So a little help please..!

ST840

ST840

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Coming back from fishing yesterday, we had a bit of a loss of speed when entering Southampton water. Engine revs ok but knots were down. Some vibration was heard that was defo not normal.
After a couple of mins we managed to get up to 15 knotts and get back to the berth.
I dived under today and noted that when prop is wiggled clock wise to anti clockwise there is a slight tapping sound. Prop nut is tight, anode is loose but the bolt tight. So loose because of degradation.
My concern is the "P" bracket gland has failed.
It's a shaft drive boat, any ideas ??
 
Reach down to the shaft in the bilge and check for play (all directions).

Turn it by hand - it should have some resistance but turn. Cutlass bearing would sound different if too tight (I had one anode coming loose on the shaft and sliding back to the P-bracket, limiting water flow eventually making the cutlass sound bad at low speed and making the engine sound loaded).

Replaced both. Not too hard but took some effort to make the tool (as I didn't want to buy/hire a proper tool).

Edit: If same as mine you have a hose pushing water into the shaft bearing at the gearbox end. Check that one also.

Also check flange bolts on the gearbox and the shaft coupling. Might need an assistant to help when you push/pull/turn the prop.
 
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ChromeDome said:
Reach down to the shaft in the bilge and check for play (all directions).

Turn it by hand - it should have some resistance but turn. Cutlass bearing would sound different if too tight (I had one anode coming loose on the shaft and sliding back to the P-bracket, limiting water flow eventually making the cutlass sound bad at low speed and making the engine sound loaded).

Replaced both. Not too hard but took some effort to make the tool (as I didn't want to buy/hire a proper tool).

Edit: If same as mine you have a hose pushing water into the shaft bearing at the gearbox end. Check that one also.

Also check flange bolts on the gearbox and the shaft coupling. Might need an assistant to help when you push/pull/turn the prop.
Click to expand...
Ok thanks CD. I'm getting lifted tomorrow, so that gives me some things to look at! ??
 
Remember to take lots of pictures when lifted! Nice to have in any case ;)

You'd be able to detect whether the shaft turning resistance is too much. On the hard, even with no water to lube the cutlass, my props turn by one hand, even by an elleven year old. Not free as an outboard, though.

For the sake of good order also check everything (esp. the prop) for damage as that indeed could cause vibration.

Next would be to check tightness of connections. Despite the prop nut being tight the prop itself might be loose on the key. If the nut is tightened properly the prop should sit firmly on the tapered shaft & key.

The noise when working the prop clock and anti clock wise: If not the prop/shaft itself then probably just gears in the gearbox having the play neccessary for them to work. If the gearbox is in neutral when you check the gears shouldn't move, though

As mentioned the gearbox to shaft bits need to be checked and re-tightened.
 
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I'd think that trying to identify the source of a tapping sound underwater is extremely difficult. I had a thing where the prop nut was tight because it was secured with the tab washer but the prop was sliding up and down the taper. I can't see a cutlass bearing causing a loss of speed but if there was enough friction on the shaft to slow the boat, wouldn't the shaft get extremely hot? Did you hear any unusual noise?
 
colhel said:
I'd think that trying to identify the source of a tapping sound underwater is extremely difficult. I had a thing where the prop nut was tight because it was secured with the tab washer but the prop was sliding up and down the taper. I can't see a cutlass bearing causing a loss of speed but if there was enough friction on the shaft to slow the boat, wouldn't the shaft get extremely hot? Did you hear any unusual noise?
Click to expand...
There was a bit of unusual metallic sounding vibration. This only happened for a second or two on 2/3 separate occasions. I'm hoping it was the prop anode rattling around! ?
 
ChromeDome said:
Actualy strange as it would possible only if the prop lost 'grip', which it would do if fouled (something tangled up) or lost firm connection to the shaft.
Click to expand...
There may well have been a bit of rope wrapped around and my cutter freed it. I'm hoping the vibration noise was my prop anode spinning on the retaining nut ??
 
Having re-read your post, I'd be looking at the split coupling. While it's still in the water, mark the shaft near the split coupling, put in gear and load up as much as possible and see if the mark is still in the same place relative to the split coupling
 
colhel said:
Having re-read your post, I'd be looking at the split coupling. While it's still in the water, mark the shaft near the split coupling, put in gear and load up as much as possible and see if the mark is still in the same place relative to the split coupling
Click to expand...
Ok will do, once I've googled what and where the slit coupling is!! ?
I guess it's a joint just after the gear box?
 
Yes. There'll be 4 or 6 bolts which when tightened will squeeze the clamp onto the shaft. These have to be really tight as all the power from the engine is transferred to the shaft via this clamp. It may be the noise you heard was from either something getting caught on the prop and the extra load caused the shaft to spin in the coupling, or the coupling being loose and it's just becoming apparent. Basically your wheel spinning, thus loss in speed.
 
ST840 said:
Would play in the cutlass bearing cause lack of speed when revs were ok?
Click to expand...
I don't think so but something round the prop or p bracket could. A bag would be temporary as would a rope if the cutter is effective. I once had an issue with the propshaft turning in the coupling under load. Mark the relative positions and run it even tied to the pontoon but work it a bit.
 
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