Join Date: Mar 2007
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I donít know if this will help but I have fitted several Max Prop propellers (and are very satisfied with them including several customers), when they came down from the manufacturers they had a setting that they should be set for that vessel/engine and I have normally set them up at that, however most of them we have had to re-set them slightly one way or another.
In one instance we pitched the prop more and the boat gained about a knot extra speed, but the engine revs were down from 3400 flat out to 2800, the friend was very happy as he could now keep up with us!!, but the engineer who looked after the boat said it was overloaded, however its run like that for over 10 years without any problems.
On our boat, which is a similar size, engine is a ford 90bhp and we only get 2000 rpm at best however itís a much lower revving engine (max cont revs 2500) and at 2000 rpm we are getting 8.5 Knots.
When we first fitted the prop, on the settings from the manufacture we were getting 2300 rpm but only 7.5 Knots, we pitched the prop a degree more and gained the extra speed and less revs, we hardly ever run the engine over 1800 rpm and for more fuel economy (while the price is high) we have been running it 1500 rpm giving the said 7.5 Knots.
It sounds like an incorrect prop size, what it the ratio of the gearbox and what size prop do you have?
Also could it be a problem in the gearbox and as suggested by others a fuel starvation? How clean is the bottom/prop? I knew someone who had a shortage of power under load and go the fuel pump re-calibrated and all of a sudden regained the lost revs (I think it was about 5-600) it could be this that causing your problem.
Go to the boat manufacturers and see what prop should be on this set-up, or a well established prop manufacture should be able to give you a guide.
I hope this helps, sorry to go on a bit.
Please let us know how you get on