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Old 05-30-2007, 03:54 PM   #1
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This is a question often asked here over the years. On my travels around the Net I came across this very useful website covering the topic.

"So we have engines and to transfer the power to the water efficiently, we have propellers. There is the old adage "a sailor only needs a small engine to get out of the marina into the wind and sail." Yah sure! And another is "the choice is the two-blade propeller that can be hidden behind the dead wood to reduce drag while sailing." Another yah sure!"

From: http://www.westbynorth.com/Choosing.aspx

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Old 05-30-2007, 04:32 PM   #2
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Hi Lighthouse

I have just had a new engine put into our boat a Yanmar 3YM30 consequently we had to have a new shaft which was smaller than than the old one consequently the old 3 bladed fixed prop wouldnt fit.

One dilemma we had with the fixed one is that whilst sailing do you leave the engine in gear ( some engines have actually started this way) or in neutral ( This could cause excessive wear on the cutlass bearing plus the noise of it going round)

We had a look round and decided that the best option was Bruntons Autoprop although expensive it is a lovely piece of engineering. Its to good to put in the water and get wet

As our boat is out of the water at the moment I have it in the garage. (Daren't leave it on the boat)

If you havent seen one I can take a piccy of it for you.

I cannot fault Bruntons at all. They required quite a lot of information about the boat age, model no,engine type, shaft angle etc. Then they wanted 2 weeks to assemble it. Apparently everyboat is different and they dont have any on the shelf

Another advantage is that if you should dink a blade it is quite a simple proceedure to change 1 blade and not the whole prop.

Hope this helps

Steve
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Old 05-30-2007, 04:39 PM   #3
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I don't know the Bruntons Autoprop - a pic would be great.

If you go to the "Propeller Recommendation" page at the above link you will see all the information (of the boat and engine) required in order to select the correct prop.
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Old 05-30-2007, 05:34 PM   #4
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Hi.

Hope these are OK

Steve
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Old 05-30-2007, 06:06 PM   #5
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Very interesting - thank you.

P.S. I had to resize your pics - you had a total of nearly 5Mb loaded up there - bandwidth killer.
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Old 05-30-2007, 07:51 PM   #6
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Also THE Treatise by David Gerr "The Propeller Handbook" a must on any List

of essential reading for the cruising yachtie.

Richard
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Old 05-30-2007, 08:06 PM   #7
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As I do with my batteries, I take an entirely different tack to my reasoning. I assume that I'm going to need to replace my prop (and batteries) at some point or another during a long period at sea. As such, I try my best to keep it simple and a two bladed prop works just fine for me. In addition, for a full keel boat like mine, I would argue that it is more efficient and less harmonic than a three bladed piece of engineering artwork.

Simple calculator for determining prop size based on HP & boat.

http://boatdiesel.com/
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Old 05-30-2007, 08:23 PM   #8
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Quote:
Originally Posted by Trim50 View Post
I assume that I'm going to need to replace my prop (and batteries) at some point or another during a long period at sea.
Our Maxprop still looked almost new after five years of cruising in the tropics. I did clean it regularly.
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Old 05-30-2007, 08:35 PM   #9
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Do you keep a second Maxprop as back-up in case you damage or spin the first? How much did the first one cost?

Everyone has different philosophies, mine is "Simple & Redundant".
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Old 05-30-2007, 09:38 PM   #10
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I have a standard fixed, three blade prop. The original fixed, two blade remains in the engine room ready to act as a spare. I understand the desire for folding props, but I am not sure that reduced drag is so important. I wonder if two weeks of marine build up on the hull would overcome the drag 'savings' of a folding prop. Also, in the grand scheme of things, I think wear on bearings is more of a theoretical than a practical problem when it is reduced to a per-year deterioration factor.

The noise of the shaft spinning can be a bother when trying to get to sleep, especially when one's boat is climbing, then falling away from crests (whirrrrrrrrrrrr-whir-errr-errr-errr-errr-whirrrrrrrrrr), but if it bothered me enough, I guess I could always install a shaft brake.

Thanks for the pointer to Boatdiesel.com Trim. Good site! I have just ordered Compton's Troubleshooting Marine Diesels.

Cheers

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Old 05-30-2007, 09:49 PM   #11
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Quote:
Originally Posted by Trim50 View Post
less harmonic than a three bladed piece of engineering artwork.

http://boatdiesel.com/
When I re-read my post, it sounded like I was bashing the Maxprop and I'm not. I think it is a beautiful work of engineering. The word "piece" was not entended to imply POS

I have a friend with a Maxprop on a Peterson 44 and he complained about how it works in reverse. Has anyone had the same experience?
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Old 05-30-2007, 09:53 PM   #12
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Quote:
he complained about how it works in reverse
"Crawls" like crazy.
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Old 05-30-2007, 09:58 PM   #13
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That is what he said. I never see him backing into his slip as a result.
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