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Old 29-11-2013, 06:46   #16
jjt
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Re: Prop spinning under sail ???

You can slow down the rotation using a pulley and an alternator with an electric clutch.
This way won't silence completelly the noise but at least will get some extra amps while going fast forward (under engine and/or under sail)

You can search the web for this implementation, I'm sure saw a few cases in the past.
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Old 29-11-2013, 07:35   #17
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Re: Prop spinning under sail ???

This is worth a read on the merits of locked or spinning:

http://www.plaisance-pratique.com/IM..._sdarticle.pdf

The summary states:

The experimental results confirm that a locked propeller
produces greater drag than does a freewheeling screw (up
to 100% more drag was observed, this being at higher
speeds). Furthermore, for the freewheeling case, the
magnitude of the hydrodynamic resistance is significantly
affected by the amount of frictional torque on the shaft,
low torque being accompanied by low drag.


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Old 29-11-2013, 08:07   #18
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Re: Prop spinning under sail ???

Quote:
Originally Posted by Pete7 View Post
This is worth a read on the merits of locked or spinning:

http://www.plaisance-pratique.com/IM..._sdarticle.pdf

The summary states:

The experimental results confirm that a locked propeller
produces greater drag than does a freewheeling screw (up
to 100% more drag was observed, this being at higher
speeds). Furthermore, for the freewheeling case, the
magnitude of the hydrodynamic resistance is significantly
affected by the amount of frictional torque on the shaft,
low torque being accompanied by low drag.


Thanks Pete,
Nice to have some hard data to back this up.
In my mind I thought the same, but had some doubt to my logic due to many people telling me otherwise.

I'll continue to let the old Volvo gearbox freewheel. The cone clutch is disengaged when free wheeling, so no wear. Also very quiet, I don't even notice it.
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Old 29-11-2013, 09:34   #19
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Re: Prop Spinning under Sail?

you can buy an aftermarket shaft lock if your concerned about it.The velvet drive in my boat has been in service since 1976 with the prop spinning under sail. Dont sweat it. I like the sound of the gearbox spinnning, it means Im doing above 4kts. Id take this trans above any other given the performance of and longevity of the one I have. Same goes with the perkins, how many yanmars will be around after 37 years of service and over 10k hrs and still go oil change to oil change without having to add oil?
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Old 29-11-2013, 10:16   #20
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Re: Prop Spinning under Sail?

When I still had my day job all our ships were twin screw.... if we were in no hurry to get to where we were going we would run on one engine. The engineers would always let the idle prop freewheel as that offered the least resistance.

Another small point...something dragged through the water will always seek the path of least resistance... if 'not spinning' offered the least resistance then Walker logs and towed generators simply wouldn't work.
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Old 29-11-2013, 10:24   #21
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Re: Prop Spinning under Sail?

More data for the OP... The 4-108/Velvet drive combo in the Morgan is as others observations... Starts freewheeling around 4 kts regardless of either gear engagement... I actually HAVE a shaft brake, but don't use it.... It works fine, I prefer to have the engine start in forward because that's the propulsion direction I would prefer in 95% of "Get the engine fired now" situations...

FYI-My shaft brake is a caliper and shaft mounted disk, cable operated with a lever...
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Old 29-11-2013, 23:14   #22
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Re: Prop Spinning under Sail?

The better shaft brakes are connected to the engines oil pressure. When you start the engine, the pressure comes up and releases the shaft. Very few people slam their engine into gear before the oil pressure comes up. My own cheepo solution to a banshee howling prop shaft in a steel boat was to put a SS loop (like a tack fitting for a small main sail) onto the coupling, and have a small line with a loop on the end that fit over the SS loop., I would put the engine in reverse for a second, and then into forward. If I forgot, it would just snap the line and no other problem. I did this in Bermuda, because I could not sleep through the ever changing howl of the prop shaft. It is cheep and works. ______Grant.
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Old 29-11-2013, 23:17   #23
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Re: Prop Spinning under Sail?

I should have said, I would put the engine in reverse for a second to release the shaft stop. Thinking and typing is tough. _____Grant.
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Old 30-11-2013, 09:24   #24
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Re: Prop Spinning under Sail?

With my luck, if I ever put a pipe wrench on my prop shaft it would lock in place and the boat would do a 360.
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Old 12-12-2013, 14:33   #25
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Quote:
Originally Posted by ranchhand View Post
With my luck, if I ever put a pipe wrench on my prop shaft it would lock in place and the boat would do a 360.
Haha good one
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Old 12-12-2013, 15:30   #26
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Re: Prop spinning under sail ???

Quote:
Originally Posted by neilpride View Post
wear in the stuffing box in the long run is another story
How much water needs to go through to prevent wear?
Couldn't a small electric inline pump (like a car fuel pump) feed water in to lubricate the bearings?

Quote:
Originally Posted by Pete7 View Post
The experimental results confirm that a locked propeller
produces greater drag than does a freewheeling screw (up
to 100% more drag was observed, this being at higher
speeds)
Seems quite obvious doesn't it, like dragging a bucket behind the boat.
I am surprised its even being argued.
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Old 12-12-2013, 15:40   #27
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Re: Prop Spinning under Sail?

If you have a Yanmar, you should not lock the prop using the transmission.

"Yanmar requires that if sailing with the engine OFF (not running) the transmission shifter must be in the neutral position or internal damage to the gear or sail-drive will result. This damage will not be covered by Yanmar’s Limited Warranty."

See: http://www.shaftlok.com/YANMAR_MSA08...al+Sailing.pdf
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Old 12-12-2013, 16:25   #28
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As I understand it Maine Sail did some testing some time ago and found a pretty huge difference between locked and free wheeling, locked having somewhere close to 300% more drag than free wheeling
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Old 13-12-2013, 10:13   #29
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Re: Prop Spinning under Sail?

I have a round vice grip pliers with inner tube rubber for a shaft lock. If you worry about starting the motor with lock on use the starter key trick( key attached to pliers when on shaft) If you don't have a start key throw a breaker or pull a fuse so starting the motor becomes a two part drill to remind you of lock. This is same technique I use with raw water intakes which get turned off to make sure I don't run motor dry.
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Old 13-12-2013, 14:31   #30
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Re: Prop Spinning under Sail?

yeah, locking the prop always struck me as being as sensible as dragging a bucket, glad to see a bit of research to support.
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