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415 Singapore View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 415 Singapore Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2021 at 12:58
Hi, following the Jefa instructions, I took everything apart today and took the chains out. They and the cog wheels were in remarkably good condition for 7.5 years use and I could see no mechanical reason for our wheel to have slipped round. Looking at the depth of the teeth on the cog wheel I really don't think it is possible for the chain to jump a cog as there are a minimum of 4 or 5 teeth engaging the chain at any one time.
What I think is more likely is that whilst the system had a little slack in it, this was increased by the amount of weather helm and tension in the active cable when a 30 knot squall hit usgoing upwind. When we tacked onto port tack the weather helm meant we didn't require much helm input and I think the cog wheel grabbed the next link in the slack chain before the tension came on. This kink in the chain would then pass over the cog wheel easily and without you feeling anything.
Below is a sketch of what I mean, note it isn't accurate and doesn't show the correct number of teeth.
Any thoughts would be gratefully received
All the best
Paul

Paul - Night Train - 415 #136
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DJgun View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DJgun Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2021 at 14:37
even if there is slack in the cable, there is still weight in the chain and cable which should not allow that to happen. ....unless the cable is so stiff and constrained laterally that it can actualy push up on the chain.  It does seem highly unlikely. 

However, if the cables were extremely loose, and the loads on the steering very high, it might be possible to jump a tooth. But that means radius change approx one roller diameter, which equates to VERY loose cable. The pressure angle of the sprocket tooth on the chain rollers does have a component trying to push the chain outwards. That is worse on sprockets with small tooth number. With loose cables, high loads and maybe some system deflections and elastic elongation it is remotely possible a tooth hcould be jumped.

I inspected a twin steer, twin rudder boat with Hefa steering not long ago, where a tie bar between the quadrants was adjusted, and that immediately lead to a big difference in the wheel alignment.
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415 Singapore View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 415 Singapore Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2021 at 14:51
Hi DJ, thanks for the reply, the cables / chains were not excessively slack. In fact when inspected in the marina with no load I would suggest that they were the correct tension, possibly slightly loose but certainly not unduly loose, vertical movement in the middle of the longer run between the two wheels was about 2-3 cms max. 
You say my theory is unlikely, but to be honest I believe it more likely than the chain jumping 4-5 teeth which as you say means that that radius changeis large.
I have sent all the photos etc to Jefa and will see what they say
All the best
Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DJgun Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2021 at 16:09
Hi Paul, 

it will be interesting to hear what Jefa think.  Good luck.

Cheers
DJ


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 415 Singapore Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2021 at 12:54
Hi, having sent photos and videos to Jefa, they seem to be at a loss as to what happened too!Reply I got:-

Hi Paul,

I donít think the ĒkinkĒ is a possibility, but I may be wrong. The chain looks good and greased, so nothing wrong with that.

I donít know what to do about your case now. It may be a once in a lifetime occurrence.

 Med venlig hilsen / Best regards


Nothing broke, and it wasn't a safety issue, so I guess I will just monitor it, the upside is I now know how to remove the chains and cables without having to take the boat apart!
All the best
Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote S&J Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2022 at 10:17
Hi Paul,
Just a follow up to see if you were able to reinstall the cables so that your original "straight ahead" position of the wheel was returned.

I was hit by a 56kt squall last year and afterwards my starboard wheel appears to have rotated exactly as yours did.  My steering cable tension all seems as expected and other than the wheel misalignment nothing appears wrong.

I'd like to be able to return the wheel to the original position so there is no spoke obstructing the MFD display at the straight ahead position.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 415 Singapore Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2022 at 11:27
Hi Stuart, I think it is possible to return the wheel to the original position, you would just need to take out the cog wheel from one wheel and move the chain over one link. I didn't bother as when I inspected both wheels the chain / wire connections were in similar positions with the wheels hard to port and starboard. So I think that the system was originally tensioned one tooth out.
Might be worth reporting it to Jefa as they suggested my problems were once in a lifetime!
Glad that was the only issue in 56 knots!
All the best
Paul
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415 Singapore View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 415 Singapore Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2022 at 11:55
Hi Stuart, your post made me think about this again. I wonder if the problems comes about by the system being incorrectly installed in the first place? If being one tooth out in the original set up exasperated the issue when we were both under extreme weather helm situations?
All the best
Paul
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DJgun Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2022 at 15:55
It seems Jefa/Hanse should have a look at this problem, when it has happened on 2 separate boats.

I must confess I am still surprised they use 11Tooth sprockets in this application.  With wheels connected, if the two sprockets are tooth aligned relative to each other when play is adjusted out of the system then there will be significant "cogging" in the chain tension, due to simultaneous polygonal action in the chain on both sprockets. 

I suspect the least problematic setup with 11T each side would be to have the sprockets 1/2 tooth displaced from  each other.. 

Generally Jefa seem to implement well engineered products, and I really like a lot of their design. But is seems there are issues with this implementation.


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