Engine swap

[Chianti]

Hi I am new to boating
I’ve bought a picton spirit 3000 with twin petrol engines which have been removed I want to replace the engines with a single nanni 50hp I also want to convert it into shaft drive and was wondering what people think of the hydraulic drive set up

[Sailmonkey]

Are you able to do all of this work yourself?

If no, you’ll be into this little experiment for far more than the boat is worth.

[GordMay]

Greetings and welcome aboard the CF, Chianti.


“... As to overall efficiency, do not kid yourself. In the best case scenarios, working with closed loop systems operating at peak efficiencies and pressures, you may see 80-82% at best, but 50-70% overall would be the norm. So if you go hydraulics, don’t do it because you think you are going to have a more efficient way as to transmitting power from an engine to the prop, you won’t. Do it for other reasons ...”
Excerpted from "Some Tips & Experiences on Hydraulically Driven Sailboats" ➥ https://www.sbmar.com/articles/some-...iven-sailboats

[Lepke]

I was a commercial fisherman and used hydraulics every day. It's a great way to transmit power, but sucks up a lot of HP. Pumps, motors, hoses, valves and seals all have a life span that is shorter than the average transmission. Permanent installations are plumbed in steel pipe. And even steel pipe can only go thru so many pressure changes. It flexes every time it takes up pressure, eventually becoming fatigued.
I also owned diesel electric tugs and that would be my preferred system for non-direct drive. But it has losses, too and is expensive.
Your boat had about 200hp engines. A single 50 hp diesel is going to push it at a little over hull speed. Maybe 8-9 knots.

[Chianti]

Thanks for reply it’s only going to be a river cruiser max speed about 6 knots so should be fine

[FAST FRED]

The huge hassle and expense will be converting from two engines to a single centerline prop.


Perhaps 2 15 hp diesels would be less expensive?


If it was an I-O, two 20 hp outboards would work fine.