Originally Posted by Jeremy Fry
Is there a easy calculation for working out what engine size you need?
On a 5.8M RIB what is the minimum size engine needed to allow teenagers to wakeboard, on a flattish sea, with perhaps 3 in the boat at the same time?
Is it simply - the bigger the better, or is there some science to it?
What boat is it Jeremy?
What is its max rated HP?
Some manufacturers will rate their boats for more power than others - whether it's appropriate or not. So max rated HP may not tell the complete story. For example, many Cobras seem to be powered with larger engines than other similar size RIBs.
My 6.5m Scorpion was originally supplied with a 90hp 2-stroke and apparently would do mid 30 knots lightly loaded. When I bought it it already had the 150hp. The big engine is great when heavily loaded 6-8 people and I think a smaller lump would have struggled a bit.
The hull form and construction will also have a bearing on what's appropriate. I had some friends with two similar size RIBs. One was an Avon D560, the other a Ribtec 585. Both had the same 100hp Yamaha 4 stroke.
The Avon was lightly built and had a flat hull. In all but flat water 100hp was "more than enough", possibly too much.
The heavily built, deeper V Ribtec would have benefited from more power.
For your use you'll want to have "enough" power. I don't wakeboard so don't know how much is "enough".
Perhaps someone who wakeboards from their RIB can chip in?