Dyneema Gates ( lifeline , life line , guard rail )

[geem]

Unless your boat is stored in a lightless, vacuum chamber things wear no matter how many miles you travel.

To check this please visit any 'boat graveyard' and see the wear and tare on hulls that have not moved in decades.

I climb in and out of the dinghy using the guardwires every day. The dinghy is hoisted each night and sits against fenders that lean on the guardires. At anchor, the main halyard is tied off to top guardwire. All these things cause movement of the guardwires but in 12 years there is not a single broken strand. If the boat sat there, unused, none of this movement and load would exist. Using the boat everyday creates wear. I don't believe dyneema would suit the way we use the guardwires. It would fluff up rapidly at the stanchion holes. Our mizzen dyneema runners wear where they contact anything, but being 8mm thick, they can take some wear. This size rope wouldn't be possible on the guardwires due to the hole size in the stanchion.
Additionally, the props for our guardrail mounted solar, sit on the bottom guardwire. These props are timber. The props get adjusted through the course of the day. There is zero wear on the guardwires. Dyneema would be the wrong choice for us.
Dyneema has its place. All our halyards are dyneema. We have dozens of dyneema soft shackles and our guardwires are lashed with dyneema. I am a big dyneema fan but only where it makes sense

 

[dunedin]

........We don't have a gate because we want guardwires super tight. These are our primary safety devices for keeping people on the boat.......

But I think you spend most if your time ocean sailing and in Caribbean anchorages.

Coastal cruising boats have people going on and off onto pontoons or docksides a lot. I suspect more people are hurt slipping/ falling when going over high guardrails than are hurt or worse as MOB. Know of quite a few hospitalised falling when going ashore, and rescued a couple of in marina MOBs where people tripped over guard rails.
Gates help a lot with high freeboard boats.

 

[KimB]

I have.

They are brilliant. Soft in the hand, stronger than steel and the ones I made up have a reflective thread in the outer layer allowing you to see where the guardrails are on a dark and stormy night, and on the way back from the pub, from the light of a torch.

I'd never go back to metal lines.

Thanks - I like the idea of the reflective thread in the outer layer - genius! Do you have gates? and if so which clip device did you use? Thanks again - Kim.

 

[KimB]

I climb in and out of the dinghy using the guardwires every day. The dinghy is hoisted each night and sits against fenders that lean on the guardires. At anchor, the main halyard is tied off to top guardwire. All these things cause movement of the guardwires but in 12 years there is not a single broken strand. If the boat sat there, unused, none of this movement and load would exist. Using the boat everyday creates wear. I don't believe dyneema would suit the way we use the guardwires. It would fluff up rapidly at the stanchion holes. Our mizzen dyneema runners wear where they contact anything, but being 8mm thick, they can take some wear. This size rope wouldn't be possible on the guardwires due to the hole size in the stanchion.
Additionally, the props for our guardrail mounted solar, sit on the bottom guardwire. These props are timber. The props get adjusted through the course of the day. There is zero wear on the guardwires. Dyneema would be the wrong choice for us.
Dyneema has its place. All our halyards are dyneema. We have dozens of dyneema soft shackles and our guardwires are lashed with dyneema. I am a big dyneema fan but only where it makes sense

Good points - we are having new additional solar so your point would affect us too. Thanks, Kim.

 

[KimB]

Utter rubbish !

I've had 6mm dyneema guardrails for 3 years now, no wear, as strong if not stronger, kinder to peoples legs and hands and cheaper too if that matters
I have stainless thimbles lashed to pelican hooks at the pushpit end

Thanks I've read about some "different" Pelican hooks so it's good to hear of your experiences. Kim.

 

[lustyd]

stronger than steel

While I'm not arguing against dyneema here, this comment always bugs me.

For a given diameter brand new dyneema is slightly stronger than stainless wire, that is absolutely true. To maintain a minimum breaking strain equivalent to steel over a long period though, you'd need to overspec the diameter due to the various other properties of Dyneema. It's great stuff but any scuffing or cutting will reduce the strength considerably and while stainless will have surface rust it won't degrade as much.

Not that it matters, if the guard wires are used for anything more than hanging fenders then something has already gone seriously wrong, and it doesn't take 2 tons of breaking strain to hang 4 fenders!

 

[Neeves]

Apologies KimB

I omitted to mention, we had a cat with transoms large enough to come along side with a dinghy. We had no need for a gate in our lifelines.

When we had a monohull we raced it and were agile enough to climb over lifelines (and dyneema was not approved for lifelines - though this may have changed)

If you fly a spinnaker it is possible that the sheet will rub on the life lines and the lifelines can be cut - simply with the friction 'melting' the dyneema.

If you are changing from stainless to dyneema you do need to ensure that the holes through the stanchions are really smooth and have not been scored by the stainless (as this will obviously be a focus for abrasion of the dyneema)

Jonathan

 

[Sandy]

Thanks - I like the idea of the reflective thread in the outer layer - genius! Do you have gates? and if so which clip device did you use? Thanks again - Kim.

