guard wires or rope?

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FergusM

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Has anyone used terylene rope (or other fibre) instead of wire between the stanchions?. The wires on my boat are due for renewal, and I was wondering about using 6 mm line instead. I remember back about 1970 reading in the PBO about a sheathed terylene sold by ICI under a name like Parafill, which they reckoned would be ideal for standing rigging. A couple of years later they were marketing it for use as guard lines. This would suggest that terylene is plenty strong enough. I suppose chafe might be a concern, but that can be dealt with. Are there any other drawbacks to rope?
 
Well - the Chafe from the foresail might be an issue, it currently rubs through the plastic coating around our wire.
The shock load would need to be evaluated - a wirerope may have similar max loading, but what happens when you topple over the side whilst clipped on or fall into the rail?
UV protection would be another concern - wire doesn't suffer as much as standard rope sheaves, so you might be replacing more often than a wire equivalent?
 
It is best to use Spectra. Splice an eye in one end but not the other as that end has to be fed through the stanchions. On that end tie a bowline and lash to pulpit/pushpit (bowlines do not reduce the strength by 85%, as has been claimed by another).

Steve Dashew (and others) describe what they have done Here.

I have also seen polyester used (ie dacron/terylene) on older boats with no apparant problems.

All these lines last a long time even in high UV areas.

If you intend to race, however, note that lifelines must be stainless steel in order to meet any Category of the International Sailing Federation Offshore Special Regulations.

John
 
I've used 5mm Spectra on my guard rails for the last 5 years.

The advantages are a far lower weight, greater breaking load than the equivalent diameter of plastic-covered stainless, lack of injury when you get thrown against them in a seaway and people tend to respect your gurdrails more when coming alongside.
Price per meter is about the same as plastic covered wire and you therefore save on the end fittings.

Disadvantages are that you get chafe wear at the stanchion eyes, sooner than with ss wire, you need to tighten the guard rails more frequently, you cannot effectively attach your fenders to them and life expectancy is lower, due to uv degradation, than with ss wire.

Anything but Spectra or Dyneema will be unsatisfactory due to stretch
 
Sorry Ships-Cat, but "(bowlines do not reduce the strength by 85%, as has been claimed by another)." is quite incorrect - go to the New England Ropes site and search for their test data, or try Brion Toss - the average failure of the best tested knot was 85% reduction in strength.
As far as splicing goes, the brummel splice can easily be formed in place without any special tools - it's detailed on neropes also.
 
Not sure where you get your figues from either!

The New England Rope Site gives RETAINED strength NOT LOSS as a percentage and they say a Bowline gives 67-75% of the strength of the original line.

Here below the table from the New England Rope site - sorry I haven't preserved the formatting, but I hope that its obvious what goes where.

Knot Strength Type of knot, bend or hitch Percentage of retained strength
Bowline 67-75
Anchor Bend
Over 5/8" dia. ring 55-65
Over 4" dia. post 80-90
Two half hitches
Over 5/8" dia. ring 60-70*
Over 4" dia. post 65-75*
Square Knot 43-57*
Sheet Bend 48-58*
Fisherman's Knot 50-58
Carrick Bend 55-60

*Smaller sizes of nylon are liable to slip
without breaking
*Both nylon and P/D combination ropes in
smaller sizes are liable to slip.

Hence what I think you should be saying is, 'According to New England Ropes research, a bowline reduces the breaking strain of a line by 25-33%'.
 
[ QUOTE ]
Sorry Ships-Cat, but "(bowlines do not reduce the strength by 85%, as has been claimed by another)." is quite incorrect - go to the New England Ropes site and search for their test data, or try Brion Toss - the average failure of the best tested knot was 85% reduction in strength.
As far as splicing goes, the brummel splice can easily be formed in place without any special tools - it's detailed on neropes also.

[/ QUOTE ]

As this is so far from theoretical figures and practical experiences I'd suggest either the site is incorrect or you're transposing figures ie bowlines retain 85% of their strength, the loss therefore being 15%.
 
I agree with the answers others have given regarding the knot strength.

