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post #11 of 19 Old 10-27-2008
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borg warner gear shaft lock

in 1983 i installed a system i had designed on a velvet drive to lock the unit to keep the prop shaft from turning. i called borg warner & an engineer said it would be OK as long as the oil pressure in the reverse clutch was above 100 lbs. i removed a plug near the top rear of the transmission to reroute the oil to an aeroquip hose to a valve in the chart room above the gear. i removed the front gear housing & tapped the oil passage from the rear for a pipe plug. with the plug installed i put the housing back on & removed the pipe plug from the housing where the vertical drilling brings oil to the reverse clutch. i hooked up an aeroquip line to this and this went up to a tee with a 200 lb gauge on it. this was connected to the valve. to lock the gear the engine was idling & put in reverse. then the ball valve was closed holding the oil pressure in the reverse clutch. we kept an eye on the gauge and after a number of hours the pressure would be down & we would open the valve. the hoses slowed the reverse operation somewhat. we used this setup for six years until the boat got caught in the ice and sank between greenland & iceland in 1989
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post #12 of 19 Old 10-27-2008
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Thanks Captain Bill - that's an interesting solution. Sorry to hear of her loss. I dont have the expertise to rig something like that and after looking at prices for feathering props probably wont go that route either. Right now im thinking small wooden dowel in the coupler that would be enough to keep it from turning under sail and weak enough to break if accidentally left in when engine was engaged. Not ideal but i don't have room to grab the prop shaft anywhere with a brake (cant even change packing without pulling the prop shaft out of the coupler).
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post #13 of 19 Old 10-28-2008
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To reduce the drag of your fixed prop, stop it from turning. It may seem counter-intuative, but it is true that a stationary propeller has less drag than a spinning one while under sail. Not to mention the un-necessary wear on cutlass bearings, thrust bearings and all the other seals and goodies hiding there in the dark.
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post #14 of 19 Old 10-28-2008
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Talking shaft lock

an update on what i do now to lock the shaft. the vessel i have now is a nimble 30 express sloop with a yanmar 2GM20F engine with kanzaki gear. i just put it in reverse to lock the shaft. i installed a perfect pitch 15 x 11 two blade prop & i don't think i have a lot of drag with the shaft locked. i get 6.9 kn. at 3600 engine RPM. that is 1374 shaft RPM with 2.62 gear ratio. i cruise at 2250 eng RPM @ 5.35 kn.
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post #15 of 19 Old 11-08-2008
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Quote:
Originally Posted by Capnblu View Post
To reduce the drag of your fixed prop, stop it from turning. It may seem counter-intuative, but it is true that a stationary propeller has less drag than a spinning one while under sail. Not to mention the un-necessary wear on cutlass bearings, thrust bearings and all the other seals and goodies hiding there in the dark.
I have finally found an authoritative paper based on actual experiments. See:
http://strathprints.strath.ac.uk/567...rag_Jan_08.pdf

Their conclusion is that the stopped prop has a higher drag than the freewheeling prop!
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post #16 of 19 Old 11-08-2008
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Nice find GC!! I don't think there can be any arguing with that data!

No longer posting. Reach me by PM!
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post #17 of 19 Old 11-08-2008
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In the interest of completeness, the citation for the published paper is:
Ocean Engineering
Vol. 35, No. 1, Jan 2008, pp 28-40
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post #18 of 19 Old 04-22-2009
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Prop brake

I have a PRM 500, and just called the HQ in UK. According to their engineers there is "absolutely no risk from letting the shaft freewheel". Putting a folding prop on will significantly reduce this motion, but not eliminate. I have talked to others who are fitting a hydraulic brake on the shaft...essentially like a car disc brake that is released by the engine powering up the gear box. hope that helps

Ron
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post #19 of 19 Old 04-22-2009
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I think the link is:
http://strathprints.strath.ac.uk/567...ints005670.pdf
cheers

"The sail, the play of its pulse so like our own lives: so thin and yet so full of life, so noiseless when it labours hardest, so noisy and impatient when least effective". -- Henry David Thoreau
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