I'm sure my wife (the original poster of this thread) is thankful for your advice, but I should clarify things a bit. We had a shi-tzu for 14 years, who during boating season, spent her entire life onboard. She became very acclimated to boats, especially our tender - her taxi to shore. As a 7 week puppy, we did crate-train her at home over the first winter season, successfully conditioning her for extended offshore passages.
However, we are now faced with the prospect of training our next dog during boating season. We are concerned about how effective "crate-training" is in this environment.
BTW, our boat displaces 18,000 lbs and I don't think an 18 lb dog would make much difference. Also, please tell me the name of a pet store, that house-trains a puppy before owner adoption.