Prop Shaft Lock

[Petronella]

Mehalah has a lovely shiny red new Beta engine but also apparently a lovely shiny new HYDRAULIC gear box. This appears to mean that putting her into reverse when sailing will not stop the prop from spinning. It makes a noisy whine and there is some vibration. I don't like that so I want to install a simple prop shaft brake.

The solution needs to be mechanical and able to be applied quickly and easily. I guess it needs to a) stop the prop's initial rotation and b) be designed so that an unforseen start of the engine won't destroy anything.

Could I stop it rotating by grabbing it by hand (sounds dangerous) and then stick a chopstick through the universal joint wedged against the hull that would snap if the engine was started up?!

Googling suggests various solutions from a molegrip to a purpose made, expensive gizmo.

What does the panel think?

The solution adopted will be named after its suggestor as in "I'll just go and engage the Simon".

 

[Deleted member 36384]

I have a Borgwarner hydraulic gear box and the propellor shaft spins. To counter this I use mole grips over an old leather belt. I have never tried to stop the shaft by hand. I loop the belt around the shaft, double up, insert the mole grips and then clamp shut. The good thing is that if I forget to remove the engine doesn't even notice and mole grips flop off. The leather obviously stops the mole grips damaging the shaft. The leather does get messed up and it needs to be replaced from time to time, but no big deal, and not often. It is dead easy, no cost and no hassle.

Engaging 'BlowingOldBoots' is a bit of a mouth full, should this solution be adopted. I got the idea on here, so engage the 'PBO' lock may be better. or BOB, as I am usually referred to in polite company.

Good luck.

 

[RobbieW]

I have an Autoprop combined with a hydraulic box that needs to be stopped to align the blades. I have a piece of string though one the floor 'joists' which hooks onto one of the coupling bolts, starting the engine (provenly )snaps the string if not removed. Stopping the shaft spinning fast can be a bitch, as can removing the string when under way at speed. Luffing up and slowing down makes both operations simple.

 

[Tim Good]

Or get a folding / feathering prop.

 

[langstonelayabout]

Or get a folding / feathering prop.

+1

My fitting a Flexofold prop to a previous boat was a revelation. Sailing became faster and motoring (both ahead and astern) better too. Forget the shaft lock.

 

[Spuddy]

I was going to suggest adapting bicycle brake unit but string outclassed that entirely

 

[duncan99210]

+1

My fitting a Flexofold prop to a previous boat was a revelation. Sailing became faster and motoring (both ahead and astern) better too. Forget the shaft lock.

The problem with either a folding or a feathering prop is that you need to stop the shaft turning to get them to fold/feather. That’s why you have to engage a gear on a mechanical box and use a shaft brake of some sort on a hydraulic box.

 

[DownWest]

If the shaft coupling is smooth, how about a leather strap that grips that, perhaps adapted from a filter wrench? Coupling is a big bigger diam that the shaft, so better leverage.

 

[Tradewinds]

I'm not a fan of grabbing the shaft to try and stop it - especially if wearing a leather glove for protection. Somehow, the little finger of the glove got caught in the turning coupling and I honestly thought I'd torn my finger off.

Out of interest, this is C&N's drawing for the shaft brake on a Nic39. I think it's a motorcycle unit? Doesn't look too complicated (but what do I know )

 

[langstonelayabout]

The problem with either a folding or a feathering prop is that you need to stop the shaft turning to get them to fold/feather. That’s why you have to engage a gear on a mechanical box and use a shaft brake of some sort on a hydraulic box.

The instructions that arrived with my Flexofold said that when you finish motoring, click the gear into reverse for a second at tickover revs: this will fold the blades backwards most of the way and water flow will do the rest.

This is how it worked on my boat (albeit without a hydraulic box) so I can't help thinking that it shouldn't be too bad from there.

I've also been the proud owner of a Gori folding propeller. Lovely and shiny and didn't need the reverse gear engaging for a moment to fold it.

By hand, neither the Gori or Flexofold needed any effort to fold their blades. Still, you pays your money, etc...

 

[captainboo]

The problem with either a folding or a feathering prop is that you need to stop the shaft turning to get them to fold/feather. That’s why you have to engage a gear on a mechanical box and use a shaft brake of some sort on a hydraulic box.

I have a feathering prop with a hydraulic gearbox and no shaft brake. You just switch off the engine in fwd gear and the prop stops quicker than the hydraulic pressure can dissipate so the propellor feathers without any problem. This is the recommended method by the prop manufacturer.

 

[Tim Good]

I have a feathering prop with a hydraulic gearbox and no shaft brake. You just switch off the engine in fwd gear and the prop stops quicker than the hydraulic pressure can dissipate so the propellor feathers without any problem. This is the recommended method by the prop manufacturer.

That's right and that's how we all do it with hydraulic gearboxes. Common practice and that's what Varifprop says.

Turn engine off in gear and it folds instantly before the hydraulic pressure is lost.

 

[Petronella]

Oops. Previous message deleted in error.

Thanks for all your comments. It looks as though it's a choice between leather or string or else splashing out on a feathering prop. Just returned from an expensive day at the boat show so the final decision will be deferred for a bit but I now have all the information I need.

Thanks again.

J

 

[rogerthebodger]

Oops. Previous message deleted in error.

Thanks for all your comments. It looks as though it's a choice between leather or string or else splashing out on a feathering prop. Just returned from an expensive day at the boat show so the final decision will be deferred for a bit but I now have all the information I need.

Thanks again.

J

Could something like this be adapted.

https://www.banggood.com/BIKIGHT-16...MIxtfoq5vJ3QIV6rDtCh00FA4LEAQYAiABEgIc4PD_BwE

 

[pcatterall]

Considered a ( cheaper) bike disk brake but didn't want to disconnect prop again to fit. used a cantilever bike brake but it and the cable went rusty! I can stop the prop by hand and will look for a useful point/nut to try the string solution! I Or leather belt with mole grips sounds my style as well!

 

[Petronella]

It's been a few months since I first asked this question and during that time I've tried a few things.

Mark 1: Two semi circles of stainless clamped to the shaft coupling with an electronic Quashai handbrake caliper. It might well have worked but was too complicated and we feared for a situation where it 'failed on'. (PIC 1).

Mark 2: An anode bolted to the prop shaft in a more accessible position with one of those large wide band jubilee clip type things on a bracket that could be meachanically tightened around the anode. Too fiddly.

Mark 3: A piece of household string looped around the threads of one of the shaft coupling bolts and led to a substantial engine bracket. Result? Success up to 4.8 knots. Then the string snapped!

Next I set up a little 'string lab' to identify a cord stronger than the string but weaker than a piece of 2mm rope. (PIC 2).

Mark 4: Potentially the final solution. A piece of thin orange crabbing line of which I have many metres. I've been surprised at just how much torque is generated by the rotating prop and I wanted a string that would snap if we needed to start the engine suddenly or simply forgot but would remain intact otherwise up to say 10 knots. Hopefully I now have that. We will have a routine whereby another piece of crabbing line is hung next to the ignition key whenever the 'brake' is applied. (PIC 3).

So, it's thanks to RobbieW for his suggestion, forever remembered when we say "Shall I connect the Robbie?" or "Is the Robbie still connected?"

Thanks guys.

J

 

[RobbieW]

...
So, it's thanks to RobbieW for his suggestion, forever remembered when we say "Shall I connect the Robbie?" or "Is the Robbie still connected?"
...

Fame at last ! I'm deeply honoured :encouragement: thank you