reduced power output

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Davef

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Hi

since wrapping a piece of plastic round my prop I have suffered a lack of power. the engine revs freely under no load but when I engage forward or reverse I only get circa 1500 revs, this gives me a maximum speed of just under 3 knots when I used to get 6+. I have a 22' westerly nomad with volvol penta 2001 engine and a MS2B gearbox.
The offending plastic has been removed to no avail,:mad: I was told it could be the semi rigid flexi coupling which I have now replaced with a RD coupling and some ingenious engineering work to fill the gap. All now replaced but still no difference in the power output. If I disconnect the Shaft it revs freely under load.
I was wondering if it could be the rope cutter acting as a brake but the prop turns by hand in neutral ? back in the water now unfortunately but does anyone have any ideas what the problem may be ?
thanks
D
 
Check the coupling on the shaft could be slipping or the prop loose on the shaft.
The cones in the gearbox may be worn.


Please disregard this load of rubbish as I did not read the original post!
 
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scottie said:
Check the coupling on the shaft could be slipping or the prop loose on the shaft.
The cones in the gearbox may be worn.
Click to expand...

They would not limit the engine revs

No suggestions to make though.
 
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I'm no expert here, but from recent and current investigations into my own (gearbox) problem, worn cones in the box would/does not limit the revs - so i agree with Vics. It would however impact on bite/thrust through the water.
At least you can rule something out - if not something in at this point !
Jaba
 
All I can add is that my related experience was of a bearing in the gearbox heading for eventual seizure. Have you tried to rotate the propshaft by hand with the gearbox in neutral? If that is OK then you can concentrate on the engine side of things.
As you know in boating 2+2=5 and the usual cause of limited revs under load is fuel blockage which may be completely coincidental.
 
thanks for the input

Thanks all for you advice and comments, to answer your questions there is black smoke on start up for about 2-3 mins then goes to normal ! no distortion of either the shaft or Prop and very little lateral movement when spinning. and when in Neutral the prop turns relatively freely !

thanks
 
What sort of rope cutter do you have? Messing about with the coupling could have altered the position of the cutter in relation to the rest of the stern gear and it could be binding when the engine moves forward on its mountings in forward gear. Plastic bags round props can also lead to plastic melting on the shaft and in the cutless. Needs sorting quickly as you could wreck the cutter and or cutless. Dry out if you can and check the clearnces of the cutter.
 
As has been suggested, these symptoms are often caused by blockages in the fuel supply, for example diesel bug in the filters. I have experienced it both on a friend's boat and in an old Mercedes van. Engines revved freely in neutral but had no power nor revs when driving. In the van we did 30 mph for about 60 miles on the M6.
 
You obviously have to make sure that the shaft, prop, rope cutter are all freely rotating .

The black smoke issue, or lack of, is worth revisiting.
Ignore any smoke at start up.
With the engine warmed up and the boat under way, How much smoke do you get at full throttle? If it smokes more heavily than you would have expected at 1500 rpm then it indicates load on the engine preventing it reaching its normal max revs. Look further at the shaft etc.

If there is no more smoke than you would normally expect at 1500 rpm then it's almost ceratinly an engine problem...... very possibly something restricting fuel flow ... or a mechanical problem with linkages, governor, injector pump etc.

Like Vyv and his old van I have experienced very similar with my diesel car due to a blocked fuel filter.
 
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Davef said:
Hi

since wrapping a piece of plastic round my prop I have suffered a lack of power. the engine revs freely under no load but when I engage forward or reverse I only get circa 1500 revs, this gives me a maximum speed of just under 3 knots when I used to get 6+. I have a 22' westerly nomad with volvol penta 2001 engine and a MS2B gearbox.
The offending plastic has been removed to no avail,:mad: I was told it could be the semi rigid flexi coupling which I have now replaced with a RD coupling and some ingenious engineering work to fill the gap. All now replaced but still no difference in the power output. If I disconnect the Shaft it revs freely under load.
I was wondering if it could be the rope cutter acting as a brake but the prop turns by hand in neutral ? back in the water now unfortunately but does anyone have any ideas what the problem may be ?
thanks
D
Click to expand...

Not sure whether they are fitted to shaft drives but I once had this problem with a 50HP Mercury. Turned out that the prop connected to its drive shaft through a metalastik bush. The bush had perished and although the shaft turned okay it slipped whenever under load. New prop, fixed. :)

Just thought. If it's an older boat. If 1500RPM is not the max design speed of the engine it may be your governor. It may also be mucky fuel. A problem I have to deal with myself.
 
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Thanks again...

I have already changed the fuel and oil filters on the engine but I will change the primary fuel filter tomorrow and see if that improves it ! hopefully it is a fuel issue, if it turns out to be fuel starvation / blockage I will be happy whilst at the same time slightly annoyed :) having spent nearly £500 with lift out new flexi-coupling and bespoke manufactured drive shaft extension.

Hey but that's sailing for you, incidentally the smoke is normal at full (reduced) revs I did also disassemble clean and replace the rope cutter which is a 'gator' type it did turn freely but was a little stiff, I take your point about it potentially catching so that's why i had the driveshaft extension made to give the same clearances as before.

Thanks again all, I will let you know how it goes
 
stuhaynes said:
Not sure whether they are fitted to shaft drives but I once had this problem with a 50HP Mercury. Turned out that the prop connected to its drive shaft through a metalastik bush. The bush had perished and although the shaft turned okay it slipped whenever under load. New prop, fixed. :)

Just thought. If it's an older boat. If 1500RPM is not the max design speed of the engine it may be your governor. It may also be mucky fuel. A problem I have to deal with myself.
Click to expand...

I think you will find the max revs of the engine are given as 3200 rpm.

Thinking a little more. If it was the governor out of adjustment it would limit the revs even with no load on.

Hopefully it will still do 3200 with no load?
 
One thing you might check is the fore and aft movement of the shaft. You said the shaft rotated freely, does it still rotate freely if you pull the shaft as hard forwards as you can as you try to rotate it. Also have you checked to see if you get the same results going hard astern.
 
fuel filter changed :) once I got it bled and started still no difference so thinking it must be the gear box? once disconnected the shaft moves backwards and forward and turns freely at each position except if its pulled in to far when the rope cutter jams on the Pclamp, in the normal position it rotates freely. will try removing the cutter altogether then if that doesn't work get a compression test, if that's Ok I will take the gearbox apart to see if that's the problem :mad:
 
Lack of clearance on the cutter is almost certainly the problem. Running hard against the block will cause friction, wreck the bearings and start wearing away the faces of the cutter. Sounds like you got the sums wrong when putting in your new coupling - easily done.
 
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