No gates here, I get into the boat via the stern swim ladder on the transom.

 

[Sandy]

While I'm not arguing against dyneema here, this comment always bugs me.

For a given diameter brand new dyneema is slightly stronger than stainless wire, that is absolutely true. To maintain a minimum breaking strain equivalent to steel over a long period though, you'd need to overspec the diameter due to the various other properties of Dyneema. It's great stuff but any scuffing or cutting will reduce the strength considerably and while stainless will have surface rust it won't degrade as much.

Not that it matters, if the guard wires are used for anything more than hanging fenders then something has already gone seriously wrong, and it doesn't take 2 tons of breaking strain to hang 4 fenders!

Errrr mmmmm...

The loads of my 90 kg body with all my gear on being forced against the lines by 'a big green' on will be nowhere near 2 tonne, but I will have seriously cocked up.

 

[Refueler]

Errrr mmmmm...

The loads of my 90 kg body with all my gear on being forced against the lines by 'a big green' on will be nowhere near 2 tonne, but I will have seriously cocked up.

The load on guardwires / lines is not the real issue - when it comes to falls ... its actually whether the stanchions stay in place ...

Many boats where there is no alloy hull - deck toe-rail joiner - have basically machine screws into GRP. My 25 had one rail pull out when a person fell back and grabbed the guardwire - Parafil .. the wire held but not the stanchion. There was nothing wrong with any of them - it was design fitting - similar to many other boats ..
Not only the stanchions mounting - but also the height !! Not exactly high enough to keep you in ..

I certainly do not regard guardwires as a total stop to prevent falling overboard .. I regard them as a GUIDE wire to assist staying on board.

 

[lustyd]

Errrr mmmmm...

The loads of my 90 kg body with all my gear on being forced against the lines by 'a big green' on will be nowhere near 2 tonne, but I will have seriously cocked up.

Not really true. You'd be putting 250KG of tension on the line if you were hanging statically from it, assuming a 10m wire, and that's assuming a 1m sag in the line. Add in any force of a fall and you'd easily hit 2 tons.
You're not hanging from a rope, you're pushing the middle of a line so the physics calculation is different.

 

[Refueler]

Not really true. You'd be putting 250KG of tension on the line if you were hanging statically from it, assuming a 10m wire, and that's assuming a 1m sag in the line. Add in any force of a fall and you'd easily hit 2 tons.
You're not hanging from a rope, you're pushing the middle of a line so the physics calculation is different.

I'm trying to figure out where 160kg comes from ...
A static hung body of 90kg creates a load of 250kg on a 10m long wire.......

I regularly hang models from static horizontal line to gauge thrust etc when testing motors / props ... when I hang that 5kg model - the line of course sags - its impossible to have a perfect straight line when a weight is suspended from its mid point .. old school physics lesson !
My model weighs 5kg ... the fishing scale used to measure the total line / model before test when model is hanging shows 5kg ...
Given your statement - it should read 14kg ..... ????

But I agree that when you fall against the wire - that's a completely different ball game as the shock load can easily be a high multiple of the body weight - especially if a wall of greeny is also shoving you !

 

[Sandy]

You really need to compare like with like.

Now what about the breaking strain of that connecter - that will be the weakest link.

 

[lustyd]

its impossible to have a perfect straight line when a weight is suspended from its mid point .. old school physics lesson !

It's impossible because the tension on the line tends towards infinity the closer you get to having it straight. That's the lesson you're talking about and there's a formula to calculate. I used an online calculator for line tension. If both sides of the line are vertical then the tension in each is half the weight of the object, but as the angle gets closer to horizontal the tension increases exponentially (but not the system weight, obvs).

As Scottie once said, Ye cannae change the laws of physics captain!

It's obviously much more complicated in the case of guard wires, the length of the section is not 10m but then it's not attached at the stanchions so the calculation becomes more difficult, but the principle remains the same. Assuming you could keep the wires bar tight and they were very strong, they'd then transfer the (approaching infinity) tension to the pullpit and pushpit, which would likely lever themselves out of the deck. Thankfully, bar tight isn't an option and there is stretch, and there's only (hopefully) a temporary force against the wire, giving time to stop falling overboard.

If you fall sideways against them it's better since there is an angle from pushpit to the widest part of the boat, massively reducing forces in the wire. Vertically though the wires are straight.

 

[Refueler]

OK .. yes the line itself experiences stress approaching infinity as it approaches straight.

 

[thinwater]

Not really true. You'd be putting 250KG of tension on the line if you were hanging statically from it, assuming a 10m wire, and that's assuming a 1m sag in the line. Add in any force of a fall and you'd easily hit 2 tons.
You're not hanging from a rope, you're pushing the middle of a line so the physics calculation is different.

