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Old 23-08-2016, 05:01   #1
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Free prop or locked prop?

on the Jeanneau SO43DS i have Yanmar 4jh3-te motor (75HP) with KM4A clutch/gear , should i sail with free spinning prop, or shaft locked?
it is the original non folding prop.

thanks
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Old 23-08-2016, 05:10   #2
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Re: free prop or locked prop?

Neither -- you should buy a folding or feathering prop. Best investment you can make if you ever sail at all.

While you're waiting for the new feathering or folding prop to arrive, however -- let the fixed prop spin. But ONLY IF this is permitted by the gearbox manufacturer. Many marine gearboxes don't allow this. You'll have to read your manual to know whether yours is one of those.
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Old 23-08-2016, 05:34   #3
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Re: free prop or locked prop?

not mentioned/cant find any info in the manual
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Old 23-08-2016, 05:42   #4
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Re: free prop or locked prop?

Yanmar and the gearbox manufacturer (Kazkaki) recommend keeping the shifter in neutral when under sail. If left in gear, it can cause glazing of the cone which will lead to the transmission slipping.
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Old 23-08-2016, 08:11   #5
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Re: free prop or locked prop?

With regards to their sail drives, Yanmar even goes as for as to say that if you do not leave it in neutral during sailing, you run the risk of voiding the warranty.
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Old 23-08-2016, 08:12   #6
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Re: free prop or locked prop?

man, has this topic not been kicked around??? there is a consensus and a quick search will show easily that the consensus is that there is no consensus and that's why folding props were invented.
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Old 23-08-2016, 08:20   #7
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Re: free prop or locked prop?

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Originally Posted by jrbogie View Post
man, has this topic not been kicked around??? there is a consensus and a quick search will show easily that the consensus is that there is no consensus and that's why folding props were invented.
Actually it has been definitely proven in several tests that a spinning prop produces much less resistance than a locked one.

So I think there is a consensus -- lock it only if your transmission won't allow you to leave it spinning (some hydraulic ones for example). The idea that a locked prop produces less resistance is an urban myth which has been definitely busted.

But ultimately, yes, of course, folding or feathering is the only really decent solution, if you actually sail.
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Old 23-08-2016, 08:26   #8
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Re: free prop or locked prop?

Ignoring the transmission issue, Maine Sail did some tests that pretty well prove that a free wheeling boat prop creates less drag than a stopped prop.

The exact opposite is true for an aircraft propeller. When you turn off an airplane engine, you want to stop the prop so you can glide farther.
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Old 23-08-2016, 08:27   #9
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Re: free prop or locked prop?

got it, i will leave it to spin, so now comes another smart question, is there a generator you can attach to the shaft that while spinning it will charge your batteries?
i know there are hydro generators, but the common sense is to make use of this spinning shaft energy to do it,

comments please?
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Old 23-08-2016, 08:36   #10
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Re: free prop or locked prop?

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Originally Posted by Izikalvo View Post
got it, i will leave it to spin, so now comes another smart question, is there a generator you can attach to the shaft that while spinning it will charge your batteries?
i know there are hydro generators, but the common sense is to make use of this spinning shaft energy to do it,

comments please?
I don't know of a kit to do that but I bet it can be done.
That brings up another issue. I would bet that by putting a load on the spinning shaft and prop, you'll increase drag. No such thing as free energy. Might be a good trade off. I guess you could call that indirect wind energy.
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Old 23-08-2016, 08:41   #11
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Re: free prop or locked prop?

Yours will spin that fast, enough to power a generator? Mine would not, and I guess I have a weird one too as the manual for my boat said lock it by placing the transmission in reverse, but I have an older boat with clutches as opposed to cones and maybe that is the difference.
I now have a feathering prop and although my boat is no racer, it gave me an extra half a kt or maybe even a kt in higher winds, conversely to what you hear it made little to no difference in light winds as at low hull speeds drag is low, it makes more and more difference the faster you go, something like drag going up inversely with speed maybe?
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Old 23-08-2016, 08:47   #12
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Re: free prop or locked prop?

My boat is equipped with VP D1 20B (18hp) and S130 SailDrive. The manual says the gear has to bee in neutral when sailing. Its a little noisy and unfortunately there is no PTO on the gear for attaching a generator.

My next shopping will be a folding or feathering prop!
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Old 23-08-2016, 08:48   #13
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Re: free prop or locked prop?

Quote:
Originally Posted by Kokanee View Post
Yanmar and the gearbox manufacturer (Kazkaki) recommend keeping the shifter in neutral when under sail. If left in gear, it can cause glazing of the cone which will lead to the transmission slipping.
Not only that but if left in gear and you are in some large wave conditions--18+ feet or more--it might start turning over the engine. Did with ours. Fixed three bladed prop. Not good. So let it free wheel. Or buy a locking break to stop it, or just buy a maxi prop.
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Old 23-08-2016, 08:50   #14
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Re: free prop or locked prop?

Quote:
Originally Posted by Izikalvo View Post
got it, i will leave it to spin, so now comes another smart question, is there a generator you can attach to the shaft that while spinning it will charge your batteries?
i know there are hydro generators, but the common sense is to make use of this spinning shaft energy to do it,

comments please?
Sure. Here's one example: LIFE: Part 2: Prop-Shaft Driven Alternator. Google is your friend here.


But it will increase the drag even more. So it will really be like sailing with the brakes on.
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Old 23-08-2016, 08:52   #15
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Re: free prop or locked prop?

it is already proven on my boat that when the shaft is locked in reverse i am loosing half a knot, just wanted to be sure no harm is done to the gear letting it spin,
regarding the generator there must be something some company made, of course there is no free energy but if you need to charge your batteries any way while sailing under sails it is better to do it with an already spinning shaft than using wind or hydro generator or start the engine for alternator power.
i can go on mentioning tilting magnets with no friction in the kill that need the ballast anyway but this should be discussed in another thread.

shaft generator anybody?
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