Advice on Dyneema

Dave100456

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I need 20 metres of minimal stretch 'string' to run between the servo pendulum arm and steering wheel. This will be run through two blocks and because of the nature of SPS systems this movement will be frequent and prolonged.
I have decided to go for 5mm dyneema but the question I'd like answering is; how well will the unbraided dyneema stand up to the job or should I go for dyneema with a cover?
Thanks
 
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Daydream believer

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If you are talking of the control lines from something like an Aeries or Monitor I do not see why you want dynema. I use 8mm braid on braid OK & use my gear a lot. The only wear i get is right at the steering oar where the line sometimes nips between oar & line guide. If you do use dynema consider getting UV resistant, if not covered
 

GHA

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I need 20 metres of minimal stretch 'string' to run between the servo pendulum arm and steering wheel. This will be run through two blocks and because of the nature of SPS systems this movement will be frequent and prolonged.
I have decided to go for 5mm dyneema but the question I'd like answering is; how well will the unbraided dyneema stand up to the job or should I go for dyneema with a cover?
Thanks

Based on experience with more industrial applications I would say uncovered would be fine. UV isn't really a problem, that stuff's so strong even with a 50% reduction in strength it will still break something else before parting. 12 strand is easy to splice, but the splices need to be quite long, about 250mm for 5mm, so that might end up running through a block. I recently replaced my aries control line with D12 and wrapped the splice around the oar so that the splice didn't go through the lower block.
 

Daydream believer

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. I recently replaced my aries control line with D12 and wrapped the splice around the oar so that the splice didn't go through the lower block.

Thread drift here!!
If you did not go through the block on the lower strut ( I assume that is what you are saying)how did you direct the line to the deck. Did you totally bye pass the strut & go to somewhere on the transom & if you did , did it transfer the load from the oar properly
 

GHA

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Thread drift here!!
If you did not go through the block on the lower strut ( I assume that is what you are saying)

Not what I meant, it's rigged as normal but with an extra wrap around the oar so the splice doesn't go through the lower block.

While we're drifting.....

I also replaced the original blocks in the aries struts with these sheaves with bearings..
AL-1086 Ball bearing / sheave Acetal Resin
http://www.proboat.co.uk/item.asp?cat_id=45&prod_id=597&dep=1

Had to drill out for the 8mm aries pin but very little friction now, the old ones had masses of play in them after so many miles.

Yet to try it out in anger but feels very tight with less friction. A downside of dynemma is that with next to no stretch you need to leave a little slack as the length of the control lines isn't always the same when the till moves in an arc.
 

Dave100456

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If you are talking of the control lines from something like an Aeries or Monitor I do not see why you want dynema. I use 8mm braid on braid OK & use my gear a lot. The only wear i get is right at the steering oar where the line sometimes nips between oar & line guide. If you do use dynema consider getting UV resistant, if not covered

I've not installed or used a SP system before and maybe I'm foreseeing problems that won't exist. My worry was the long run with my setup I wanted to minimise loss of movement due to stretch which could negate the action of the steering arm. Over 20 metres even 2% stretch would be 400mm! Is this not worth consideration or is it good to have an amount of "give" in the system?
 

PuffTheMagicDragon

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Over 20 metres even 2% stretch would be 400mm! Is this not worth consideration or is it good to have an amount of "give" in the system?

I would imagine that, logically, only one half of the line would be under tension, so that already brings the maximum length down to 10 metres and maximum stretch would be closer to 200mm. However, bear in mind that to achieve that kind of stretch would require a load that is much higher than one can reasonably expect on a steering mechanism.
Consider this situation: My main halyard is around 25 metres (up and down the mast) and it is 8mm Liros Regatta 2000, a Dyneema SK78 core covered in polyester braid. If I put all my weight (75 kilos) onto the free end the stretch is not even 10mm; I have never had a load of 75 kilos on my tiller...
 

bjl

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If you prefer uncovered Dyneema but were worried about possible chafe you might consider covering just the lengths at risk.

As for sun degradation, I have used Amsteel Blue (Dyneema) in my kicker which has been exposed to the African, Caribbean, Bahamian sun for 30 months and does not yet need replacing. You might have similar success.
 
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Daydream believer

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Not what I meant, it's rigged as normal but with an extra wrap around the oar so the splice doesn't go through the lower block.

While we're drifting.....

I also replaced the original blocks in the aries struts with these sheaves with bearings..
AL-1086 Ball bearing / sheave Acetal Resin
http://www.proboat.co.uk/item.asp?cat_id=45&prod_id=597&dep=1

Had to drill out for the 8mm aries pin but very little friction now, the old ones had masses of play in them after so many miles.

Yet to try it out in anger but feels very tight with less friction. A downside of dynemma is that with next to no stretch you need to leave a little slack as the length of the control lines isn't always the same when the till moves in an arc.

Thanks for the bearing link. Anything to reduce friction is good so I will look at mine in the winter

Re the block- mine has 2 holes drilled & i pass the line through the opposite hole & tie a stop knot. I adjust tension at the last 2 blocks before the tiller as they are mounted on cords & can move to equalise the angles
 

maxi

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I have used 5mm Spectra/Dyneema for the past 15 or so years, connecting the wheel to the steering quadrant, running though 4 blocks either side, with no problems whatsoever except, there is initial stretch which demands some re-adjustment but this stabilises after a short period. 32' Maxi.
 

macd

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The OP doesn't say as much, but 20metres is a very long run for a servo-pendulum. Is the boat by any chance centre-cockpit? Whether it is or not, with that sort of length I'd defnitely go for the minimum stretch possible. Even the 200mm of potential stretch mentioned is a substantial proportion of the complete steering movement. With Dyneema, I'd also take special care to introduce a 'weak spot'.
 
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Ian_Edwards

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My experience (not in the marine environment) with dyneema rope in high wear areas, where the ratio of diameter of the rope to the diameter of the sheave is small, is that the cover wears off the core quite quickly, but once the cover is stripped away the dyneema core goes on for ever. The problems seems to be that the cover slides with respect to the core and bunches up as the rope oscillates over the sheave. Once that happens the cover fails quite quickly and can jam the sheave in the block.
So I now use uncovered dyneema rope.
If you look at the UV tolerance of the various synthetic fibres, dyneema comes out very well, and in practice I've never had a UV problem with dyneema.
 
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