^^ ^This. Under the force of a hard, sliding fall, the wires take the impact and the stanchions hold the wire spacing. As for wire tension, there is a tight rope effect, and the tension will be 4-6x greater than the impact on the guard rail, which will also be several times body weight. one ton is realistic and the rest is safety factor and allowance for wear/fatigue/corrosion.

I have had both Amsteel and stainless on my last two boats, at the same time. A few thoughts:

• We don't hang fenders on lifelines or use them for climbing. That's a good way to get leaks.
• The Dyneema sections are places where lifelines would be useful but were not included by the manufacturer. For example, on my F-24 I added Dyneema guard rails where the outboard tips up and extensions from the pulpit and sternrail (trimarans often don't have guardrails on the amas).
• You can attach Dyneema to stanchions with luggage tags and other tricks that would require welding with stainless lifelines.
• The life expediencies vary with both, but 20 years seems realistic with stainless and 10 years with Dyneema. Stainless corrodes in the sockets and is prone to kinking. Dyneema wears and is affected by UV, but going 1-2 sizes over buys a lot of allowance. We went oversize with Dyneema, because it is more comfortable to handle and still very light. None are less than 6 mm. On both boats, the main sections are stainless.
• Tension. World Sailing gives a figure for tension. More than that only increases the tension during a fall and bends the stanchions inwards. Slack is bad, but overly tight is also poor practice. If a gate reduces tension then the gate is very poorly adjusted; I don't understand the comment.
• Gates vs. no gates. Yes, a gate is a potential failure point. One the other hand, gates can also enhance safety. Recovering an MOBs through a gate is loads easier and there have been many, many nasty falls caused by tripping over a lifeline while boarding. I think the net advantage clearly goes to gates for most cruisers. Racers are free to feel differently. If any of the crew are very short, elderly, or disabled, no gates often mean no safe sailing.

I like stainless. It lasts. But there are places for Dyneema.

 

[thinwater]

OK .. yes the line itself experiences stress approaching infinity as it approaches straight.

But ...

• The line is not straight even in theory. The hulls of boats are curved.
• SS and Dyneema stretch.
• Sternrails and pulpits flex. They bend under peak load (very few pulpits are designed to take a 5000-pound load in the direction of the wire without failure--also tested by Practical Sailor).

I did measurements on several boats, and the answer is 4-6x. It is very unlikely the wire will see a force over 1500 pounds and it is likely stanchions and the pulpit or sternrail will bend. In the end, the strength requirement is a consensus figure that has resulted in durable lifelines.

In fact, jackstays/jacklines are subject to much higher loads, because they are straight and because the end points don't bend. They are less subject to hidden chafe.

 

[lustyd]

The line is not straight even in theory. The hulls of boats are curved.

Monohulls are, yes. Multihulls are pretty straight these days. Only in one plane though so if you land vertically they are in fact straight.

In fact, jackstays/jacklines are subject to much higher loads, because they are straight and because the end points don't bend

Most well designed jackstays aren't even close to straight, they go along the side decks and when you pull on them you'd be on top of the boat anyway so usually most of the force isn't even on the jackstay. Add to this that jackstays aren't tight and are more elastic and the forces will be much lower than a guard wire.


All are obviously strong enough for the job though. I only raised the tension thing because someone hadn't understood the scale of the forces involved which could lead to poor decisions being made. As you rightly said, upsizing the dyneema gives a lot of leeway anyway.

 

[thinwater]

Monohulls are, yes. Multihulls are pretty straight these days. Only in one plane though so if you land vertically they are in fact straight.

Even a very small deviation from straight makes a big difference in the math. Trig, or even Pythagoras.

Most well designed jackstays aren't even close to straight, they go along the side decks and when you pull on them you'd be on top of the boat anyway so usually most of the force isn't even on the jackstay. Add to this that jackstays aren't tight and are more elastic and the forces will be much lower than a guard wire.

I can't agree with that. a jackstay that is so loose that you can move it about is not well designed and won't provide much security. There are probably boats like that. Normally there is a lashing that pulls them snug.

Our most epidemic poor practice, IMO, is attaching jackstays to the bow and stern cleats. You don't attach seat belts according to where it is convenient, you put them where they are needed. Jackstays should always have dedicated anchors so that they can be in optimum positions. Bow and stern cleats (a) are not generally in the best place and (b) have other purposes for which they should be available.

All are obviously strong enough for the job though. I only raised the tension thing because someone hadn't understood the scale of the forces involved which could lead to poor decisions being made. As you rightly said, upsizing the dyneema gives a lot of leeway anyway.

See above

 

[lustyd]

I didn’t say loose, I said not tight. If my jack stays were as tight as my guard wires I wouldn’t be able to clip on to them. They’re also made of polyester so have considerably more stretch.
You don’t have to attach to cleats to run up the side decks, I have dedicated anchors at bow and stern.