Engine problem or fouled prop???

[Playtime]

My 8 year old AWB has a Volvo D2-40 with approx 700 hours use and a Flex-o-Fold folding prop.
With the engine in gear the maximum achievable revs at full throttle used to be between 2800 and 3000 rpm, giving a boat speed of around 8 kts. On Wednesday the maximum achievable rpm (in gear) was 1800 at about 1/2 throttle. Increasing the throttle further resulted in black (sooty??) water from the exhaust and some strong smelling smoke but no increase in rpm. Maximum boat speed was around 4 kts.
The lack of thrust was so bad that we failed to exit Portsmouth Harbour against the Spring flood (4.5 kts) and had to spend the morning sailing in the harbour rather than enjoying a good thrash in the Solent. Speed under sail was not affected i.e. the hull is reasonably clean.

The collective opinion of the crew (all yacht owners) was engine overload due to a badly fouled propeller; one mentioned coral worm as a possible cause, but I berth in Port Solent which hasn't previously had a coral worm problem (AFAIK). However, subsequent test have shown good prop wash in forward gear and around 2kts past the log impeller in reverse at 1800 rpm.

Someone else suggested a blocked air filter so I removed the filter this morning but it made no difference. Another suggestion is a partially blocked exhaust elbow; I haven't checked that yet.

Has anyone else suffered this problem or have any other suggestions that could account for these symptoms (e.g. injection pump, injectors, governor etc.)?

 

[[70521]]

When did you last inspect the prop?

Look at one thing at a time and eliminate that before moving onto something else.

 

[duncan99210]

It sounds very much a fouled prop. Easy enough to check that with a GoPro on a stick. If you've got a clean prop then the next thing to check is the exhaust elbow.

 

[richardbrennan]

If it is the engine rather than the prop, I would have thought the exhaust elbow the most likely candidate and certainly where to start. I had a loss of top end rpm, albeit not quite so dramatic, on my D1-30 at about 600 hours.

 

[Daydream believer]

Prop problem, unless this has developed in the engine over time & you have not realised. An engine does not normally loose revs for air filter & exhaust elbow suddenly. They are things that gradually reduce performance as the situation develops. My elbow lasted 3000 hours & I changed it because I noticed only a slight drop in power, not because I had a sudden drop in performance.
If you have had the boat standing still for some time then prop fouling could be the problem. May even have a polythene bag or similar round it to add to the weed such that the prop is partially open

 

[Beneteau381]

My 8 year old AWB has a Volvo D2-40 with approx 700 hours use and a Flex-o-Fold folding prop.
With the engine in gear the maximum achievable revs at full throttle used to be between 2800 and 3000 rpm, giving a boat speed of around 8 kts. On Wednesday the maximum achievable rpm (in gear) was 1800 at about 1/2 throttle. Increasing the throttle further resulted in black (sooty??) water from the exhaust and some strong smelling smoke but no increase in rpm. Maximum boat speed was around 4 kts.
The lack of thrust was so bad that we failed to exit Portsmouth Harbour against the Spring flood (4.5 kts) and had to spend the morning sailing in the harbour rather than enjoying a good thrash in the Solent. Speed under sail was not affected i.e. the hull is reasonably clean.

The collective opinion of the crew (all yacht owners) was engine overload due to a badly fouled propeller; one mentioned coral worm as a possible cause, but I berth in Port Solent which hasn't previously had a coral worm problem (AFAIK). However, subsequent test have shown good prop wash in forward gear and around 2kts past the log impeller in reverse at 1800 rpm.

Someone else suggested a blocked air filter so I removed the filter this morning but it made no difference. Another suggestion is a partially blocked exhaust elbow; I haven't checked that yet.

Has anyone else suffered this problem or have any other suggestions that could account for these symptoms (e.g. injection pump, injectors, governor etc.)?

A fouled prop doesnt overload the engine, Because it loses efficiency it does the opposite. A bit like a feathered airplane prop. Check that the prop shaft turns easily by hand, you might have a rope or such like around it. A blocked exhaust can cause the same symptoms.

 

[Daydream believer]

A fouled prop doesnt overload the engine, Because it loses efficiency it does the opposite. A bit like a feathered airplane prop. Check that the prop shaft turns easily by hand, you might have a rope or such like around it. A blocked exhaust can cause the same symptoms.

