Motor runs well but little forward propulsion?

[SteelCruiser]

Lister Petter STW3

Years ago, would comfortably run at 5.5kts
* calm seas - no wind *

Motor been running well yet slowly, over time, little by little forward propulsion has got less ( speed over ground as per GPS )
Put it down to wind ahead, tide, growth on hull etc etc

Yesterday, punching into 20 kt head wind, we were making only 2.2 kts, then 1.8 yet the wind was easing?

I tried to move the ‘Forward / reverse’ lever into nuetral?
It was jammed.
Down below, the connection between that lever and the gearbox also has a long round bar attached directly out of the gear box ( see photo’s = the rusty bar )

This bar was jammed solid against the cooling water pipes exiting the engine. I could, with difficulty, move that bar by hand. Speed increased noticeably - from 1.4 kts to 2.2 .

Still not flash, but improvement.
Yet, within one our, approaching the mooring thankfully, speed over the ground was down to only half a knot, with the engine running ‘flat out’.

Remember

A nights sleep.
Look again and see ‘Gulp’...
That long round bar is doing its best to ‘chew through’ those water cooling pipe connectors. *see photos*
That could easily lead to overheating and a seized motor.

I have just cut 6” off that bar. No longer hitting, yet no improvement.

Hmmm.
Questions, comments - suggestions?


https://imgur.com/gallery/sVL5zJP

[SteelCruiser]

[SteelCruiser]

[SteelCruiser]

[Compass790]

From yr symptoms you may have a slipping clutch. You have to adjust the" throw " on your gear change mechanism so that it pushes the clutch in harder.
We had a Lister Petter but a different model that had a terrible cone clutch in it that had similar symptoms but with other problems as well.
If you try pushing fwd on that handle you cut off & it speeds up it points to clutch engagement issues. Try slamming the lever forward with a fast hard motion at low revs at the same time as you use your cockpit control to shift into fwd & hold it in firmly as you speed up. Of course you need 2 people.

Does it have a name on the gearbox? It might jog my memory if it's the same style as the Phillipines manufactured one we had.

[Sailmonkey]

My take, it’s time to pull the gearbox and rebuild the clutch cones/dogs. After running like you describe I’d be amazed if there was any bronze left on the clutch faces. If you change the gear oil I’ll bet it looks like black bass boat sparkle.

[winschwab]

Sounds like mechanical problem, but please check your prop. Growth on prop can reduce forward propulsion to zero.

[duckpond49]

Didn't see any Mfg names but I had a similar problem a few years back with my VP setup.
The splines on the flywheel/trans shaft had worn out so shaft slipping and then quit turning. Turns out a common problem on 3 cyl. VP's:"hammering" of the torque on the shaft and splines. The parts were gonna be over 3G's (thank you VP). I found a great solution from a Brit source for $2700 less.

Good luck!

[mholtzberg]

Sounds like mechanical problem, but please check your prop. Growth on prop can reduce forward propulsion to zero. +1

[Scubaseas]

Assuming you prop is not totally fouled it sounds like a cone clutch is worn. Drain the transmission oil and look for brass dust or clutch material (looks like brown flour). Who makes the transmission? If it has fiber clutches you might buy some time with Lucas Stop Slip but the right way is to rebuild it.

[SteelCruiser]

prop not foul.

the Prop spins freely in neutral.
Today I will put in ‘Fwrd’, then jump into water and see if the prop still turns. Q. It ought not turn then = correct?

Is there any possibility there could be a ‘key way’, holding the prop on, that is sheared, allowing the prop to spin , in gear?

[Scubaseas]

How is it in reverse? If it was a split key or worn spline on the prop it should be the same fwd or rev. If rev works OK then likely an internal problem with fwd gear clutch.

[SteelCruiser]

reverse is no different -

[Scubaseas]

What transmission is it? Is it hydraulic and/or low on fluid?

[Fonseca]

Originally Posted by SteelCruiser

Attachment 234292

Excess of fouling on the hull.