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Old 03-03-2015, 06:03   #1
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Prop Brake

I have a 30 ton yacht with a Borg-Warner Velvet Drive gearbox which has a hydraulic clutch. As such .. the propeller turns when the boat is sailing.

I'm looking for some ideas for the construction of a (cheap!) brake. Previously a split drum was bolted around the shaft and a fixed belt pulled up onto the drum, but the belts keep breaking and getting chewed up because the shaft isn't horizontal so the angle of force required for braking and for lifting the belt into position are different. Even a steel belted radial got chewed to shreds (as well as damaging the drum).

I'm thinking of a motorcycle disc brake, but it seems difficult to mount the calipers or find suitable disc. The disc part would have to be cut in half and bolted back together. I don't think there's enough space for a car sized disc.

How have others solved this problem?
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Old 03-03-2015, 06:11   #2
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Re: Prop Brake

One popular solution is a feathering Maxprop or similar.
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Old 03-03-2015, 14:10   #3
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Re: Prop Brake

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One popular solution is a feathering Maxprop or similar.
Sure but that's not suitable for me. i have a fixed prop. I need a "cheap" solution, replacing a brand new prop isn't cheap, even if there was one available for my size boat (which there wasn't when I investigated it).

I specifically chose a non-feathering prop anyhow, I don't like the complication, maintenance burden, unreliability, and stress factors involved with feathering designs. Great for race boats .. but I'm a cruiser.
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Old 03-03-2015, 14:48   #4
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Re: Prop Brake

Why do you want to stop it from spinning would be my first question. Most transmissions that require a locked prop have a provision for this, and if your transmission doesn't require a fixed prop there is less drag allowing it to rotate.
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Old 03-03-2015, 14:59   #5
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Re: Prop Brake

I will try to explain my setup.

A machined disc bolts onto the drive shaft flange. How you set up the disc will depend on your flange, if you have a flexible coupling, and a cottonreel spacer between shaft and gearbox, and so forth.

Braking is provided by a mechanical motorcycle disc brake caliper mounted to the boat, positioned appropriately over the disc. A flexible cable runs from the caliper to the underside of the cockpit sole, where it is joined to a ss rod which slides in a ss tube fixed to the underside of the cockpit sole. the rod and tube pass through the cockpit sole. A knurled knob screws onto the top of the rod in the cockpit, pulling it up tight, engaging the brake, and also sealing the tube against water in the cockpit. Engaging/disengaging the brake is done by screwing/unscrewing the knob in the cockpit. The knob is located at the base of the steering pedestal, away from toes.

Everything is custom made, and somewhat expensive. I had to replace the disc some years back (warped), and I think the machine shop charged $600. That was in a very expensive mining boom area.

Lee
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Old 03-03-2015, 15:03   #6
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Re: Prop Brake

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Originally Posted by Stumble View Post
Why do you want to stop it from spinning would be my first question. Most transmissions that require a locked prop have a provision for this, and if your transmission doesn't require a fixed prop there is less drag allowing it to rotate.
Agree. My 24 tonne boat has BorgWarner and with the low revs the gearbox doesn't heat up so no probs. More drag if brake is on.

Is it too noisy?
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Old 03-03-2015, 15:07   #7
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Re: Prop Brake

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Why do you want to stop it from spinning would be my first question. Most transmissions that require a locked prop have a provision for this, and if your transmission doesn't require a fixed prop there is less drag allowing it to rotate.
It's noisy, and it wears the bearings and probably the clutch too. The gearbox actually heats up quite a bit. My "transmission" is a standard motor vehicle transmission. So is my motor, with mods to the cooling system. (Nissan Patrol motor actually).

I don't care about drag. Cruising yacht. Not interested in performance much. Very interested in maintenance costs from excess wear. I like sleeping too, which is impossible with the shaft turning under sail since my bed is right on top of it. The noise is also a safety issue, a lot of sailing depends on hearing, especially at night.
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Old 03-03-2015, 15:19   #8
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Re: Prop Brake

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Originally Posted by banjoship View Post
I will try to explain my setup.

A machined disc bolts onto the drive shaft flange. How you set up the disc will depend on your flange, if you have a flexible coupling, and a cottonreel spacer between shaft and gearbox, and so forth.
Rigid coupling.

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Braking is provided by a mechanical motorcycle disc brake caliper mounted to the boat, positioned appropriately over the disc.
Can I ask, how big is your boat, and what size motorcycle the brake was designed for? And also how did you organise the caliper mounting?

Your design is roughly what I plan, however I don't want to decouple the shaft from the gearbox so I plan to cut the disc in half and bolt it back together. [I'm not even sure how to get the shaft end of the coupling off the shaft ..]

Since the brake does minimal work actually stopping the turning shaft that should be OK I guess. Mostly the brake is locking the shaft so the load is static.

Quote:
Everything is custom made, and somewhat expensive. I had to replace the disc some years back (warped), and I think the machine shop charged $600. That was in a very expensive mining boom area.

