Dyneema alternative to steering wheel chain?

[UNCIVILIZED]

Originally Posted by Training Wheels

I was able to use a Wichard shackle for my end fittings, fit perfectly. I used a flush Allen head shackle.

I'm thinking that ideally you'd bush the the shackle pin where it passes over the chain, using a bushing having a radius similar to that of the pin in the chain, so as not to point load things. Did you happen to do this? And what are your thoughts on same, given that you have hands on time with the system, & real world experience with this solution.

I say as much, since with shackles, their SWL is rated based on a certain percentage of the shackle's apeture being filled, so that there's not a big gap for the pin to span without something filling & supporting it (in theory). Thus the bending loads on the shackle pin are then lower. I'm curious to hear others thoughts on this.

[Stumble]

Originally Posted by malbert73

Yikes that chain is a disgrace. Why is it getting wet?

Also, not sure I'd worry about weight with steering system which is main reason to change to dyneema. Steel cable should resist abrasion better over years and years, no?

It isn't just weight. Dyneema doesn't require nearly as large a bend radius as cable which can make installations easier. Doesn't corrode which is always a nice addition, and it is trivial to keep a roll lying around in the event of underway repairs.

For stealing I would absolutely recommend a heat set variety due to its lower stretch characteristics.


So the downside is it is less chaff resistant... But if you have chaff in your steering cable then you need to fix it. This is a static installation, and chaff should have been worked out at installation.

[jack630]

Originally Posted by Stumble

It isn't just weight. Dyneema doesn't require nearly as large a bend radius as cable which can make installations easier. Doesn't corrode which is always a nice addition, and it is trivial to keep a roll lying around in the event of underway repairs.

For stealing I would absolutely recommend a heat set variety due to its lower stretch characteristics.


So the downside is it is less chaff resistant... But if you have chaff in your steering cable then you need to fix it. This is a static installation, and chaff should have been worked out at installation.

I don't think Dyneema is the right choice for this. Dyneema will slowly stretch under tension. You will be readjusting the tension all the time and chafe will be an issue even just going over a pulley. SS cable is the right material here.

[estarzinger]

btw, for the op, there are steering systems which are all dyneema (no chain). They use a drum to replace the chain sprocket. A machine shop could make up the required pieces for a retrofit, but it would be a bit fiddly custom sort of work, not a standard drop in piece. This is usually only done when people are looking to save every possible gram of weight.

I have seen dyneema, Vectran, and PBO all used in steering (instead of the ss cables). They each have pluses and minuses, they can all work satisfactorily, dyneema is probably the most common today. Like rigging, just size it big enough to control the various types of elongation. I personally think I would go with Vectran.

[Jim Cate]

If you decide to go with any textile cable, and your aluminium sheaves are corroded, replacement is in order, for the corroded pits will not be nice to the cable. And if you are replacing the sheaves, be sure to match the groove size with the diameter cable that you select.

Jim

[arsenelupiga]

Originally Posted by UNCIVILIZED

I'm thinking that ideally you'd bush the the shackle pin where it passes over the chain, using a bushing having a radius similar to that of the pin in the chain, so as not to point load things. Did you happen to do this? And what are your thoughts on same, given that you have hands on time with the system, & real world experience with this solution.

I say as much, since with shackles, their SWL is rated based on a certain percentage of the shackle's apeture being filled, so that there's not a big gap for the pin to span without something filling & supporting it (in theory). Thus the bending loads on the shackle pin are then lower. I'm curious to hear others thoughts on this.

I have gone thru above thinking when replacing with dyneema. Used 2mm dyneema to link shackle for dyneema and chain with enough turns assuming loss of 50 % strength. If remember correctly, done 6 circles which perfectly spread thru the width of chain pin after put under tension and total strength of link remain equal to 6mm dyneema ~ around 4T. So no weak point there.

[bad.wabbit]

I went through a steering system rebuild and replaced the chain with new chain and the wire with heat set dynema. I don't think Edson chain is stainless - read the description closely. Besides that, the 304 or 316 chains are much weaker than the steel chains.

I have a rebuilt 6" adjustable idler available that may work for you. Bronze pulleys that will not corrode like your aluminum ones. PM me if you are interested.

[Lambada]

Tiller best solution for ships up to 13 metres

[Stumble]

Originally Posted by jack630

I don't think Dyneema is the right choice for this. Dyneema will slowly stretch under tension. You will be readjusting the tension all the time and chafe will be an issue even just going over a pulley. SS cable is the right material here.

Heat set dyneema does creep under load, but you are taking a technical fact and expanding it to a practical issue without understanding what is going on. Creep is the permanent lengthening of a material under constant load, and for dyneema is exponential with load (relative to MBL). But to make the math easier lets assume a linear not exponential rate.

A typical 50' HRS dyneema shroud will carry 10% of its MBL and have .1" of creep elongation per year. Thats .1"/600" or a creep rate of .0001666% of the total length per year.

A dyneema stearing cable of 7mm will have a MBL of about 18,000lbs but only be pretensioned to about 150lbs. or ~1% of the MBL. It should be an exponential decrease in creep but lets run it linerarly just to make it easy. Stepping down from 10% to 1% MBL would then mean a reduction in creep from .0001666% to .00001666%.

Assuming your steering cable is 15' long that would mean a yearly increase of .0002 inches a year. That is 2 TEN THOUSANDTHS of an inch. No one in the world is going to be able to feel the amount of length increase. It would take some pretty accurate scientific gauges to even measure that length.

So why use such a strong rope? Technically you could use a smaller line and be fine, but generally if you swap steering cables you might as well swap size for size. Any weight savings will be meaningless, and the HSR in this size, while expensive, doesn't effect the price of the project much.