Some homeowners policies cover boats, some auto policies cover trailers or boat and trailer while in tow. Both having loopholes or exceptions. A policy specific to a boat obviously best. Ours (US) being such a litegious society, when you mention racing it can, in some cases (carriers/agents) open up even more "black holes".
We are only discussing boat coverage. Want to get some different views of "what is required", start talking about insurance for clubs/fleets and hosting regattas, and who is covered and not!