The hunting regulations cover shooting from a boat or blind in numerous areas. The statute listed above for weapons in a vehicle does include vessel in the text, but the intent of the statute is directed more at non-hunting activities and would be more applicable to someone waterskiing with a loaded shotgun/rifle, etc.

Waterfowl hunting (with the proper permits/licenses) conducted in accordance with state regulations is a permitted activity. Obviously if someone had a boat going full speed acting like an anti-aircraft platform shooting at everything in the sky there may be an issue, but a boat anchored or even drifting with the current/tide is not under power and could be considered a blind (or if anchored a stationary blind).

It would have been much cleaner if the statute specifically listed waterfowl hunters as an exemption.

Safest thing to do, and just about every waterfowl hunter that I've ever run into does it this way, is to unload and put the shotgun back in the case when the boat is under power. It's a good common sense/safety position to take so you don't have any accidental discharges in the boat when it hits a wave or when you try to pull the shotgun out of the case.