Guys,
I purchased several of the ESCs referenced by HARQUEBUS above. I haven't tried them in a boat as yet, but I did hook them up to a battery, motor, and receiver and they seemed to work nicely. There is a decent dead band around the point where you want the motor to be off so it should be easy to control the boat when "docking". They are very small and light and the price was right as well.
Bob