Lee
I'm in an even more expensive major city where a day on the hard would cost more than that ;(
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Old 03-03-2015, 16:10   #9
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Re: Prop Brake

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Originally Posted by yttrill View Post
Rigid coupling.



Can I ask, how big is your boat, and what size motorcycle the brake was designed for? And also how did you organise the caliper mounting?

Your design is roughly what I plan, however I don't want to decouple the shaft from the gearbox so I plan to cut the disc in half and bolt it back together. [I'm not even sure how to get the shaft end of the coupling off the shaft ..]

Since the brake does minimal work actually stopping the turning shaft that should be OK I guess. Mostly the brake is locking the shaft so the load is static.



I'm in an even more expensive major city where a day on the hard would cost more than that ;(

My boat is a 42' Swanson, about 20 tonne fully loaded, 75hp engine, BW velvet drive, built 1981. The original builder (Shaun Arbor) put in the brake system.

The brake caliper? Who knows what it is from, I don't think it is important, as long as it is a reasonable size. You may have trouble finding a mechanical caliper nowdays.

The caliper is bolted to a steel strut spanning the engine room. This strut supports other gear, exhaust lift box, etc.. A plate off the strut sets the right angle to mount the caliper over the disc.

A split disc seems like trouble to me. there are only a few bolts holding the flange to the gearbox, no trouble to fit remove a disc. And at some stage somebody is going to engage the engine with the brake locked, generating a lot of heat. I am guessing that that is how the PO warped the disc I had to replace.

Lee
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Old 03-03-2015, 16:51   #10
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Re: Prop Brake

Quote:
Originally Posted by yttrill View Post
I have a 30 ton yacht with a Borg-Warner Velvet Drive gearbox which has a hydraulic clutch. As such .. the propeller turns when the boat is sailing.

I'm looking for some ideas for the construction of a (cheap!) brake. Previously a split drum was bolted around the shaft and a fixed belt pulled up onto the drum, but the belts keep breaking and getting chewed up because the shaft isn't horizontal so the angle of force required for braking and for lifting the belt into position are different. Even a steel belted radial got chewed to shreds (as well as damaging the drum).........
Could you adjust the angle of the belt to match the angle of the shaft? Would that solve your problem?
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Old 03-03-2015, 17:03   #11
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Re: Prop Brake

Take a look at a company called Shaftlok. Frankly I find shaft breaks unjustified, but if you want one i have heard ( though have no experience with) good things about them.

I would still highly recommend looking at a feathering prop instead. I appreciate you are looking for a no maintenance solution, but there isn't one. Locking the prop introduces a lot of load on the drive system as well, all that torque has to go somewhere. Maintenance on most feathering props is pretty minimal reaching none. At least no more than squirting greese into the hub whenever you pull the boat for a bottom job.
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Old 03-03-2015, 17:10   #12
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Re: Prop Brake

Mount an alternator and enjoy the spin
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Old 03-03-2015, 22:59   #13
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Re: Prop Brake

The noise of a spinning prop drives me crazy. Yanmar says prop should spin not locked in position by putting in reverse. Tried to live with the spinning for the first few days out of SF on the way to Hawaii had to stuff it in reverse before I went bonkers. Have just put in reverse ever since figuring there is a transmission rebuild in my future. Their used to be a commercially trans brake some years back. Think they no longer in business.

On previous boat used a pair of vice grips on the shaft. Can't get at the shaft on the current to use them. Vice grips worked fine even when i forgot to remove them. They'd pop I ff the shaft as soon as the transmission was put in gear. No fun digging them out of the bilge after, however.
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Old 03-03-2015, 23:16   #14
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Re: Prop Brake

Vise grips with a lanyard! or a pipe wrench.
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Old 03-03-2015, 23:32   #15
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Re: Prop Brake

I used the REALLY CHEAP prop brake. In the 80s I bought a steel boat. My first passage was to Bermuda, and the shaft spinning almost made me crazy. I could tell every wave we surfed down. In Bermuda, I bought a hook with a hole in the end to bolt it to the coupling. Removed one bolt from the coupling and installed the hook. I attached a piece of 1/8 inch line to a hard point, and made a loop in the end to go around the hook, and as soon as I left harbor I would hook the shaft and have silence. If I forgot to put the engine in reverse for a second or two when I started it, the only thing was a few cents worth of line was broken. The down sides to this are, you have to be able to reach the coupling, you must hook it before boat is moving fast enough to start the shaft turning or turn into the wind for a few moments to slow down and stop the turning. The big upside is the off-watch gets much better sleep. The boat was powered with an automotive diesel (Mercedes) with a Velvet Drive. As a side note, many shaft brakes are connected to the engine oil pressure, so that as soon as the oil pressure comes up, the brake goes off. That is much more reliable than remembering to undo a mechanical brake. Just my 2 cents worth. _____Grant.
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