Forums, Engine, Gearbox, Stern Gear, etc, 20 vs 25hp

Speedwell at 15/11/2019 19:58:04
How much difference does a 25hp vs 20hp Yanmar make to performance, I’ve always found the 20 a little underpowered in the Solent. I may have to replace the gearbox on Speedwell and thinking of going the whole hog and re-engining with a 25. Would welcome any thoughts.

SealionK5199 at 19/12/2019 11:55:57
I have an 18hp Perkins Perama which I found underpowered when trying to motor into any choppy seas. Last winter I changed from a 2 blade fixed prop to a 3 blade feathering Darglow prop. The boat now keeps momentum through the chop instead of being stalled by the waves. The new prop feels like it gets a much better grip on the water, seems a lot quicker to grip in reverse too. Not cheap but I’m happy with the change.

Conor

Simon Begley at 20/12/2019 19:49:11

We also have an 18hp Perkins Perama.
It was ok when we had a 3 blade Darglow prop. We changed to a fixed 2 blade a couple of years ago when the Darglow was very worn and sometimes refusing to un-feather. Since then we’ve struggled punching into a chop.

I don’t think the problem is lack of horse power.

Given the size of the orifice, we’re limited with prop size and the extra power might not be much use. It’s very important to match the propeller pitch to the engine power, revs and gearbox reduction. I’m going to have our prop re-pitched this winter and see if there is any improvement.

Alan Dixon at 06/01/2020 14:31:58
I fitted a 25hp with a 9 × 14 3 bladed prop some 15 years ago now. majority of the time have not needed the extra power, but on the odd occasion, when it hits the fan, I have been extremely grateful for the extra 5hp

George Isted at 03/02/2020 20:07:05
Hi Red (speedwell),
it may be worth checking the pitch on your prop in case it needs increasing as going from fast-ahead to fast astern can damage the pitch-stops on a darglow but this is fixable. What speed can you achieve with a clean bottom and prop and can the engine reach maximum RPM (3600 for a 2GM20 I think).

It could also be that your engine needs a birthday and a top-end rebuild may restore some horses that have escaped.

The Yanmar 2GM’s a great little engine and I never felt under-powered with it on Concerto.

If you want to speak about it feel free to call.

George