I went through this same problem many years ago. You need two primary policies and one umbrella policy (if you are worth enough to worry about it).
One primary policy is auto renter's insurance. All of the auto insurers know how to write this policy. It is for people who don't own cars but rent them as you will probably do while you cruise
. The insurance supplied by car rental companies has pathetic liability limits, typically $25,000. You probably need $250,000/500,000.
The other primary policy is like homeowners and it is a personal liablity policy. State Farm for one, writes those policies.
And finally if you need it, take out a $1 million or so umbrella policy that picks up where the other primary policies leave off. Make sure that it applies to your boat liability as well.
The whole thing costs about $1,000 per year.