On Chill Ouat we use a 5 hp short shaft merc.
We find that it pushes the boat along fine in all weather. When we got the motor we made sure we got the motor with the inbuilt fuel tank as well as the remote fuel tank. We find that when we are club racing we use the inbuilt fuel tank more than the remote tank. The inbuilt tank holds a few liters of fuel and will run for over an hour on that tank alone.
I had an 8hp merc on my '24 which was very good crossing Moreton Bay when sailing wasn't an option. I now kave a '28 and am using the same engine, strangely the '28 seems to move a bit faster than the '24 did??