Parts look great! Keep printing!
I have a wooden boat appr. 1 meter long with 2 paralel motors (brushed) and they generate a lot of heat...but with the wooden hull it is not a big problem.
PLA may melt and bend, I would either go with water cooling or at least with ALU heat sink. Sorry, I do not want to sound Mr. Know-it-all but losing the motor while riding the boat b/c of a melt hole in the bottom of the hull would not make you happy I guess....:-)