Folding Prop - Clonk when engaging forward gear

Houleaux

Houleaux

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I've just fitted a 2 blade Varifold folding prop.

The boat went back into the water today and I started her up and engaged forward and reverse with her on her berth to make sure everything was working ok.

I did this from tickover and, whilst reverse engaged quietly, there was quite a loud clonk each time I engaged forward. (The boat was being driven in both forward and reverse, so the blades were opening ok).

I realise that the blades will open faster when in forward gear and therefore hit the stops with more force, but is this clonk normal?

The prop is quite big - 17" x 14 - and the blades are therefore correspondingly heavy.

My first thought was that the engine, gearbox and shaft were all moving forward as the prop took up drive in forwarrd gear and that maybe I'd fitted my rope cutter (a Stripper) too near the P bracket so it was hammering into that, but on reflection I think that that would be more of a tap than a clonk. I can't detect any fore and aft movement of the shaft when the gears are engaged.

The clonk happens a short while after the shaft starts turning, so I don't think it can have anything to do with the gearbox.

I'll ring the manufacturers in the morning for advice, but I wondered if anyone could put my mind at rest in the interim?! I really don't want to have to have the boat lifted again.....

Thanks.
 
Houleaux said:
I've just fitted a 2 blade Varifold folding prop.

The boat went back into the water today and I started her up and engaged forward and reverse with her on her berth to make sure everything was working ok.

I did this from tickover and, whilst reverse engaged quietly, there was quite a loud clonk each time I engaged forward. (The boat was being driven in both forward and reverse, so the blades were opening ok).

I realise that the blades will open faster when in forward gear and therefore hit the stops with more force, but is this clonk normal?

The prop is quite big - 17" x 14 - and the blades are therefore correspondingly heavy.

My first thought was that the engine, gearbox and shaft were all moving forward as the prop took up drive in forwarrd gear and that maybe I'd fitted my rope cutter (a Stripper) too near the P bracket so it was hammering into that, but on reflection I think that that would be more of a tap than a clonk. I can't detect any fore and aft movement of the shaft when the gears are engaged.

The clonk happens a short while after the shaft starts turning, so I don't think it can have anything to do with the gearbox.

I'll ring the manufacturers in the morning for advice, but I wondered if anyone could put my mind at rest in the interim?! I really don't want to have to have the boat lifted again.....

Thanks.
Click to expand...

I have a MaxProp the clunk is quite normal
 
On all boats i have sailed with folding props there is a loud clonk as the prop unfolds. It happens a few seconds after engaging forward or reverse.
I think its normal
 
The blades don't even open in astern which is why folders are rubbish in astern, it's the shape of the folded blades that shifts the water :)
 
Ceirwan said:
The blades don't even open in astern which is why folders are rubbish in astern, it's the shape of the folded blades that shifts the water :)
Click to expand...

That is just not true of all folding props. I have just fitted a Flexofold and did comparative tests for bollard pull in both forward and reverse and stopping distance and it was virtually the same as the fixed 2 blade it replaced. The only difference is a slight delay at tickover going into reverse before the blades open and a quick bit of power deals with that.
 
The Volvo saildrive on my previous boat had a two-blade folding prop; standard, nothing fancy.

It worked as well as one could reasonably expect in reverse, probably close to a fixed 2 blade.

I can say from observation that the folding props to avoid are the ones where the blades aren't connected by toothed cog quadrants; excellent chance of getting one blade out, with interesting results and heavy vibration.
 
I suppose there must be some props that don't work in reverse - at least, there must have been some to engender the myth. My boat is small enough that there is no discernable thump on engagement and only a little delay in reverse. The original prop was a Darglow 14x11 and I'm now trying a Flexofold 14x9. I believe the reverse function is largely dependant on having sufficient mass at the blade tips for them to throw out on centripedal force. The technique is to give a blast in reverse to deploy the prop and then throttle back to the required thrust.

Rob.
 
I have a huge 2 bladed feathering prop and it makes a clunk as the blades swivel around and lock into place. I am gentle with it, and replaced the pins in the prop whilst the boat was out of the water this winter, but I have got used to the clunk and it hasn't fallen off yet, so....
 
rob2 said:
I suppose there must be some props that don't work in reverse - at least, there must have been some to engender the myth. My boat is small enough that there is no discernable thump on engagement and only a little delay in reverse. The original prop was a Darglow 14x11 and I'm now trying a Flexofold 14x9. I believe the reverse function is largely dependant on having sufficient mass at the blade tips for them to throw out on centripedal force. The technique is to give a blast in reverse to deploy the prop and then throttle back to the required thrust.

Rob.
Click to expand...

Mine - fitted to the boat when I bought her, so I don't know its pedigree - is certainly unreliable in reverse. When it works, it is fine. But once in a while it decides not to open in reverse. The only solution is to put her into forward, then rapidly back into reverse - which is a bit nerve-racking when coming on to the pontoon, and on one occasion, resulted in my colliding with the pontoon.
 
Houleaux said:
I've just fitted a 2 blade Varifold folding prop.

The boat went back into the water today and I started her up and engaged forward and reverse with her on her berth to make sure everything was working ok.

I did this from tickover and, whilst reverse engaged quietly, there was quite a loud clonk each time I engaged forward. (The boat was being driven in both forward and reverse, so the blades were opening ok).

I realise that the blades will open faster when in forward gear and therefore hit the stops with more force, but is this clonk normal?

.
Click to expand...

Perfectly normal. The prop will never open fully in reverse so you dont get a clonk. It will quickly open fully against the stops in forward. Some props have a "bump stop" of rubber or the like to make it quieter - mine doesnt. And mine has been clonking happily for 16 years.
 
Thanks for all your replies. I've just come back from a little over a week away in which I've covered about 250 miles. With wind anywhere from zero to force 5 or 6 (sometimes on the same day!) I've had experience of both motoring and sailing in a variety of conditions.

My experience of the new prop is as follows:

1) Yes it clonks going into ahead, but I know that that's ok now so it doesn't bother me.
2) The motoring performance ahead is as good if not better than the 2 blade fixed prop it replaced. That was an 18" x 15" and the Varifold is a 17" by 14", but I believe the Varifold has a larger blade area. It actually gives more boat speed than the old prop at the same revs, but the boat was just been cleaned off and antifouled so that will be a contributing factor.
3) Motoring in astern is good enough. On two occasions the prop has failed to open when (attempting to!) leave a pontoon, but a quick flick into ahead, then neutral, pause, and astern has had it working fine. It's never failed to open when moving from ahead to astern to stop the boat. Hopefully it won't.... Prop kick in astern is less than with the old prop.
4) Vibration levels are comparable.
5) Sailing - well, my wind speed indicator has packed up so I can't be truly objective but let's just say I'm passing boats that I really didn't ought to be passing! I'm also one of the last ones out there to give up on sailing and put the engine on.
6) No noise from a rotating prop when sailing as I can now lock the shaft by engaging reverse.

Conclusion? I love it! Highly recommended.
 
I found that greasing the gears on the Varifold seemed to make it stick in astern and it wouldn't open. Quick flick into forward would make it open. After a month or so the grease wore off and then it was fine always deployed.

May have been that I used the blue volvo stuff but next year I didn't bother.
 
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