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View Poll Results: Locking Transmission
Yes, all the time 63 55.26%
No, I put it in forward 12 10.53%
No, I never do 24 21.05%
Huh??? Why???? 15 13.16%
Voters: 114. You may not vote on this poll

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  #71  
Old 06-22-2007
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DC generators

I've been looking into the possibilty of adding DC generators to my twin shafts for battery charging while under sail. There do seem to be a couple of products out there in the marketplace, but I haven't read of anyone evaluating or commenting on the feasability. I'd be interested to learn if 3 or 4 charging amps could be generated at say 6 knots with a 2 blade prop.

Rick in Florida
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  #72  
Old 06-22-2007
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velvet drive hydraulic transmission

Should I put a brake on the prop shaft or let it spin? I know in a car with a auto-tran it hurts the transmission.
Help! Don
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Old 06-22-2007
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I've got a Borg Warner, Velvet Drive transmission and the PO told me he always put the prop in reverse when sailing - so I followed suit.

However, I just did a quick online check with a certified marine mechanic's site and found conflicting information:

Quote:
1-1. Every Velvet Drive marine transmission is self-contained, having its own sump and hydraulic pump separate from the engine. The Rear driven pump affords assurance of positive lubrication.
Quote:
3-4. Freewheeling
It has been determined by tests and practical experience that all Velvet Drive marine transmissions can be free-wheeled without risking damage in sailing or trolling applications. Caution should be taken to be sure that proper oil level is maintained prior to freewheeling as well as normal running. Freewheeling one propeller of a twin engine boat at trolling speeds will not cause damage to the transmission connected to the freewheeling propeller.
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Last edited by TrueBlue; 06-22-2007 at 12:05 PM.
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  #74  
Old 10-21-2007
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Locking Shaft (or Not?) for a Max-Prop

Here is the Max-Prop Owner's Manual instruction:

PROPELLER USE The Max Prop works automatically. By putting the engine in gear the blades will engage in either forward or reverse. The best way to feather the propeller is;
• Power at 2 to 3 knots in forward.
• Kill the engine while still engaged in forward.
• When the engine has stopped, if the shaft is still spinning engage the transmission in reverse to stop the freewheeling.
You can check to see if the propeller is feathered or not by taking the engine out of gear. If the propeller is not feathered the shaft will freewheel like with a fixed blade propeller.
In that case start the engine again and repeat the three steps. If your propeller has been greased properly it will feather in a fraction of a second as soon as you stop the shaft from freewheeling. Once the prop is feathered, you can either leave the transmission in gear or out of gear, it does not matter. DO NOT kill the engine while in reverse. In this case the blades will be in the reverse position and will not feather. You can actually use this feature to drive a shaft alternator.
IMPORTANT: If the Max-Prop is installed on a vessel that can attain sailing speeds over 15 knots, it is MANDATORY to return the transmission to neutral while sailing. If the transmission remains engaged and the propeller were to open (from hitting an object or water flow) it may turn the engine, flooding it, resulting damage to the engine.
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Old 10-22-2007
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Jerry - Fluid dynamics are quite different between compressible (air) and non-compressible (water).
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Old 10-22-2007
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On the olde Volvo, I just put the gearbox into reverse. If not, you have to listen to a scuff-scuff-scuff sound as the prop spins and it will drive you round the bend. It would be a very good way of generating power though... at moderate speeds, there is some serious torque there but I would worry about wear, long term.

I have marked the shaft so that on a very long haul, we can align the two blade prop with the long keel to minimise drag.
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Old 10-22-2007
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You must determine weather your tranny is hydraulic or manual before deciding on the decision
Hydraulic transmissions will more than likely need some type of brake to stop rotation.

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Old 10-22-2007
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I can't add much about Marine props but I can shead some light on airplanes. I have an ATP and fly (have flown) a King Air 200 about 800 hours. I am a corporate pilot.

The King Air 200 has a Pratt & Whitney PT6-42 engine that DOES have a transmission (of sorts) I had a high pressure fuel pump fail in flight and I got a chip detector light which suggusted shutting down the left engine. Even fully feathered, the prop DID rotate (not a lot but it did spin) In the simulator we have to fly every year, the airplane will not fly unless the prop is feathered so there is some drag.

As far as the marine prop's go. in the 80's I used to crew a 39 Yankee and a 30 Tartan, both owners had painted a mark on the prop shaft indicating when the folder (remember 70-80s tech here) was in trail meaning both blades left and right to each other. Then we wrapped a rag around the shaft and put a pair of vice grips on the shaft to hold it.

In order to keep from making a vice grip size hole in the boat by starting it with the vice grips holding the shaft, we would put the ignition keys around the handle of the vice grips so you had to take the key OFF the vice grips to get the key back. I don't know if it made one bit of difference to our boat speed as the Tartan 30 was pretty slow (I did LOVE that boat though) The Yankee won a bunch of races but the guy sailing it was pretty sharp.

Great topic all!
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Old 10-22-2007
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OK, CD - since this is a poll and a fascinating thread. Yanmar 4JH-DTE; maxiprop. I put it in reverse while sailing and pull the throttle back. In an emergin-stroke, I start it in gear.

Have been thinking about a gori prop to reduce Maine Lobsterpot tangle around extended (but feathered) blades, but decided the bloody cold water untangling bath saves what Sailing Dog calls "boat dollars."
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Old 10-23-2007
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Volvo cone clutched gearbox with fixed pitch 3 blade prop -

We always sail with it locked in reverse if only to stop the noise (sailing is supposed to quiet else should get a power boat ).

Manual states leave in neutral if a fixed pitch prop and lock in reverse if not - commissioning engineer said to disregard and lock, and if jambs just start the engine (we find that on the occasional time it does jamb that just a quick crank of the engine with no fuel so doesn't even start always frees the box).

Prop designer states that our prop has least drag when locked and I guess he knows - it is a high aspect ratio 3 bladed (long skinny blades) prop optimised for sailboats.

As an aside, the experiments conducted in the MIT lab did not test locked props at all even though there are continual claims that they did (a simple read of the paper confirms that ). The experimentors did make a couple of very shallow assumptions, probably unsound in my opinion, and from those stated that freewheeling props had least drag - at best it was an unsound generalisation.

But in the end the silence of a locked prop wins out for us and all else is irrelevant.

I would have thought that if drag was important enough for someone to fuss over whether locked or not is least drag, they wouldn't have a fixed pitch prop would they ?
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