engine problems 4LHA-stzp

[lionelz]

well had a good say out on the solent today except for one thing, lack of SOG, engine was running fine with no abnormal noises and would rev upto 3200-3400, however the Sog was awful, between 9knts and 15 mainly it did have the odd spurt of speed going upto 22 knts but then back down but just seemed to lack power. The fuel consumption was awful too done about 200 ltrs from gosport to the needles when I would of thought a 100 would have been closer. 2 days before we had taken it out and was getting 27 knts out of it, in the same condidtions. Now Im not a techno wizard so any help in simple terms, I did when I when I bought the boat have diesel bug, it has a full service this was about 6 weeks ago, I have used it a bit since any help would be much appreciated. one frustrated person

 

[n.herring]

Dirty bottom

 

[lionelz]

I would not think so as its only been in water 2 weeks. I drained the fuel filter today and took it out and it appeared to work fine i then managed to hit something in the water luckily its being lifted so i can have a look at it

 

[n.herring]

If you are hitting the revs it will be nothing to do with the engine or fuel, if you had bent a prop you would have vibration, be interesting to know what you find when lifted

 

[[2068]]

Could be a rope or piece of net around the prop.

 

[salar]

I have the same engine in a Harley 25 which is semi displacement. With the leg fully trimmed down she flies up to 29 knots. Trim it up a bit and I can't get more than 13 knots which is a dramatic difference. What sort of boat and hull do you have, and is it inboard or outdrive?

 

[lionelz]

I have the same engine in a Harley 25 which is semi displacement. With the leg fully trimmed down she flies up to 29 knots. Trim it up a bit and I can't get more than 13 knots which is a dramatic difference. What sort of boat and hull do you have, and is it inboard or outdrive?

Its and inbourd on with a leg on it, I have a sports cuiser 30ft planning, I tried all the trimming of the engine and the trim tabs, nothing. As I said out today and was fine had 27 knts until I hit something under the water, just ope there is no extra damage. any suggestions would be much appreciated.

 

[lionelz]

If you are hitting the revs it will be nothing to do with the engine or fuel, if you had bent a prop you would have vibration, be interesting to know what you find when lifted

thanks for this will bear in mind if happens again. The temps were all fine to, just so frustrating, but I suppose thats boating for you

 

[salar]

Most likely the rubber bush in the prop hub has sheared. It is designed to absorb shock due to hitting things and can come unbonded by itself. It means the engine revs but the prop slips on its boss. I had that go on a Mercruiser leg, I could do five knots but no more even though the engine was revving. However I would have thought it would have completely sheared by now rather than slipping.

 

[beejay190]

Most likely the rubber bush in the prop hub has sheared. It is designed to absorb shock due to hitting things and can come unbonded by itself. It means the engine revs but the prop slips on its boss. I had that go on a Mercruiser leg, I could do five knots but no more even though the engine was revving. However I would have thought it would have completely sheared by now rather than slipping.

Yes, that is what happened to me when I ran aground in Poole Harbour many years ago - when the tide came back I had plenty of revs but little drive. A cheap fix.

 

[lionelz]

Thanks guys, I'm down the boat tomorrow, and will check, I take it I just turn the prob by hand see what happens and see if it all moves together, if not what am I looking for?

 

[salar]

The prop is manufactured with a metal hub that fits over the drive splines, with a rubber tube bonded round that, and the blade unit slid over and bonded to the rubber. If the blades rotate at a different rate to the drive shaft and hub, the rubber bond is slipping. If it is not slipping much you may have to put it in gear and give it a good push, or it may be quite loose.