All vessels are defined by their shape which means these curves do make awkward spaces to make structures to fit, for example bulkheads. It is necessary to make a bulkhead which fits perfectly against the hull for structural integrity, water tightness etc.
Usually this process is not easy, and happens in a confined space with other structures about you. The hull side may not be a uniform curve or have beam shelves for the bulkhead to be fitted to. So it is a complex shape with limited space and a high degree of accuracy is required.
There are two common ways to achieve this; firstly, using patterning sticks and a glue gun to make a physical pattern ,and secondly using a flag and a spile stick to capture this shape. Chris Rees will show the second method on a bulkhead in Grayhound.
The process is demonstrated in the accompanying video clips with a step-by-step guide. The conversation with the boat builder, in this case, Chris Rees is unscripted and covers the technique from his experience.
Take the pattern material ('the flag') and fix it next to the section which requires capturing (use screws, nails or a clamp). The flag does not have to be shaped, it just needs to fit in the space in a suitable way.
Decide on the points which need to be recorded to recreate the required shape; if it is a complicated shape, increase the number of points recorded, especially on a curve. On a straight line, you only need the start and finished point to recreate it whilst for a curve you may want five or six points.
Using the spiling stick (mark one face as top), lay the stick on the flag with the tip touching the point. Once happy draw along the stick (the side with the notch) and around the end. It is important to label each point. Then repeat for all of the rest. If a camera is available, it is worth taking a picture of the flag in situ just in case there are issues later and the photograph will help to unpick those.
Remove the pattern, and place on the stock to be used for the bulkhead, and secure it again. Lay back the stick carefully on each outline and once happy with the position a cross can be marked at the tip of the stick. Again label each point as it is drawn.
After all the points have been transferred to the stock, they can be joined up with a ruler or if curved with a suitable batten to recreate the shape.
This approach to pattern making is low tech, but it works and has passed the test of time.