If you're in the NYC area, may I suggest a cruise up the Hudson River? It is not only spectacularly beautiful, but the transition from salt water to fresh water will kill all that stuff on your bottom and give you a free bottom cleaning.  The salt/fresh boundary is guaranteed to happen somewhere south of Poughkeepsie so be sure to cruise at least that far north and stay a day or two to kill those critters.

Kingston, NY and Saugertiese NY are two great cruising stops along the Hudson.

I'm not in the NY area - I've used Trinidad SR here in the SF bay area - seems to work as required.

As I recall on a W32 - one coat on an existing Trinidad SR bottom -- cleaned  and rough sanded - took about 1.25 gallons - all depends on how thick it is applied.  My second coat always seems to need less material - though - maybe I was to tired to apply as thick as the first coat... I use a roller to apply.  

Spraying is smoother (usually) and I would guess a thinner coat - though of course you could apply more coats to get the same total thickness. 

Another idea is to change the color of each coat of the bottom coat so you can tell how well you are covering -- and later you can see where it is wearing out... 

Hope this helps.

Jay

Thanks for all the responses.