What's the minimum horsepower required for a boat to be able to plane?

Question

I want to build an aluminium planing boat for three occupants, length about 5 to 6 metres, with a light and low, but fully enclosed, aluminium cabin.
It's supposed to be a commuter boat for use on the Otago Harbour in southern New Zealand.
I want to be able to plane, but the speed limit is 25 knots - which I hope to reach, give or take about 8 knots. I like the idea of using a Yanmar Diesel outboard motor. They come with up to 39 horsepower. Would I need that much?
Thanks.

Answer 1

I would say you have a hope in hell. For a boat that size, and this would be the min I would say 90hp, if your goping out in swell or rough condistions etc then a min of 115, what is the boat rated for that will give you an idea.

Answer 2

I think that a yanmar 39 hp is perfect for your boat. Yes I think you will need all 39 horsepower to reach around 25 knots. Your boat should plane out at about 20 knots If you keep it light. I have used boats like the one you are building and this is my experance. Captain jamie at http://www.boatboss.com

Answer 3

39 HP should be ample but if you are building the boat yourself from scratch then you may want to consider fitting trim tabs which would get you on the plane at lower speed and make the baot more stable.

Answer 4

You are going to have to submit a lot more details to get a
correct answer to this one , wt ,type of hull , and water
conditions etc..type of construction design. strength of transom
be careful if you are building from scratch , Research!!! .
the rule of thumb here would be over strenghten the design
and slightly overpower it , Always better to have too much than not enough..

Answer 5

Planing depends on the conditions and the hull shape and the weight as well as the speed. Get info on hull shape for planing.