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Old 09-02-2016, 09:18 AM   #1
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4 blade vs 3 blade?

Hello
I have a new to me boat. She is a Hardin 42 Sedan trawler.
She comes with a 4 blade prop. I am new to trawlers having just left the sailing world after 23 years. So big props are new to me.
Caroline has a single screw. 125hp turbo John Deere.
Why 4 blade vs 3 blade? Does one give better fuel use.

Thanks Ed
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Old 09-02-2016, 09:45 AM   #2
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It's a question that gets debated here every so often. Probably more important on performance boats, planing hulls, push boats and tugs. Find what works for you with the least vibration and be happy. Find a good prop shop to work with. It's a black art that involves voodoo and sacrifices. Best to use a professional.

Ted
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Old 09-02-2016, 09:52 AM   #3
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With a new to you boat and absent any specific issues like vibration or failure to reach rated rpm, the prop would be the last thing I would worry about at this time. As sailboaters, we tend to think a lot about fuel efficiency. I still do, but eventually have learned that fuel cost is one of the smaller expenses of ownership for most of us slow boat folks.
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Old 09-02-2016, 10:27 AM   #4
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Go big or go home I say!!
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Old 09-02-2016, 10:38 AM   #5
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Blade area and propeller loading will dictate the number of blades.
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Old 09-02-2016, 12:58 PM   #6
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Not interested in changing the prop just working on learning.
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Old 09-02-2016, 02:54 PM   #7
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28 x 20 four blade pushes my 45,000 lbs. boat at 7 knots on 2 GPH. Probably not going to improve on that economy with anything you do to the prop.

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Ted
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Old 09-02-2016, 03:37 PM   #8
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Read da Book

I suggest buying Dave Gerr's 'Propeller Handbook'. It's the best $10 or so (@ Amazon) you'll ever spend. If you take the time to read carefully, estimate, if not known, your boat parameters, and go thru the formulas and charts, you'll have at least a good idea, and probably more than most folks, about propeller selection.

https://www.amazon.com/Propellar-Han...sap_bc?ie=UTF8
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