Prop

Post by **caseylynn** » Sat Aug 13, 2011 6:54 pm

What diameter and pitch prop are you guys using on a 36 with a 120 Lehman with 2 to 1 gear reduction. Mine is billowing black smoke at WOT only making 1900 to 1950 rpm's. My guess is the boat is overproped. Thanks

Post by **jleonard** » Sat Aug 13, 2011 7:46 pm

My 40 with 120 Lehman and a 2:1 gear ratio is using a 20 x 16 prop. I just get 2500 rpm. No smoke.
Jay

Post by **caseylynn** » Sun Aug 14, 2011 10:54 am

Thanks for the info J. What kind of rpm do you use for cruising? My 36 seems to work good around 1650 to 1700 rpm that gives me about 7 to 7.5 knts with no smoke! The smoke only appears when at WOT still only 7 to 7.5 knts. Thanks

Post by **jleonard** » Sun Aug 14, 2011 12:34 pm

I would suggest you calibrate your tachometer before you do anything else. 7.5 knots at 1650 seems fast to me like your tachs are off.
I cruise at 1750 and get 6.5 to 7 knots normally.

jcollins · Post by **jcollins** » Sun Aug 14, 2011 3:08 pm

caseylynn wrote:What diameter and pitch prop are you guys using on a 36 with a 120 Lehman with 2 to 1 gear reduction. Mine is billowing black smoke at WOT only making 1900 to 1950 rpm's. My guess is the boat is overproped. Thanks

I know nothing about your setup other than what I read on this forum. But, how long has this been going on? A new condition or just something you have ignored? When you say billowing I envision a black cloud chasing you down the river. Is that what you see? Could this be caused by something else?

John

Post by **psneeld** » Sun Aug 14, 2011 7:41 pm

agree with jleonard...at 1700 I get around 6.5 knots from my 40 albin

Post by **jleonard** » Mon Aug 15, 2011 8:35 am

When you say billowing I envision a black cloud chasing you down the river. Is that what you see? Could this be caused by something else?

Black smoke is incompletely burned fuel. Can be caused by either too much fuel (as in overpropping) or not enough air (as in clogged air filter). There are some other causes but usually one of these two are the fault.
(If it were a turbocharged engine there could be other issues but we are talking naturally aspirated here)

Post by **caseylynn** » Mon Aug 15, 2011 1:16 pm

The tach readings have been verified to be correct. The air filter and fuel filter are not restricted. J are you using a 3 0r 4 blade prop? Thanks.

Post by **jleonard** » Mon Aug 15, 2011 7:22 pm

caseylynn wrote:The tach readings have been verified to be correct. The air filter and fuel filter are not restricted. J are you using a 3 0r 4 blade prop? Thanks.

4 blade and a 2:1 BorgWarner gear (which I think is actually 1.91:1).

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