Engine problem or fouled prop???

Daydream believer said:
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.
Click to expand...

+1

I've been wracking my memory for what I've observed over the years .....

The problem is that he has :

1. 50% reduction in boat speed from 8 to 4kts.
2. Engine RPM apparent drop from 2800-3000 to 1800
3. More than 1/2 throttle no increase in speed or engine RPM - but sooty black smoke

They are so like when I picked up that bit of cargo net going up river to Newport IoW ..... the RPM I cannot compare as I do not have Rev counter - but I remember a marked reduction and distinct lack of throttle + smoke when I was pumping in fuel that just didn't do anything except smoke !!

Of course there are various other reasons it could be ... only a serious look at all will get answer .... If I was close to OP - I would lend my underwater camera system ... its a fishermans system ... (cable to a WiFi box ..... so your phone is the screen).

If boat is a bilge / triple keeler - then its easy to dry out and have a BBQ day as well as check prop ... but if a Long Keeler / Fin job - then its find scrubbing piles and and check out at low tide ...
 
By a fouled prop I don’t mean rope or similar getting wrapped round it. That’d tend to stop the motor dead rather than restricting the speed, although a mess like refueller showed would slow the prop down. What I’m referring to is an accumulation of growth on the prop itself, usually coral worms or barnacles. That has the twin effect of wrecking the hydrodynamic efficiency of the prop and increasing the drag in turning the prop itself. That means the engine won’t turn the prop as fast as normal and the boat speed will be reduced.
I spent a winter in Barcelona marina: we left in April and needed to use full throttle to make our usual cruising speed as opposed to perhaps three quarters open. We also burnt about twice as much fuel as normal. On arriving off Mallorca I dived to check the prop and found it was well covered with coral worm. Cleaned that off and things were back to normal.
I also helped a mate change his exhaust elbow but the symptoms he had were different. He couldn’t get the engine to rev even out of gear. The elbow was clogged to the extent of not being able to fit a finger through it.
 
My bet would be on a partially blocked exhaust elbow, as your symptoms are exactly as I experienced when mine was blocked a few years ago.
 
Thanks for all the responses so far.

Firstly, I have tried removing the air cleaner and unfortunately it made no difference so it's not a blocked air filter.

I don't believe it is fuel starvation either - the strong smelling exhaust fumes at full throttle are probably due to unburnt fuel. I also changed both diesel filters in January and the old ones had no sign of dirt or debris.

Partially blocked exhaust elbow could be a good suggestion - I will explore that one next time I'm at the boat (later next week).

Apart from that I still think fouled propeller is the best contender. I could really do with a friendly diver to take a look as I tried underwater cameras some years ago without much luck. You need a 12' pole to reach the (saildrive) prop from the pontoon (4m beam, 2.1m draft) and the water in Port Solent is pretty murky. An inspection and photos by a professional diver is £200+ last time I enquired and a lift and hold will be even more so I want to complete all possible engine checks before I resort to a big money outlay. I have my annual lift-out booked for May but may have to bring that forward.

Before I do, though, does anyone have any other serious suggestion for possible engine faults that would match my symptoms?
 
I an 73 years old & i dived under my boat to remove a net from my saildrive when in Middleburgh. The boat was on the pontoon.
I wore a shortie wetsuit and a pair of goggles. A shortie wetsuit is cheap & I keep one aboard. A full length oneis not necessary but protects the skin. (handy if you have to partially beach the boat on a sandy shore to do it & have to wade in water) Some flippers would have been handy. I did keep floating up, so I have now purchased a weight belt with a quick release buckle to help me get down quickly. Then release it to come up quick.
I did not have a rope to pull me up, but I do have ropes suspended each side of the boat to pull me along. All you need to do is get between boat & pontoon opposite the saildrive with the crew holding the boat 3 feet off (I was on my own so only had 18 inches) then using the pontoon, invert yourself & give a good push from the pontoon to get down. You should be able to hold your breath for 1 minute which is more than enough to see the prop. I had to get within 18 inches to see it.
I managed to get the net off easily. But if you get to the prop you can have a look then you will know if it is OK. Then you can decide if it is worth paying a diver, or having a liftout. You might manage it yourself with a bread knife if it is rope.
I am not fit by any means & cannot swim the length of the boat so used ropes suspended along the side to work my way along the hull to the pontoon steps. If you have a crew to help it will be easy enough. The experience is worth it.
You could ground the boat very near LW. so it does not go right over but is in 5-6 ft of water where you can stand on the bottom, then nip over & have a look.
 
