Problems getting on the plane - fletcher gts

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Mk2zetec

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Hi all
I've had a fletcher with 3.0l mercruiser/alpha 1 for a few months and whilst it was never going to be a rocket ship the performance was adequate.
The last few times out I've noticed it's a lot slower to spin up when the throttle is opened and to get up on the plane. This has been accompanied by a much louder exhaust. Investigation reveals that the exhaust bellows has come away at the transom end so I assume this has something to do with it. Is it the fact that the bellows allows the release of exhaust gas through the drive unit which allows the prop to spin up faster?
WOT IS 4600 giving at about 28 knots (with a 14.5 x 19 prop) from the gps whereas it was previously hitting over 30
Or is it something else? I noticed it was running on last time out but seems better using v-power fuel (google advice!) - potentially timing out?
Many thanks for any comments
Rich
 
You really need fix the bellows issue and then work from there.

It could be exhaust causing cavitation. It could be that that engine needs a different back pressure etc but correct the known Fault first.
 
Bouba said:
I think the bellows are the number one reason for sinking in dock
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Not exhaust bellows.

I don't think the bellows are your problem. Almost certainly either fouling to prop, hull or both, or fuel supply problem.
 
CLB said:
Not exhaust bellows.

I don't think the bellows are your problem. Almost certainly either fouling to prop, hull or both, or fuel supply problem.
Click to expand...
Yes, sorry, my bad. Speed reading error :ambivalence:
 
I have the same boat and engine and my exhaust bellows are off also. It is nothing to do with that. It will be growth on the hull. Prop and leg.

Last year I started the season at 30 Knots and ended it with 17 Knts because of growth, Clean in this year was back up to 30 knots. I am now at about 24 knts. Don't worry about the exhaust bellows most of these GTS's do that

Also have you added any weight to the boat. Also a 2 knot reduction is very little I am sorry to have to tell you

Dennis
Proud Owner of 6 Fletchers
 
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I would agree with jrudge, first fix the obvious problem then look for other things. Then a plus one with Dennis.
Your engine's exhaust goes through transom shield then through the exhaust bellows and down to the propeller. Depending upon which propeller you have, will then decide upon whether it uses Mercruisers PVS (Performance Vent System). If you have an ordinary Aluminium propeller, you wont have PVS unless it is a custom build. If on the other hand you have something like a Laser 11 propeller, for example, it will have holes which vent exhaust gases onto the propeller blades, this in turn helps spin the engine up without baulking, to it's best power band, to give a greater hole shot (in theory). Once the boat starts moving the water flow restricts the gases flowing from the vent holes giving a grip to the propeller.
So when you say, she is not spinning up so quickly, the lack of exhaust through the system would account for poorer hole shot, "if" you have a propeller with PVS holes. Also if the exhaust bellows is off at the transom end, you will have a little drag from it, but not likely you will lose 2knts.
So there are 2 factors you have described, one your engine is not spinning up as well in order that you have a great hole shot and two, you have some drag of which you are losing 2knts. Drag will probably be as already mentioned, hull crud and the spinning up could be a factor of this or your PVS not working proficiently.
HTH. :)
 
Added exhaust gas ahead of the prop would surely result in more cavitation and the prop would slip/spin up more easily but not reach desired speed? If it's slow to spin up, then I'd say there's probably either fouling on the prop as mentioned above or something wrapped around it maybe? I assume there's no damage (niks, dents etc) to the prop as this would also affect performance...
 
Added exhaust gas ahead of the prop would surely result in more cavitation and the prop would slip/spin up more easily but not reach desired speed?
Click to expand...

I couldn't agree more Rob, but I'm not sure the distance between the transom shield outlet (where the exhaust bellows was off) to the prop would be enough, not to provide ventilation to the propeller and would it lower the atmospheric pressure to the back of the blades to produce cavitation, not sure it would?

Good points about prop damage or fouling.
 
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