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post #1 of 10 Old 10-15-2011 Thread Starter
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prop madness

I have a bristol 29.9 with a yanmar 2QM15. It is turning a 3 blade 14-10 prop. Don't seem to have much thrust. Just scrapped the prop not too bad had a couple of june bug size barnicals and a mess of lady bug size. Any suggestions for more thrust? When @ 2500 rpm lucky to make 4.6...

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post #2 of 10 Old 10-15-2011
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Originally Posted by Maverick1958 View Post
I have a bristol 29.9 with a yanmar 2QM15. It is turning a 3 blade 14-10 prop. Don't seem to have much thrust. Just scrapped the prop not too bad had a couple of june bug size barnicals and a mess of lady bug size. Any suggestions for more thrust? When @ 2500 rpm lucky to make 4.6...
It doesn't take a lot of fouling to blow the efficiency of a prop all to hell. That said, 4.6 kts doesn't sound terrible (but, not great either) for that size engine in that size boat at that rpm.

Was the speed you report @2500 rpm before or after you cleaned the prop? What is the speed @3000 rpm (redline)? How clean is the hull?

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post #3 of 10 Old 10-16-2011
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Quote:
Originally Posted by Maverick1958 View Post
I have a bristol 29.9 with a yanmar 2QM15. It is turning a 3 blade 14-10 prop. Don't seem to have much thrust. Just scrapped the prop not too bad had a couple of june bug size barnicals and a mess of lady bug size. Any suggestions for more thrust? When @ 2500 rpm lucky to make 4.6...
Did you scrap the prop or scrape it?

Bristol 31.1, San Francisco Bay
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post #4 of 10 Old 10-16-2011
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Change the prop with a more pitched one.
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post #5 of 10 Old 10-16-2011
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I have a 2QM15 with a two blade prop (don't know the pitch) on Far Cry a fat 31' cruiser. When there is any, and I mean any, crud on the prop, performance suffers badly. A slightly dirty prop combined with a dirty bottom, forget motoring anywhere at a decent pace. In flat calm water with a perfectly clean prop and bottom 6.0kts is max speed. Typically I motor at around 5kts.

Having the barnacles you describe on my prop would easily knock me down a knot or two. It is amazing...
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post #6 of 10 Old 10-16-2011
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I use prop speed. This photo shows the prop after being in the water for 2 years and moved 3500nm.


Just out of the water and with the other side being water blasted. ='before' &


'after'


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Last edited by St Anna; 10-16-2011 at 06:04 PM.
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post #7 of 10 Old 10-17-2011
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As point of reference, my Islander 30 Mkii will do 6.4 knots with a 13X8 2 blade behind a Beta 14.

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post #8 of 10 Old 10-17-2011
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That sounds like a LOT of prop to me...
But i dont know your system.

Did the boat and prop work well once upon a time?
Or are you working this issue out for the first time?

gh
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post #9 of 10 Old 12-09-2011
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It's 2:21 so I'm not doing the math, but if you have the 2.2? to 1 I beleave the manual calls for a 280 mm pitch, the 2.8? is like 3?o mm I think someone took the two bladr pitch and went to a three blade.
It's in the service manual under I think it's set up, Prop
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post #10 of 10 Old 12-18-2011
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Red face

Is this a new problem to the boat? Was it OK last season?

If it is a new problem There are many things that can cause a diesel to run slower then slower:
Check the fuel filter. If you have a vacuum gage an increase in vacuum will tell you it's clogging up.
Check the feed line Diesel fuel breads algee, and Algee clogs things, I once saw an Island freport 41 with Algee in the vent line, caused a vacuum, the boat left the slip doing 5 knots, then 3 hours later came back at 2 knots
You can check for water topping the water seperators, But thatn shoud shut her down pritty quickley.
Put it in nuetral and turn the shaft coupler. the Stuffing box could be locking up.
Also look for an air ristriction. ( Not Likely)

If it's a new vessel or the was a prop change:

The Yanmar Service manual states:
gear ratio Blades size
2.14 3 360 x 250MM
2 380 x 230
2.83 3 blade 430 x 320 MM
2 460 x 280

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