Boating operating under the influence is just as dangerous and every bit as illegal as operating a motor vehicle under the influence. The legal limit for both is .08%. Penalties are also similar.
Here is the difference. There is not usually education required to operate a boat the way there is to operate a motor vehicle. An educated boater is 70% less likely to be involved in an accident, however.
Every year in Arizona alcohol is directly related to fatal boating accidents. 50% of all fatal Arizona boating accidents were alcohol related in 2007 and 1/3 of all fatal boating accidents nationwide are alcohol related.