Rare that I disagree with Rick, but have to here. Like the yard's subcontractor, you have no direct claim against the yard's carrier nor are you bound by any exclusions that policy may contain. We have not seen the contract, if any, that you signed with the yard, and those things vary from nothing, a scrap of paper to an indecipherable 10 page tome. That said, most judges are trying to figure out what you thought you paid for, and what reasonable expectations you had a right to regarding the work. When dealing with the public, a yard that contracts to paint your boat and ends up punching a hole in the hull is hardly going to get away with pointing the judge to a clause saying neither they nor their subs are responsible for "professional negligence" any more than will a used car dealer who misrepresents the condition of a car and then points to the "as is" clause. Assuming the screw up is demonstrable and you can prove they or their subs did it, the real battle will be between them. You should get what your bargained for or the money necessary to accomplish it.
It is indeed true, as Rick says, that all our policies, auto home and boat, require us to report losses promptly. However, the company can generally only avoid liability if they can show the delay somehow prejudiced their ability to mitigate their payout. Insurance companies are largely disinterested in your claims; just your premiums.