Hi Dave - insurance is still kind of hit and miss when applied to boat sharing arraignments - surprisingly, it is still new enough that agencies are tentative with it. I'm currently using travelers (Texas) and also got a little bump last year. My policy is basically the same as if I didn't have a partner, but I'm including my partners as additional insured on the policy - just like you would a spouse or a neighbor who uses your boat often.
No magic pill here though - insurance for boat sharing arraignments is still kind of on the bleeding edge for the very slow to move insurance world. Just keep calling around and eventually you'll get the right policy.