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Old 06-04-2014, 07:31   #1
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Help ,, I have two different props on my Lavezzi40

Wanting to paint the props correctly, I found out that I have different
props, one says 16x13L, the other 17x14L ????
That does mean they are different YES/NO ???
Does that cause problems YES/NO ???
And if I would have to buy one new one I might want to
buy folding props, does anybody with a Lavezzi know which
size is better
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Old 06-04-2014, 07:58   #2
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Re: Help ,, I have two different props on my Lavezzi40

Yes different

first number is the diameter in inches (25.4mm=1.0 inch)
second number is the non-slip forward motion for one revolution.

As the larger prop is also a greater pitch, it will effect a significantly greater load on the engine. For equal pitch, the power draw increases with the square of the average diameter more or less.

If the prop is not adequately matched (too big) to the motor capability AND the vessel drag and hull speed, the motor may be prevented form reaching its optimum design rpm and therefore power.

A good example for me was when we replaced the Merc 35 HP outboard on our small patio boat with a 4-stroke Nisan 35 HP. We expected the performance to be same/similar. The Merc 2-stroke had quick acceleration and good top speed. The new Nisan was a slug. I had the feeling it was over-torqued and went through a 2- step regression to shallower pitch. I believe steps were 17-3/4 14 9-3/4. If I compare the rpm-torque ratings of the two motors, the Merc is typically rated max HP at about twice the rpm of the Nisan. This might not normally matter so on a lightly loaded, overpowered boat but on a displacement patio hull with relatively high drag it makes a big difference.

BTW. How do you find time to worry abut the props with one of 'those' on the transom? We always assumed 'they' came with the boat.
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Old 06-04-2014, 08:09   #3
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Re: Help ,, I have two different props on my Lavezzi40

it might be that the larger prop is the correct pitch,when using 2 engines,and the smaller one under pitched to provide more torque when running on a single engine.

i would also guess the engine with the smaller prop,might have a big alternator as well,also requiring horsepower that would otherwise be going to the prop,so as not to overload the engine.
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Old 06-04-2014, 09:35   #4
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Re: Help ,, I have two different props on my Lavezzi40

I drove a twin screw that had two sizes of props , it had two different sized engines and the props were sized accordingly . Oil field crew boat !
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Old 06-04-2014, 10:42   #5
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Re: Help ,, I have two different props on my Lavezzi40

Quote:
Originally Posted by atoll View Post
it might be that the larger prop is the correct pitch,when using 2 engines,and the smaller one under pitched to provide more torque when running on a single engine.

i would also guess the engine with the smaller prop,might have a big alternator as well,also requiring horsepower that would otherwise be going to the prop,so as not to overload the engine.
That would explain some , but NO, simiiar alternator, apparently
the Yanmar do not allow space for a bigger one,
also I have seen that maybe one time in the past one of the
saildrives have been changed, but in that case they would have installed
these different props,
It could also have been lost at one time, one of the bolts holding
the cone is not metric !!!!! repaired somewhere maybe ?
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Old 06-04-2014, 11:06   #6
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Re: Help ,, I have two different props on my Lavezzi40

Quote:
Originally Posted by atoll View Post
it might be that the larger prop is the correct pitch,when using 2 engines,and the smaller one under pitched to provide more torque when running on a single engine.

i would also guess the engine with the smaller prop,might have a big alternator as well,also requiring horsepower that would otherwise be going to the prop,so as not to overload the engine.
Good point Atoll. I always figured twins would be made identical at least to minimize spare parts.
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Old 06-04-2014, 11:43   #7
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Re: Help ,, I have two different props on my Lavezzi40

You didn't mention what engine you have, assuming it's the 3YM30, the 16x13 would probably be more correct than the 17". I've only seen the 17" on the 40hp engine.
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Old 06-04-2014, 11:53   #8
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Re: Help ,, I have two different props on my Lavezzi40

Are they the same model of saildrive? If one was changed for a different model, that one may have a different gear ratio.

For folding props, I believe the Volvo 17x11 was used on that boat.

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Old 06-04-2014, 23:49   #9
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Re: Help ,, I have two different props on my Lavezzi40

Quote:
Originally Posted by colemj View Post
Are they the same model of saildrive? If one was changed for a different model, that one may have a different gear ratio.

For folding props, I believe the Volvo 17x11 was used on that boat.

Mark
It is the 3YM30, both sides,
There is a definite color difference between both saildrives!
one is blue the other grey, how do I find out they are different,?
the parts in the engine locker are the same ???
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