of kilter when you jump because you burned yourself yet again on the glue gun. (dang, those things get hot, and that glue just sticks to you till you blister than tears the blister off when you try to pull the glue blob off.) Maybe a thin pair of gloves would be in order.
When you have gone all the way around the perimeter it is a good idea to put a few diagonal braces across the corners and if it is large, maybe an X brace to keep everything from going out of square when you move it around. If there is a taper to the hull or adjoining pieces, and there probably will be, take into account that pieces of 1/8 ” material lapped one on the other will be 1/4″ or more above the actual point of contact and if the taper is 30 degrees that will amount to over 5/32″ too large or too small. It works best, when plotting curves to have your radial pieces under your chords, in contact with the point on the hull etc. that you are trying to fit to. If you have an existing piece and you are trying to duplicate it without removing it it is easy to tape or staple the strips flat to the face, but if you have nothing and you are trying to make a pece to fit in the hole it is sometimes easier to prop a piece of carboard or thin scrap plywood to act as a guide for your template or maybe even as part of it, gluing your strips to the pannel as you go.
When everything is cool,(this is important, as the glue remains quite plastic till cool) peel away any tape, or remove any staples and carefully remove the completed template. At this point you are going to find out if in fact the piece you are hoping to make can in fact pass through the openings in the hull you have available. This is one part of this technique that no other method can tell you. If the template doesn’t come out, you can be assured that the new piece will not go in. Any way, once you have it free, simply place it the correct way out on your plywood or whatever, orienting the grain to best effect and, holding it down with a few small clamps or wieghts, trace it carefully and cut the new piece out.
You can even use this method in a 3 dimensional way to make wierd and unusual tanks and such to fit all those odd unused spaces, knowing that if you can get the template out, means you can get the new piece in, and for that space under a lazarette or Vee-birth where there are no square corners I’m unaware of a method which would work better.
Give it a shot, it is a very satisfying thing to drop a cabin sole into place and have it fit PERFECTLY the first time.