Regarding splicing both ends of the rope lifeline, as you say there is no problem splicing it after feeding it through the stanchions. However, it is possible to make lifetime adjustments for length due to stretch and the creep from just one splice if a bowline is used (assuming one stays with the recommended maximum lashing length of 100mm when first setup).

John
 
Parafil is an older line used and is as you say plastic civered synthetic ... when broken open - it may resemble more fibres than a laid rope ...
 
[ QUOTE ]
A respected and knowledgable owner of my aquaintance uses stainless for the upper line and rope for the lower. His is a very well found ship.

[/ QUOTE ]

That's how my boat is set up ! /forums/images/graemlins/grin.gif
 
Sorry guys - agree entirely about bowline strength, however in low-tech fibre, and not in Spectra. If you search further, you'll find the experts talk about knots in spectra behaving much like knots in wire. In nylon, polyethelene and dacron fibres for example, the individual fibres stretch within the knot and allow the fibres to balance and share the load. In specra, vectran, kevlar and pbo, there is negligible stretch, and therefore the fibre (note singular) on the outside bears all the load until it snaps, then the next does the same etc.

If you still disbelieve (I teach people this info as part of splicing hi-tech ropes), then do yourselves a simple test - get a piece of spectra about 3 metres long - any small diameter will do, but 2mm or 3mm would be good. Do a brummel splice at one end and drop it over a solid point onboard, and lead the tail to a winch (doesn't need to be a big winch). Give a trial grind to satiisfy yourself that you can't break the line at a load similar to it's BS. Now tie a knot in the line, and retest.

I recently spliced an eye into the end of a 10mm spectra headsail halyard, where the rigger (that's what he calls himself but I doubt his quals now) had tied a bowline to a shackle. The owner, 66 years old, broke the halyard pulling the headsail up, using a Barlow 16 winch (about the size of a Lewmar 8 I think) with an 8 inch handle. The line had a breaking strength of 2300kg.

Another example I use is that if you were to replace a 6mm ployester halyard (800kg BS) with a bowline at the head, what diameter spectra would you need? Answer is 10mm, with a 4150kg BS. The 6mm polyester should have a retained BS of at least 550kg, whereas the spectra (at 85% loss) is only 630kgish, and the next size down (8mm) would only give 415.
 
Just talk to anyone who's flown gliders (tow launched) or has climbed. You'll soon receive perceived knowledge on knots and splicing. Anything that introduces a weak link is perceived as a problem. Knots are, splicing is, but less so.
 
So you are now saying that the references you previously gave to back up your claims as to strength loss for Spectra knots, actually do not apply to Spectra? But if WE ...search further, you'll find the experts talk about knots in spectra behaving much like knots in wire.?

Perhaps you would like to give some links to this next lot of experts you are now referring too? I could only find papers and documents that raised no special issues with respect to Spectra compared to other materials.

For example, the closest I came was http://www.acmgguides.com/pdf/Comparative%20Testing%20of%20High%20Strength%20Cord.pdf, a technical paper, shows Spectra performs poorly for figure of eight (knot efficiency 53% though), but as as well as others for bends and friction knots (a bowline being a friction knot, however it does not specifically test a bowline).

In that same paper they give the results of flex cycle tests and you will see that contrary to the findings for Kevlar (which is widely known to perform badly when cycled in flex and also in sharp bends such as in knots and around small blocks), Spectra performs almost as well as nylon and does not show the same precipitous drop off of strength that Kevlar and Kevlar/Spectra mixes do.

It may be that you are thinking of Kevlar?

There is also a wealth of material from rescue and fire departments on the use of ropes and knots (it seems high modulus materials are in wide use with them) and I have not found one that raises any special knot issue over the use of Spectra compared to other materials.

I was already aware of one reference to a bowline in Spectra failing (it is on the Pardey's site) but that was a case of slippage allowing it to work loose when a halyard and bowline was used to hoist a man. They also note that the lesson applies to other ropes as well.

I did learn something, and that is that Spectra is now widely used in recreational climbing. But again no special warnings regarding knots that I could find.

John
 
Bowline strength

[ QUOTE ]
Hence what I think you should be saying is, 'According to New England Ropes research, a bowline reduces the breaking strain of a line by 25-33%'.

