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Old 22-09-2008, 12:33   #1
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volvo md7a, low power

can anyone help, my leisure 27 yacht seems to have no power under engine, gradualy getting worse untill this weekend it cannot stem a two knot tide. the engine revs hard with no load , slightly less under load, the engine emits virtually no smoke , temp normal, at the beginning of the season fitted replacement prop, identified correct code numbers etc, attempted inspection under water, some barnicles on prop and hull but can this really reduce my cruising speed to under two knots from 6. checked throttle linkages, correct travel noted, no tacho so do not know if i am achieving full rpm.
can anyone help or give me some items to check
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Old 22-09-2008, 16:13   #2
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Barnacles can take a lot of power...

I put a Yanmar 7hp in the 32' Ferro that I built too long ago.

I didn't antifoul the prop on ideas that were current at the time and after about 6 months I found that the boat was not going anywhere.

When I checked the prop was covered in growth.

With a small engine and a small prop the % loss is going to be higher.

Nowdays I make sure the prop is well antifouled.
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Old 22-09-2008, 16:55   #3
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Bottom dirty
Prop dirty
Prop fouled


Our boat will go from 6 knots motoring to 2 knots motoring when the prop and bottom are fouled.
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Old 22-09-2008, 21:23   #4
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While going ahead......shift to neutral then put it in reverse.

If the boat keeps moving forward it is the prop. (Fouled)
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Old 14-11-2008, 15:26   #5
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I experienced exactly the same problem with the same engine. Turned out that the wire for the stop handle had developed a slight bend, causing it to not push the stop lever on the diesel pump all the way forward.

My remedy was simply to use a shock cord around the lever and forward around one of the fuel pipes to act as a spring to force the stop lever into position. It was meant as a temporary measure, but it's still there 1 1/2 years later and works well. Only takes a bit more force to stop the engine.
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Old 14-11-2008, 16:20   #6
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how are the fuel filters?
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