Locking The Shaft

[Goldie]

I'm shortly to race on a boat with a Volvo 2002 or 2003 series engine and the owner has asked me how we can lock the shaft so that the prop doesn't free wheel and that the prop remains behind the deadwood. Apparently, putting the engine into gear (either way) doesn't work. Any ideas greatly appreciated (before I resort to a socking great pair of mole grips and some string).

Many thanks in anticipation.

 

[simonfraser]

how are you going to decide it's behind the deadwood ?

 

[eyehavit]

So is he saying with the engine OFF and transmission 'IN GEAR' the prop still turns. ????

 

[Bilgediver]

The volvo 2003 engine if fitted with the volvo gearbox locks by selecting astern. If you select ahead then it will of course free wheel.

Sometimes after some brisk sailing with the gearbox locked you might find it difficult initially to select neutral. DO NOT FORCE THE SELECTOR.... slow down under sail and restart in gear after which you should be able to select neutral.

You will have to mark the shaft so you know where the prop blades are and then turn the engine by hand after locking the shaft.


John

 

[Goldie]

That's the easy bit - I align the prop when I pop down to scrub the bottom and he marks the shaft inboard. Then when we stop the engine, we align the shaft by hand.

 

[Goldie]

That's what he tells me /forums/images/graemlins/confused.gif

 

[Goldie]

That's exactly what I'd expect - the only way will be to see for myself. Thanks.

 

[Anonymous]

[ QUOTE ]
I'm shortly to race on a boat with a Volvo 2002 or 2003 series engine and the owner has asked me how we can lock the shaft so that the prop doesn't free wheel

[/ QUOTE ]Locking the prop will slow you down unless it is a feathering prop?

 

[vyv_cox]

Halyard sell a shaft brake. I know nothing about it and have never seen one but it might be worth investigating.

 

[macd]

Not so. It may seem counter-intuitive but tests have shown the reverse.

 

[fireball]

[ QUOTE ]
Locking the prop will slow you down unless it is a feathering prop?

[/ QUOTE ]
Even behind the turbulant area of the "deadwood" .... ? Have you got a scientific test to prove that?! /forums/images/graemlins/tongue.gif

 

[steve_cronin]

Absolutely....

That is why a helicopter with a failed engine tries to windmill down because, like a falling sycamore seed, it offers greater resistance to the air when the blades are rotating. If the blades couldn't turn they would just be dragged through the air and the aircraft would drop like a stone.

Steve Cronin

Personally, just for one race I would use the molegrips but with leather pads to avoid shaft damage.

 

[FAITIRA]

I always lock the shaft for less drag.

 

[jollyjacktar]

Oh no!!! Here we go again , the old Hardy a /forums/images/graemlins/laugh.gifnnual of the non rotating prop being more/less drag.

 

[Anonymous]

Re: Locking the shaft

[ QUOTE ]
That is why a helicopter with a failed engine tries to windmill down because, like a falling sycamore seed, it offers greater resistance to the air when the blades are rotating. If the blades couldn't turn they would just be dragged through the air and the aircraft would drop like a stone.

[/ QUOTE ] No. The rotors need to be spinning for gyroscopic and lateral stability plus the inertia from the spinning rotor is sufficient to arrest the fall by increasing the pitch just before touch down.

It has nothing to do with sycamore trees or air resistance, it has to do with trying to keep the aircraft in a 'flying machine' mode and not a 'brick' mode.

 

[Chris_Robb]

No - he is saying that with Volvo "Crappy" gear box, if you engage reverse gear to stop the prop turning, it is absolutley imposible to get out of gear again, without startung the engine in reverse! Actually there is nothing fatal to the box by starting it in reverse, but engineers do say that volvo do not advise this.

To match up the prop to the dead wood the shaft would have to be marked on the inside, hopefully before the boat is in in water - but Goldies is already in so.... How you manage to engage the gear at the right moment though...

I have the same problem.

 

[Chris_Robb]

Re: Locking the shaft

Lemain - you could start a rival thread to the great Anchor choice one! perhaps LJ will join in.!

 

[Anonymous]

Re: Locking the shaft

/forums/images/graemlins/smile.gif This one comes up at least twice a year. Maybe it depends on the boat but with my Nauticat I lose a good knot when I put the engine in gear, so I don't do that.

Mind you, previously I believed that it was the right thing to do and I did not like the sound of the prop going round...and thinking of gearbox wear. Also, intuitively it seemed 'right' to stop the prop for some of the reasons already given in this thread. However, every time I put it in gear, she lost a knot. Pretty persuasive stuff, and I don't need text books to tell me that it is the case.....on my boat. Maybe not others?

As for locking the prop, I had the problem that it would not come out of gear when engaged under way and I had a nasty shock when for the first time I wanted the engine on approach to Le Harvre, crossing the shipping channel /forums/images/graemlins/shocked.gif and nothing happened when I tried to engage the starter. I headed up and took all way off but still it was locked. So I dug around for a small piece of wire and shorted out the gearbox interlock. Now I find that that all you need to do is give a quick blip - without starting the engine - and quickly pop the gearbox out of gear.

 

[cliffordpope]

I'd be interested to see the line of reasoning.
If you connected a generator to the rotating shaft you could extract a small amount of energy. As you increased the load on the generator you could extract more energy. However if you were too greedy you would merely suceed in stopping the shaft, in which case you would get no energy out at all.
So there would be an optimum speed of rotation for extracting the maximum amount of work out of the rotating prop. This energy would have to have come from somewhere, presumably from slowing the boat.
So the minimum amount of retardation on the boat would occure when the amount of energy extraction was least, which would seem to suggest that the prop should either be locked, or else allowed to rotate perfectly freely. This would never in fact be achieved, because of friction drag in the bearings and gearbox. Hence presumably the argument that locking the prop is the preferable option?

 

[vyv_cox]

Re: Locking the shaft

If I leave my gearbox in neutral after turning off the engine, my Autoprop does not feather but continues to rotate. With a Yanmar box it's no use putting it in forward as the shaft will continue to rotate, but reverse stops it. The prop then feathers but moving the lever back to neutral is difficult or even impossible. So I sail and restart the engine with the gearbox in reverse.

The answer might be to stop the shaft manually but this requires me to move the spinnaker, cockpit tent frame, two folding bicycles, two rucsacks, berth cushions, saloon berth infill and bunk boards first. /forums/images/graemlins/grin.gif