An exhaust blocks slowly. It would not suddenly become blocked. It would gradually coke up- would it not?
You can rotate a prop shaft with weed on it by hand but once you try to spin it then it becomes a huge centrifugal force. If the weed or whatever is fairly evenly balanced it will not shudder very much. Polythen tends to wrap itself evenly around the shaft & bind in between prop & P bracket, or sail drive, forming a brake, reducing revs. A rope cutter will not remove it because it gets "stringy". The prop will not fully open, thus reduce forward motion.
I know this because it has happened to me twice causing the clutch to slip badly

 

[Refueler]

That caused serious reduction in rpm and speed ... I tried reverse / fwd / reverse but it just would not clear ...

Alongside (Newport IoW) ... and tide went out ... it literally fell off once I touched it with boathook !! No I did not leave it in the mud for another to pick up !!

 

[Refueler]

Its been mentioned that Rope Cutters cannot often handle such ... and that is true - especially like my rope snagged - it binds itself in front of prop and then literally welds itself in place ... it can in fact if run for too long cause damage to the shaft.

 

[Bobc]

Dirty prop and dirty bottom

 

[Refueler]

Increasing the throttle further resulted in black (sooty??) water from the exhaust and some strong smelling smoke

That is basically because you are throwing high volume of fuel into engine but its not increasing rpm as a result ... you are getting partially burnt fuel mixed with carbon .....

My 4-107 is far too powerful for my 25ftr ... and if I open throttle to more than 75% - then all I get is black crap out the back and a serious amount of cleaning of transom to do !! where the black sooty smoke stains the stern..... because there's not enough load on prop for the fuel going in .. so partially burnt fuel.

 

[Iliade]

If the prop is clean remove the air filter and try again...

 

[Iliade]

Refueler, That is an issue with the motor's air intake (most likely), injectors, bores, valves or prop, not because the motor is too powerful. If that were the case the stern would dig in and you'd see a rooster tail, but the exhaust gases would remain clean.

 

[Pye_End]

A fouled prop doesnt overload the engine, Because it loses efficiency it does the opposite. A bit like a feathered airplane prop. Check that the prop shaft turns easily by hand, you might have a rope or such like around it. A blocked exhaust can cause the same symptoms.

If true, why does a fouled prop restrict max rpm?

 

[Refueler]

Refueler, That is an issue with the motor's air intake (most likely), injectors, bores, valves or prop, not because the motor is too powerful. If that were the case the stern would dig in and you'd see a rooster tail, but the exhaust gases would remain clean.

Sorry ... you don't know my boat and you are wrong.

1. My stern does dig in and in fact I have to close my cockpit drains otherwise I get wet feet.
2. I can create the biggest wake you've ever seen of a sail boat ... she gets just over 9kts ... 4 ton 25ft ...... engine is 43HP

The prop is the one from my previous Perkins of about 35HP ..... but because the boat is a pig going astern due to prop size - it was decided not to up the size to suit the 43HP ....

My statement is based on not just one - but two extremely experienced diesel engineers who have known my boat and worked on it ...

 

[Refueler]

If true, why does a fouled prop restrict max rpm?

The photo I uploaded earlier of my fouled prop - that ropework round my shaft and prop cut my revs seriously and speed was seriously reduced ...

 

[LittleSister]

An exhaust blocks slowly.

It does if coking up is the issue but, though less likely, there have been cases mentioned on the forum of the inside of exhaust hoses collapsing and causing blockage.

 

[Refueler]

It does if coking up is the issue but, though less likely, there have been cases mentioned on the forum of the inside of exhaust hoses collapsing and causing blockage.

Correct ... particularly the double wall type where the inner heat resistant 'rubber' breaks down and often blocks the pipe ... causing excessive back-pressure.

 

[QBhoy]

More likely a fouled hull, leaking injector or similar

 

[Daydream believer]

It does if coking up is the issue but, though less likely, there have been cases mentioned on the forum of the inside of exhaust hoses collapsing and causing blockage.

Fair comment, but I was referring to the exhaust elbow where the cooling water enters the exhaust system. Perhaps i should have made that clear.
From the OP's post it would suggest something more "sudden" that is why I suggest that if the boat has been left, then fouling could ( Note- Could) be the problem. He returned to the boat & noticed a marked difference in engine & boat performance. Not a gradual one. Refueller's picture demonstrates what I was suggesting: But it is only a suggestion. Time will tell.