Originally Posted by Terra Nova
Why ask why? The boat's manufacturer tells you it is unsafe to mount a motor
with more than 10 hp. Period.
Is it unsafe? Come to the Bahamas
and see what they do. You seldom have too much power when you're cruising as your dink is your workhorse, often heavily loaded.
Here's a post from a CG petty officer:
Re: Max hp and small boats
This is the Coast Guard formula for determining max hp for boats under 20' in length. Note that when determining max hp, the manufacturer is apparently free to state a lower rating if desired, and sometimes does.
(2 X L X W) -90 = rated horsepower
W=transom width; if the boat does not have a full transom,
the transom width is the broadest beam in the
aftermost quarter length of the boat.
The rated horsepower may be rounded up to the nearest "5".
The above is simplified from here:
And remember, it is not a violation of Coast Guard regulations
to install or use an engine
larger than specified on the capacity label, but there may be state regulations
prohibiting it, and restrictions from your own insurance
company regarding this.
There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded.