Try a boat specialized company like Pantaenius
American Yacht Insurance
That's an international company based on Monaco. I have been insured by them and I thought they had the best prices and coverage till someone make me an offer on behalf of Groupama (the ones from the French boat on the VOR) and I could not believe on that offer
But they have insurance only on Europe even if my boat will have a world wide insurance, for less than a limited insurance from Pantaenius
.
Regards
Paulo