I have used Oversea Yacht Insurance in San Diego as my insurance broker for years......They are legitimate in my opinion and shop each year for the best insurance to fit my needs and the boat....I have had good luck with them for over 30 yrs.....
This year they recommended American Modern...I had never heard of them, knew nothing about the company.....I was assured by Oversea that they have been around for a long time and they use them routinely...This year they came in with a substantially better quote than the others for the same coverage.......
I did some research and was satisfied that it was fine....
The true test of course is claim time, which I have not had to do ...