Doesn't "Coastwise" pertain to moving
commercial cargo with maritime traffic?
You should check out the simplified procedures for small vessels at the NVDC website. I think all you need to do is to complete the CG-1258, a copy of the title or
registration, and bill of
sale.
But to answer your question directly, from the FAQ portion of the NVDC website:
"WHY AND HOW IS BUILD EVIDENCE ESTABLISHED? Evidence that a vessel was built in the U.S. is required for a vessel which is to be used in the fisheries or coastwise
trade. Build evidence is normally established by submitting a Builder's
Certification on form CG-1261. That form must be completed by the person who constructed or oversaw the construction of the vessel or an official of the company that built the vessel who has examined the records of the company to determine the facts of build."