Hi Samuel
I'm 75 years old (not that that is relevant - yet) but have a perforated eardrum that renders all underwater activity a definite no-no. Shame as that would be the easiest (and cheapest) solution but I've learned to live with it over the last 70 years (and several failed ops to fix it). Your underwater camera would have been useful - the one I tried was a cheapie and the pole was inadequate. There are better versions of both around now, no doubt.
Leaning on the piles is also a good (and cheap!) solution but I have been warned that the keel profile and weight distribution on my type of boat is not good. An earlier model was apparently not recommended for use on the Sealift (which is another option I have currently rejected)
If I can't find anything at fault in the engine department I think bringing forward the annual lift-out will be the best solution. Unfortunately, I dislike doing all the necessary work (it's a 40 footer) in the cold and wet! I was also hoping to enjoy several rallies at the end of March and through April. The joys of boating, eh!
 
Instead of asking commercial diver .... find local diving club ... a donation to their club kitty is often enough ..
You may have to be outside your marina to have a club guy ... as many marinas are against having 'amateurs' play in 'their waters' ....
 
Have you managed to find out whether the prop will turn freely by hand yet?

In my boat I can get at the propshaft inside the boat to check this out, out of gear obviously.

If it's a sail drive I don't know how you'd do that.
 
Daydream believer said:
I an 73 years old & i dived under my boat to remove a net from my saildrive when in Middleburgh. The boat was on the pontoon.
I wore a shortie wetsuit and a pair of goggles. A shortie wetsuit is cheap & I keep one aboard. A full length oneis not necessary but protects the skin. (handy if you have to partially beach the boat on a sandy shore to do it & have to wade in water) Some flippers would have been handy. I did keep floating up, so I have now purchased a weight belt with a quick release buckle to help me get down quickly. Then release it to come up quick.
I did not have a rope to pull me up, but I do have ropes suspended each side of the boat to pull me along. All you need to do is get between boat & pontoon opposite the saildrive with the crew holding the boat 3 feet off (I was on my own so only had 18 inches) then using the pontoon, invert yourself & give a good push from the pontoon to get down. You should be able to hold your breath for 1 minute which is more than enough to see the prop. I had to get within 18 inches to see it.
I managed to get the net off easily. But if you get to the prop you can have a look then you will know if it is OK. Then you can decide if it is worth paying a diver, or having a liftout. You might manage it yourself with a bread knife if it is rope.
I am not fit by any means & cannot swim the length of the boat so used ropes suspended along the side to work my way along the hull to the pontoon steps. If you have a crew to help it will be easy enough. The experience is worth it.
You could ground the boat very near LW. so it does not go right over but is in 5-6 ft of water where you can stand on the bottom, then nip over & have a look.
Click to expand...

As a non-expert, I wouldn't want to dive under my boat at the moment - the water's a tad chilly! Standing on the bottom doesn't work well in Portsmouth Harbour either, you'll just sink into the mud.

In the OP's position, I'd check the exhaust elbow and pipe as a virtually zero cost option. If they're OK, I'd go over to Hardway and book a scrubbing grid on the next spring tide. They have a concrete bottom and good strong posts to lean against, and it'll be a lot cheaper than a lift.
 
James_Calvert said:
Have you managed to find out whether the prop will turn freely by hand yet?
Click to expand...
It's a sail drive so not possible.
Next thing to investigate is the exhaust elbow - should be straightforward to check that out. If it's not that, then I'll bring forward the annual lift out (currently scheduled for the warmer weather in May) if I can get a slot - the boatyard is pretty busy in the run up to Easter.
 
Its probably the prop but exhaust elbows can block suddenly. Mud sucked in as silt can set solid on the walls and the last bit of flow can cease as the cooling engine from the last run has baked the final slurry to a brick. More common in muddy waters of the Bristol Channel but I see no reason why Solent should be immune - its not crystal clear
 
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