DO NOT DO IT.
I actually know a girl who went on a speed boat while pregnant. Unsure of whether or not she actually got on the tube, but other people on the boat were. She had been wanting a baby SO bad, and had finally gotten pregnant.. She miscarried because of doing that. My sister was there with her, and also pregnant. They asked her to go, but she refused to get on, and tried to warn her friend.
I also want to point out, you don't even have to fall out/off to hurt your baby! Those bumps alone can cause you to miscarry.
As far as fourwheeling. I did once, but I warned my guy we weren't going over any bumps, just rode down the street. It still scared me to death, because after we got a little ways I just kept visualizing us crashing and my stomach getting impaled. Wouldn't do it again, even if we went slow & there were no bumps.
Now a SAILboat, not a speedboat, should be fine in good whether with competent driver
at 8:14 PM on Jun. 6, 2010