I’ll take a random guess that a 30kg boat at 1-2m/s requires about 250watts. 30kg is probably a little smaller than mine which has a 1Kw motor and a top speed of about 3.2m/s. The speed vs power curve is completely non-linear though so even a small increase in speed can require a massive increase in power.
I put a speed vs power graph for my boat on this blog post.
Another random tidbit I learned during my recent project is that a longer boat has a higher top speed because of the effect of the bow wave.