I had 2 - 70 hp Suzukis on a 20 ft cuddy. They weighed in at 375 each.

I was well below my listed hp. of 200 but the motors were heavy. I had to put an auto-switch bilge pump in the transoms well to keep the splash-over out. They had to cut the transom to fit the motors on. I didn't realize how much lower it would be.

I won't do that again. Nice to have the 2 motors but the weight was a little too much. I put up with it for years though.

I think weight is more of a issue than hp. but I wouldn't put a 250 hp. on an 18' skiff.