My honwave is a 2.8 rated to 8hp and I have a 15hp 2 stroke on it - I'm sure there are several good reasons why it's rated to 8hp but as far as I'm concerned the engine is pushing the transom that pushes the boat body, the most resistance and strain is getting it up on the plain, the rated hp engine could get it on the plain so other than weight which my one is under the rated kg the only danger of over power is the design speed.
Like everyone says it's a case of being careful, I love my 2.8 with 15hp and it is very quick but I'm sure it could be dangerous if I was reckless with the throttle.
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