# Prop shaft brake



## pullark (Jul 5, 2008)

Hi,
I have a PRM hydraulic gearbox in my boat. I have a three blade conventional prop. The prop/gearbox rotates as I sail along. It's been suggested to me this is not a good idea as it will cause wear to gearbox bearings. Should I instal a prop shaft brake to prevent wear on transmission? Will drag increase or decrease as a result? Any simple design ideas for a braking system appreciated.
Thanks
Kevin


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## canadianseamonkey (Sep 4, 2006)

Hi Kevin and welcome to Sailnet, I have the same tranny. It depends on how long you sail, I don't always lock mine , it won't heat up right away, but as a precaution a break is best. I looked at those breaks they sell and settled on a pipe wrench. It works just fine as long as you don't forget it when you start your engine. Many people I spoke with use this fix. Give it a try. Good luck.


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## RXBOT (Sep 7, 2007)

*Shaft brake*

I have very limited experience with hydraulic gearboxes but lots of experience with hydraulics and lots with mechanical gear reducers.I seriously doubt that while saiing the RPM of the prop would be fast enough to be of any concern. However if you engaged the drive with pipe wrench in place you may have a new thru hull opening plus severe trauma to other components.


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## pullark (Jul 5, 2008)

Guys, thanks for your thoughts. I agree the consequence of forgetting to remove the wrench on engine startup could be quite scary.
Cheers
Kevin


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## SEMIJim (Jun 9, 2007)

Our mower has hydraulic drives (two: one for each drive wheel). Neutral is simply no drive power. To actually get the two wheels to free-wheel, I have to flip a manual release on each drive. Then they don't drive anymore, either.

It's been years and years since I've owned a car with an automatic transmission, but I thought that, in anything but neutral, the drive train was not free to move.

How are these PRM hydraulic gearboxes different?

Jim


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## timebandit (Sep 18, 2002)

A simple brake can be made from 2 pieces of 2x4 with a a V cut into each and clamped to gether with carrage bolts with springs and wing nuts.

Just tighten the brake enuff to stop the shaft. 

If you start the motor it will allow the shaft to spin but if you run for to long the wood will start to over heat and let you know you forgot it.  

Rick


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## Ilenart (Jul 23, 2007)

*Some hydraulic drives are ok to freewheel*

Pullark,

some hydraulic drives are ok to freewheel. My boat has a Velvet Drive hydraulic marine transmissions from Borg Warner and it's been freewheeling all the time & the boat is almost 30 years old. You might want to do some research into your particular gearbox.

I previously found the following on another website.

A number of major gearbox manufacturers have dispelled an earlier unfounded fear of gearbox damage due to improper lubrication while freewheeling. However some gear box manufacturers do not advise leaving the prop to free wheel as this can cause mechanical problems within the box (overheating due to lack of lubrication).

Ie - From "Velvet-Drive":
It has been determined by tests and practical experience that all Velvet Drive marine transmissions call 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.
Extended periods of free-wheeling at high speeds may cause the transmission to overheat; therefore, it is recommended that transmission sump temperature be monitored and free-wheeling discontinued whenever 230 degrees F or 111 degrees C is reached.

Sailing with tansmission in N or R - Cruisers & Sailing Forums​
Ilenart


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## wesselouki (Oct 7, 2008)

I have the same issue and am considering a folding prop. Does anyone know if a feathering prop will fold while sailing without locking the prop shaft? This would eliminate the potential for the pipe wrench effect and solve the gearbox issue.
Mike


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## AllThumbs (Jul 12, 2008)

I dunno about the gearbox wear but the drag will be least with the prop locked


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## LittleWingCA (Jul 17, 2008)

Is there harm in just leaving it in gear when the engine is stopped? I don't know what engine manufacturer you have, but for my Yanmar, the manufacturer recommends putting the transmission in reverse after shutting down the engine to keep the prop from free spinning. They recommend reverse over forward.


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## captbillc (Jul 31, 2008)

*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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## wesselouki (Oct 7, 2008)

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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## Capnblu (Mar 17, 2006)

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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## captbillc (Jul 31, 2008)

*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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## gc1111 (May 13, 2004)

Capnblu said:


> 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/5670/01/MacKenzie_PM_Sailboat_Propeller_drag_Jan_08.pdf

Their conclusion is that the stopped prop has a higher drag than the freewheeling prop!


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## camaraderie (May 22, 2002)

Nice find GC!! I don't think there can be any arguing with that data!


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## gc1111 (May 13, 2004)

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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## TSOJOURNER (Dec 16, 1999)

*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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## GreatWhite (Jan 30, 2007)

I think the link is:
http://strathprints.strath.ac.uk/5670/1/strathprints005670.pdf
cheers


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