[/ QUOTE ]

Careful. Some years ago I strength tested a range of bowlines to establish whether there was a significant difference in strength between 'inside' and 'outside' bowlines (defined by whether the tail is in the middle of the knot or on the outside). There was no significant difference.

However, when I tested the loss of strength of different types of rope, there were significant differences. The loss of strength in a knot is usually because when the rope is bent the fibres on the outside of the bend come under a greater tension than those on the inside of the bend. The difference in tension, though, depends on the elasticith of the fibres. Elastic ropes (such as nylon) suffer relatively little loss of strength, while the loss on non-elastic ropes (such as Kevlar, Spectra or Dyneema) can show a considerable reduction.

Any research that just quotes a single figure for loss of strength can be quite misleading. It should at least specify the ropes used in the tests, and should preferably quote results for each individual type of rope rather than just quoting a range of strength losses.
 
No not at all Brendan. Just making comparisons between ropes so as seen the loss from knotting Spectra is not disasterious as has been claimed.

As you said in your first post, knots and splices reduce strength without question. I am only referring to the loss in Spectra when compared to other materials such as polyester and nylon.

Carrying on from PeterB's post it is known that Kevlar suffers from flexing and sharp bending (as it does in composite structures as well), but it seems that Spectra/Dyneema is not nearly so susceptible.

In the reference I gave there are flex tests (there is also a link in that reference to the detailed measurements) and that shows a precipitous fall off in strength for the likes of Kevlar after flexing. They make the point that may make knots more efficient though. While Spectra (Dyneema) does show a loss of strength compared to nylon (which has no loss) when flexed, it is not alot (especially when one considers its initial strength advantage of around 3x over polyester and nylon) and the drop is not precipitous and it stabilises.

I think the flex results are important as it is one indicator of how well the material will work when bent into a knot with the flexing that then occurs as the knot is loaded and unloaded.

That same paper has some interesting results with respect to knotting tapes - seems not as fearsome as many think.

Just out of interest there is an excellent document on the Samson Rope site on rope strngths and selection for yachts that people may be interested in - http://www.samsonrope.com/home/newrecmarine/srt_selection_guide_2.pdf. Discovered that some time ago when specifying some lines for a client (they wanted Samson).

John
 
I am very wary of rope based safety lines. Three years ago went over the side whilst picking up moorings, from a yacht which had been land bound for several years. Was leaning on the upper guard rail whilst stretching with boathook, when the whole lot gave way. Rope had suffered UV degradation, nearly as much as my own reputation. I wont have any rope based safety rails and that includes nylon chordage to tension the line. Stainless and bottlescrews to boot!
 
Actual numbers from actual load tests done 10 days ago using a 7mm SK62 Dyneema 12 strand Braid not covered i.e. not a double briad.

These tests were done in responce to a sudden burst of rope failures on trailer winches.

Strop with Brummell each end 24.6kN
Strop with Round turn and 2 1/2 hitches onto a 12mm shackle each end 8.8kN
Strop with R/turn/2 halfs again onto 12mm shackle one end and fishermans knot onto 12mm shackle other end 6.7kN
Strop with bowline each end 10.7kN.

Numbers are average loads achieved of 3 strops in each configuration. Loads were applied in a gadual but quickish manner in a hydrualic test bed, not shock loaded. It is generally accepted shock loads are the worst sort of load to have. Each strop had 1 metre of clean line between the terminations.

The Brummell loads were around 18-20% below the yarn manufacturers calculated rope strength for an un-spliced rope. All the break points in all the strops showed obvious signs of 'glazing' meaning the rope strength would have been compromised to some, possibly a fair bit, degree even if the rope was not pulled to destruction.

Conclusion - knots and Dyneema don't mix. Brummel splices, done right, lower Ulitimate Break Load's as would be expected from any good splice on most ropes.

In round figures 1kN is 100 kilos (220lb)

Ships Cat - if you have a look around the trailer boats you will see what I mean. Blue, Green, Orange and Yellow ropes are all spliced and the red ones are knoted. The Red ropes are the ones with the issues and new to the market.

The colours are purely a dye in the coating and have no relationship to rope strength.
 
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