Everything SHOULD be ok (other than nausea). The big problem is that if you do, G-d forbid, miscarry and you are bleeding and need a D&C, you need to make sure there is a hospital somewhere that can do that procedure.
When I was 9 weeks pregnant with my third pregnancy, I was supposed to go to Virginia on a golf trip with my husband and dad. My doctor said I could go only if I found a hospital within a 60 minute radius that could do a D&C b/c she was worried I'd bleed too heavily if I miscarried (I was on blood thinner). I called about 10 hospitals until I found one that did D&Cs. Couldn't believe it was so hard to find one. I wound up having bleeding while I was away, but it was very light. Ultimately, had to do a D&C back in NYC.
I think my doctor was very cautious only b/c of the fact that I was on blood thinner. Being on the boat will not harm the baby, so don't worry about that...