Rick,
Your question seems to be a frequently asked one. Google "Open Container Laws Boating." The consensus seems that having an open container is not illegal. The consensus is that the operator of the vessel can not be impaired and those laws parallel motor vehicle laws, i.e., .08% BAC.
NY has recently tied BUI and DUI laws closer together. In the past a BUI didn't count towards future DUI penalties and vice versa, now they do. On a subsequent conviction on either a DUI or BUI prior BUIs and DUIs count equally towards increased penalties.
One little known USCG regulation is that the Helmsperson may not be considered the operator of the vessel. The operator is Captain, on commercial boats, on recreational boats it is the owner or the person who normally commands the vessel. Joe Hazelwood (Exxon Valdez Captain) learned this the hard way. Locally, a few years back there was a boating accident in Oswego NY, while the person driving the boat was not impaired, the operator/owner was. He was arrested for BUI.
Banning open containers on recreational boats presents challenges that are not present with banning them in motor vehicles. Larger boats will often have open bottles of liquor stored in the cabin. It would not be practical to ban all open containers, especially in larger boats.