15 hp Yamaha 2 stroke

Scooby · 26 July 2021, 20:40

New boat arrived had to keep my original engine due to costs involved.
Top speed 20 mph 4992 rpm at wot
Is this acceptable or wil I need to lower the prop pitch. any help appreciated

TmMorris · 26 July 2021, 21:27

Seems pretty good. Depends on the boat. I've quite a draggy Excel 390 and run a 15 yam 2 stroke and get about 15 knots, so 18mph with myself, two children and a bit of kit.

Scooby · 26 July 2021, 21:37

It's a quicksilver 3.8 ALU hull rib 92 kg
Boat

Fenlander · 26 July 2021, 21:59

What pitch do you have at the moment?

Scooby · 26 July 2021, 22:11

Duel thrust 9.75 X 8 was thinking about getting 9.75 x 6.5 to get the rpm up
But don't want to sacrifice top end speed 15 hp probably too small but will have to wait till next year for new engine

Fenlander · 26 July 2021, 22:32

Post #33 on this thread of mine might be of interest...

https://www.rib.net/forum/f36/yamaha...ice-81611.html

So you have the same length boat as us in that trial... yours weighs almost twice as much but should have a far more slippery hull and you had the same HP outboard. In mph we made 20.6 maximum two up with a Yamaha OE 9.75" pitch.

I would be amazed if you needed a 6.5" pitch but if you mean you have the paddle wheel style prop with enhanced reverse thrust they will give odd results and aren't ideal for your boat.

Scooby · 26 July 2021, 23:03

My mistake current prop is 9.75 diameter X 8" pitch high thrust