Forums, Engine, Gearbox, Stern Gear, etc, Speed & Revs

Speedwell at 07/10/2016 20:05:34

I am getting about 4.5-5.0KTS from our ~20yo Yanmar 2GM20 and Darglow 3-blade folding prop. The engine appears in good condition and well maintained. We have no rev counter so I estimate what feels right for the engine, but since on one occasion I ended up with a sooty transom I am nervous about over-revving.

What speed should we be getting with this setup and what methods do people use for estimating the correct power settings without a techo?

Many thanks

George Isted at 07/10/2016 20:41:21
4.5-5kts through the water is comfortable on Concerto with exactly the same engine and prop, it’s about 2400rpm. I can get the boat to go faster but it gets loud, produces smoke and burns lots of fuel for a small increase in speed.

With a clean bottom and prop she will do about 6.5kts flat out in flat water but I don’t do this as a matter of course.

That said the engine does like to be worked reasonably hard and a decent period of motoring at higher rpm is good for the engine every now and again. It clears out carbon deposits and mine always runs sweetly after.

If you want a cheap tacho take a look at the tinytach http://www.tinytachuk.com/ I don’t have one but I’m told they are good.

If you are getting excessive black smoke it could be the prop/hull is grubby or the prop has slightly too-course a pitch.

Speedwell at 07/10/2016 22:05:03
Thanks George. Seems like I’m in the right ballpark. I was expecting 5.5KTS without pushing too hard but we always speed up when the sails are up.
I’ll give the Italian tune-up a go!