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post #1 of 9 Old 05-04-2013 Thread Starter
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Reusing a prop

I'm salvaging various parts off my I-28 that didn't survive Sandy. I had purchased a three-blade prop years ago and it served me well. I'm thinking of swapping out the two-blade on the new-to-me I-30 Bahama. Is there any downside to doing so? Should I expect better propulsion if I do?
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post #2 of 9 Old 05-04-2013
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Re: Reusing a prop

Is the old prop the proper pitch and diameter for your new boat's engine/transmission/displacement? Props are typically not interchangeable from one boat design to another.
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post #3 of 9 Old 05-05-2013 Thread Starter
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Re: Reusing a prop

The prop is an Indigo three blade design at 10" diameter and 7.7" pitch. Is there any reference or source that could tell me if it would hurt or help? The I-28 had a 30 HP Atomic 4. This vessel has a Yanmar 2GMF that is rated at 15 HP.
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post #4 of 9 Old 05-05-2013
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Re: Reusing a prop

I believe that one of the advantages of a 3 blade prop like the Indigo prop is that you will have much better control in reverse as well as possibly better propulsion in forward.
As to whether the Indigo prop is a good match for the Yanmar 2GMF I'm not entirely certain. I'd guess that it is in the ballpark but you might call the fellow at Indigo who sells that prop and ask him what he thinks.
I say that it is in the ballpark because while the Atomic 4 is rated to 30 HP the assumption is that most of the time this engine is delivering in the range of 15 - 25 HP.
It might help to figure out what size/pitch 2 blade prop is on your I-30 now. This is usually stamped into the bronze body of the prop.
Of course you could just swap the props and see how it performs and switch back to the 2 blade if needed.

We use a 2 blade prop on our Tartan 27' with our Atomic 4. The 2 blade prop can be oriented to "hide" behind the dead wood of the keel thus reducing drag - which you cannot do with a 3 blade prop.

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post #5 of 9 Old 05-05-2013 Thread Starter
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Reversing--something I have to do every time I return to port-- was one of the reasons I bought it for the I-28. I'll give the folks at Indigo a call and see what they advise.
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Re: Reusing a prop

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Reversing--something I have to do every time I return to port-- was one of the reasons I bought it for the I-28. I'll give the folks at Indigo a call and see what they advise.
I think that's the right thing to do. They should be able to tell you whether it needs to be re-pitched (assuming it can be).

T. P. Donnelly
S/V Tranquility Base
1984 Islander 30 Bahama
Pasadena, MD
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post #7 of 9 Old 05-06-2013 Thread Starter
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Re: Reusing a prop

Just an FYI. I called Indigo and the gentleman said that the I-30 has a reducing gear for the diesel engine and it wouldn't turn the prop fast enough. He said he had worked with another customer who wanted to do the same a while back and even changed the prop pitch, but it didn't help. In the spirit of sour grapes, it was going to be too hard to remove the old prop anyway... ;-)
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Re: Reusing a prop

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Just an FYI. I called Indigo and the gentleman said that the I-30 has a reducing gear for the diesel engine and it wouldn't turn the prop fast enough. He said he had worked with another customer who wanted to do the same a while back and even changed the prop pitch, but it didn't help. In the spirit of sour grapes, it was going to be too hard to remove the old prop anyway... ;-)
Good point! Whenever you provide the prop's setup info to determine pitch, you must also provide the transmission's gear ratio. Islander used several different ones with the Yanmar, so you can't just assume the most common one. You can find it on the plate on transmission case, which is readable from the access port in the quarter berth of the I30B.

T. P. Donnelly
S/V Tranquility Base
1984 Islander 30 Bahama
Pasadena, MD
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Re: Reusing a prop

Critical point. With the reducing gear you need to swing a bigger prop.

Sour grapes can make good wine!

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