As mentioned previously, precise templates are created for the ribs or bulk-heads required to build the hull. Those sections are then created in wood and placed in position on the keel. The keel itself is often built-up from several scarfed pieces, very much like the original.
A variety of grades and types of hard- and soft-woods are used, depending on the purpose, location and function. Wood grain often being an additional factor since the grain has to look somewhat natural at scale, but only when visible.
The sections are shaped and sanded to allow for planking to be applied in a smooth and fluent manner. Additionally cant frames and breast hooks are also often used in a model's construction. The picture above shows a complete set of master-bulkheads for a 19th century steam-sealer.
The clinker hull of a 3" 18th century ship's model boat shown below.
Hull construction of a modern Johnson 75 motor yacht model shown below.
After a yacht hull has been completely planked, she is sanded smooth and faired. Then the hull is coated with an epoxy-resin recipe, creating an incredibly strong, smooth and resilient hull.