While my cockpit is much more complicated than the stock design
Gig Harbor Boat Works sliding seat),
Here's my process:
- Acquire an oversized piece of cardboard.
- "Rough" cut it to be within a couple inches of all four "sides."
- Line up the straight edge of the seat front with the long straight edge of the cardboard, and fasten the cardboard down so it cannot change position at all.
- Cut ten to fifteen 2-inch wide strips of cardboard that are four to six inches long.
- Distribute them evenly along the transom, hull, and bulkhead edges of the cardboard.
- For each small piece, slide a narrow end so that it touches a part of the boat, and tape it in place on the big cardboard sheet.
- After fastening all the pieces down, remove the cardboard and place it on your sheet of plywood, again aligning the long straight edges (and securely fastening them together).
- Mark the plywood at each of the small ends.
- For the hull curve portion, pound in nails at the marks to hold a batten against so you can draw the curve.
- A straight edge should be sufficient for drawing the lines at the transom and bulkhead ends.
- Remove the nails after drawing your lines, and cut out the piece.
- Test fit the plywood and trim as needed. (And be thankful for "the gap-filling properties of epoxy.")
- (In case your build has some asymmetrical qualities to it) Remove the two-inch strips from the large sheet of cardboard, flip the sheet over and place it on the opposite side of the cockpit. Repeat the above process.
For creating templates for other parts I tweaked the list as follows:
- Replace items 1. - 3. above with: Cut a piece of cardboard into a SIMPLE geometric shape that nearly fits within the space you need to make a part for.
- 4. Cut plenty of small strips that are big enough to tape to your central piece of cardboard and to reach the edges of your build.
- 13. Might, or might not, apply to the part you are making.