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Old 18-05-2017, 06:48   #1
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Prop Question

I recently purchased a Cooper Seabird 37 (1974, I think) with what I understand to be the original Perkins engine. There was no prop anywhere when I bought it so I have nothing to go on. This is going to be a live-aboard so I don't have any significant performance requirements, just something reliable and appropriate.

It isn't easy finding Owners Manuals or any detailed information about this particular boat. This is about all I've managed to find other than a few brief threads on here.

Thanks in advance for any information - I really appreciate it.

~jack
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Old 18-05-2017, 08:06   #2
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Re: Prop Question

Just about any prop shop can tell you what you will need. Plenty of used props out there that can be pitched to your boat.
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Old 18-05-2017, 10:02   #3
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Re: Prop Question

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Originally Posted by Jack Ware View Post
...I don't have any significant performance requirements...
Yes, you do. You can't just slap any prop on the boat and expect that you won't be damaging the engine. Your engine and transmission require a specific diameter and pitch to stay working properly.
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Old 18-05-2017, 10:32   #4
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Re: Prop Question

Welcome to the forum Jack.

As Guy has indicated, it is not a difficult calculation, you just need to Google the reference material. You could do this yourself, but wherever you buy the prop will do the maths for you.

These calcuations are only a starting point. In practice, the prop may be a little under or over pitched. If you get the prop shop to do the calculations they may be a little more inclined to adjust the pitch at a reasonable price if the estimations are incorrect.

As an alternative, many feathering props have adjustable pitch. You still need to have the basics such as diameter correct, but there is usually easy adjustment of pitch. Your sailing speed will benefit, but they are not cheap.
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Old 18-05-2017, 11:21   #5
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Re: Prop Question

If you go to the michiganwheel website they have a calculator for it. With the displacement, engine power, gear ratio etc. they can come up with good rough estimate. Go get a used prop that is close to the pitch they give you and go from there. That's what I did and got a prop for $200 and then repitched it for another $200 the new prop would have been closer to $700
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Old 19-05-2017, 06:06   #6
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Re: Prop Question

Greetings and welcome aboard the CF, Jack.
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Old 19-05-2017, 07:05   #7
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Re: Prop Question

The advice about prop calculators is spot on but the first things I would do would be to measure your arpeture (sp?) and shaft size. If the recommended prop wont fit in the opening with 15% clearance then you will need to go to a diameter that will, and figure the pitch for the smaller diameter. Also a 3 blade will absorb more HP for a given diameter than a 2 blade. Assuming you are on a budget, used gear shops have hundreds of props for sale at reasonable prices. Know your exact shaft diameter and if it is a metric or SAE taper so that you dont end up paying a machine shop to re-bore what you thought was going to be a bargain. Is your engine a left hand rotation or right hand? I am going through this right now and clearance is my biggest issue> Good Luck. ____Grant.
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