A homeowners policy treats a boat as a side item. It gives some property and liability protection, but with tight limits that leave a valuable boat badly exposed. The examples here follow the 2011 ISO HO-3 as described in a public trade article; other forms and insurers vary.
Property gaps:
Watercraft, together with their trailers, equipment and outboard motors, fall under a low dollar sublimit. A covered peril such as fire does not lift the sublimit.
Theft of watercraft is covered only on the residence premises, so a boat stolen from a marina is not covered at all. A sublimit caps a covered loss; it cannot create coverage where the peril is restricted.
Windstorm damage to watercraft is covered only while the boat is inside a fully enclosed building.
Liability gaps (Section II of the 2011 HO-3, assuming no racing, rental, carrying people for a charge or business use):
An owned outboard boat of 25 hp or less keeps liability coverage.
An owned sailboat must be under 26 feet.
Owned inboard boats are excluded.
A larger outboard owned before the policy period is covered only if declared at inception or reported in writing within 45 days of acquisition.
The fix is a boat owners policy, or a yacht policy for larger vessels, which follows the boat wherever it is and is built around boating losses. A watercraft endorsement on the homeowners policy (see the Insurance on Residence chapter) adds liability only, not coverage for the boat itself.