Shaft lock mechanics...help plse.

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Sinbad1

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I wish to stop my shaft turning whilst sailing. I have a disc similar to a brake disc that has been specially made for my shaft. I now need a MECHANICAL mechanism that will activate a set of brake pads or similar. Does anyone have any ideas how to do this.

I have thought of a motorcycle type system as on motorbike front brakes.

I don't want a system that is activated/deactivated by gearbox pressure. This is on offer through Brunton Autoprops but I would prefer a simpler mechanic system.

Any ideas gratefully received.
 
Try Twyflex Ltd.
The Green,
Twickenham,
Middlesex/
TW8 5AQ
Tel 0181 894 1161 Fax 0181 894 6056

They used to supply simple disc brakes, some manually/cable operated. I used them several years ago and found them helpful, but haven't used them recently.

dickh
I'd rather be sailing...
 
If you have a decent scrappy nearby, have a look for an old Land Rover. The handbrakes work with a disc on the propshaft, mechanically operated with cables.
I am sure a mount could be fabricated for the slave unit. A simple hook-and-eye for the other end of the cable with a turnbuckle for adjustment could replace the handbrake lever.
Good luck.
 
I must admit on the few occassions I have got fed up with the noise of the shaft turning, I have stopped it by putting the engine into gear (reverse works best).

Could someone please tell me why this isn't an ok solution? Is there a risk of damaging something by doing this?

Thanks
Rob
 
GO-KARTS USED TO USE A CABLE OPERATED DISC BRAKE ON THE REAR (1") DRIVESHAFT.

Try a Go-Karting centre. Modern karts use hydraulics but we have an old TRAX kart with a cable operated disc brake which would suit you down to the ground.

Sorry I'd get lynched if I let you cannibalise it!

Steve Cronin
 
bike breakers, yamaha fs-1m-dx, or simmilar. front brake caliper... cable operated disc, pads cheap as chips. even tho' you won't ever wear them out. use the standard lever on a piece of handlebar set into a block of timber, make sure it's accessible as you may need engine quickly!

hold brake on with a simple clip or a spacer in between the lever and the bracket it's mounted to. this allows easy and quick release.

small amount of pissin' about but it'll work a treat. regards, steve.


interested in stuff that needs mendin'

http://homepage.ntlworld.com/s.amos/index.html
 
Re: Shaft lock mechanics...some thoughts

With most gearboxes when you select reverse it will efectively stop the shaft from rotating. This is what most people do and is very safe. I can only assume your gearbox does not do this (eg. hydraulic gear engagement)
If you fit a shaft brake have you thought of the risk of someone starting the engine and engaging gear with the brake on? Or, even, starting the engine with the lever in gear and the brake on? (very few boats have an interlock switch that prevents starting in gear).
Also, don't forget that with a conventional shaft (without a separate thrust bearing) the prop pushes the engine forward when motoring forward so ensure you have plenty of clearance on a disc-brake otherwise as you motor ahead with the brake off the disk will be pushed into the forward disc-pad.
 
Rob, my gearbox is hydraulic and loses pressure once engine off, so prop turns shaft whether in gear or not. Turning shaft throws open blades on Brunton prop Which slows boat) and wears cutlass bearings.
 
In one of the Hiscocks books, he said he always used to stop his engine in Ahead.

This, he says, was to have it all ready to start and in ahead in case of emergency.

So if it was good enough for Hiscocks, it is good enough for me. That's the way I stop my shaft from rotating while sailing - and I would start it in gear if need be. In fact I did last Sunday when the speed dropped to 2 knots and I wanted to get home sooner rather than later.

regards,
Philip
 
Quite often it is desirable to lock the shaft in a particular position, eg. vertical prop alignment behind the deadwood. Rather than having a complicated brake system, how about a hinged arm with a right angled bend which drops into a notch in your disc. A spring could keep it dis-engaged and a simple cable would engage it. That way it would be failsafe. Alternatively if you use a push/pull control cable, you could mount an over-centre spring which will keep it engaged or dis-engaged as you wish. Lining up the notch would occur naturally as the propshaft rotated slowly and any shock loads could be absorbed by mounting the arm and even the disc on rubber bushes. I like also the suggestion of the alarm to warn you that the lock is engaged.

Having stirred my thoughts by your posting, I might be tempted to try the solution for myself.
 
Few points:

1. If you have a disc - use it. Motorcycle calipers easy to fit - relatively corrosion resistant - easy to operate.

2. Don't like the sound of a "notch". Too much danger involved if it is left in position and someone puts her in gear!! (With a caliper all you will do is stall the engine or run hot on the brake.)

3. Can fit limit switch to caliper arm so that you have a light on when brake is engaged. If you are really turned on with electrics the limit switch could even be tied into the "Start" circuit to prevent starting when locked "on".

4. Why not just stick her in gear?

Best regards :o)

Ian D
 
Re: Shaft lock mechanics...some thoughts

All well and good however when i put mine into astern to stop the rotation no amount of subsequent swinging on the morse will get it back into neutral, hence i have to start the engine in reverse and i am not so sure that is a good thing.

When i have tried putting it ahead the rotation did not stop, so now i just listen to the rumble and use it to keep an eye (or ear) on whether the crew are maintaing speed if i take 10 minutes below.
 
Re: Shaft lock mechanics...some thoughts

Why is everyone so keen to stop the shaft turning? After all, there's virtually no load on it when it's "freewheeling". I would have thought it was positively desireable to keep things turning gently and the oil in the box splashing round! - It's never done my boat (a little 12hp engine) any harm

Anyway, assuming I've missed something, you could try a brake disc from a mountain bike - maybe that will be easy to actuate and should be a pretty simple mechanism?
 
Re: Shaft lock mechanics...some thoughts

reason for stopping the prop when sailing:

1) unneccesary wear on propshaft bearings

2) there is more drag from a rotating prop than from a stationary one
 
Re: more drag from a rotating prop when sailing

I can't prove it, but others have provided enough evidence to convince me. This topic has been aired in this forum several times before. The basic fluid-dynamic theory is that a rotating propeller presents a much larger disc area facing the oncoming water flow that a fixed propeller which only presents, say, 50% disc area (ie the area of the blades). The theory holds good for propellers in both water and air.
See http://142.26.194.131/aerodynamics1/Multi/Page2.html
On a prop driven aircraft it is standard procedure when an engine fails to either stop the prop rotating or, with a variable pitch prop to feather it, to ensure the maximum efficiency from the other engine, or maximum glide angle if no other engine.
 
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