I'm not so sure I'd use a Dumas motor. What they have sold in the past(notice the past tense) have been old tech and not the newer and more efficient ones.
I'd personally check with Mack R/C Products. They sell boat kits, hardware and running gear for models. This would be for a more scale boat.
If you want more of a race boat, I'd contact Offshore Electronics.
The links to both are listed below:
index
https://www.offshoreelectrics.com