What Kind of Contact?
To ask questions about the boat the broker might not know?To buy directly from the owner, bypassing the broker?The question is so vague as to be difficult to respond to coherently.If the boat has a "For Sale" sign on it with, or you see an ad with, the owner's contact info., the owner is downright inviting you to call him. If the only info. is the broker, then the broker is representing the owner.Asking the broker for the owner's number when it is not offered elsewhere I believe is a bit gauche. The broker can forward any questions/requests for information to the owner (again, he is the owner's agent in any sale). That's why has engaged a broker in the first place: to earn a commission by exposing his boat to a large body of potential buyers, and to handle details the buyer doesn't want to bother with; in essence, to keep his phone quiet. The suspicion that you will try to talk the owner into bypassing the broker in a direct sale-by-owner might arise.Nothing illegal about that (taking Steve's comments about the seller's contract with the broker in to consideration), but you asked about appropriateness, and appropriateness is a matter of etiquette, not law.