Why does alcohol tend to have a greater effect on a boat driver than on a car driver at the same BAC?

1. Alcohol has no different effect on the water compared to on land
2. Waves, motion, vibration, engine noise, weather, wind and spray can all multiply the effects of alcohol on the water
3. Boats always travel slower than cars, so alcohol's effects don't matter
4. Boat licences do not require any coordination or judgement