Dyneema backstay with integral SSB antenna

[poiu]

I'm planning the big re-rig this off season. I am probably going with discontinuous rod throughout, replacing what is already there. It occurs to me that I could fit a dyneema backstay instead of the rod for the following reasons:

• The backstay is already highly adjustable by a large turnbuckle and a hydraulic ram, so any problems with stretch or creep can easily be dealt with.
• A re-do of a brummel splice would be possible on the back stay with the rig up, so again any stretch concerns can be dealt with.
• There is nothing to abrade the back stay or crash into it, so it is free from the damage the shrouds in particular potentially suffer.
• It is light and will save me about 28kg, mostly high up.
• It can (possibly) have an integrated internal SSB antenna in the form of a single PVC insulated wire of similar gauge to the copper in the GTO-15 and so save the extremely expensive cost of insulators in the rod of size -48.

Any thoughts on this?

I wonder if the heat from a transmitting SSB antenna would be harmful to the dyneema - how hot will a wire get?

Also, would the wire in the backstay cause a harmful stress riser as it exits the rope at the bottom end?

[estarzinger]

Originally Posted by poiu

.[*]A re-do of a brummel splice would be possible on the back stay with the rig up, so again any stretch concerns can be dealt with.

Best practice is not brummel; just a straight bury with excellent long taper bury and a little sewing. But if you like the brummel that's fine too it causes a little strength loss but since you have the wire exit stress riser (discussed below) it is not important in this application.

I wonder if the heat from a transmitting SSB antenna would be harmful to the dyneema - how hot will a wire get?

Will be fine - dyneema is totally good up to 80C - and even at that temp the strength loss only occurs after continuous hours of it.

Also, would the wire in the backstay cause a harmful stress riser as it exits the rope at the bottom end?

There will be a little strength loss there. The very maximum it could be is 20% loss (80% strength left). Just factor that in. But you are usually way over strength already in order to minimize stretch/creep.

Net - its a fine thing to do.

.............

[poiu]

Originally Posted by estarzinger

.............

Thanks for your comments. You are prompting me on another important issue. I'm not sure there will necessarily be a lot of residual strength. As the force on the backstay is controlled by the hydaulic cylinder pressure it is possible to dial it down when not sailing, so reduce the loads and ensure there is no little term creep. To help further I was considering getting the Gleistein DynaOne HS Max. This rope is one of the new DM20 ropes that are emerging on the market. It has negligible creep and if sized to match the strength of the rod then there will be little strength headroom. Their 16mm rope having a breaking load of 23.5 daN and the Navtec -48 is 21.8 tons.

Stretch is a key factor. The dyneema with my 25.5m long backstay will have a stretch of 76mm at 10% load, whereas the rod has 17.5mm. An important question is how much stretch is OK in a backstay with a very stiff mast. To match the stiffness of rod I would have to go to massive sizes of dyneema, about 32mm diameter compared to the 14.3mm of the rod. About 4 times the breaking strength. Any thoughts?

[UNCIVILIZED]

You should call, repeat, call, Colligo Marine & discuss this with them. I had an OUTSTANDING chat with the head of the company recently. Concerning, ironically, switching from rod to Dux. And he was more than pleasant to talk to, & went way above & beyond to field all of my questions. Some of them quite technical, due to my extensive involvement over many decades, with what makes boats & rigs "tick".

Dux gets sized to match up (or well exceed) the stretch of the metal rigging that it's replacing. So in terms of overall diameter, yes, your backstay will be quite a lot thicker. But given my chat with Colligo, going to synthetic rigging is a lot more appealing option than it was prior to the phone call.

And there are a lot of ways to reduce a boat's overall windage. Plus which, the benefits reaped by lightening the weight of the rig by so much probably more than make up for the extra drag induced by the larger rigging. Which, the stuff wouldn't be popular on the number of racing boats that it is if switching to it slowed the boat down overall.
Less weight aloft = reduced bouncing around of the rig & sails = better overall performance.

And bottom line, most serious racers would boot their wives or girlfriends out of bed for a month if it would let them cut 5lb off of their boat's weight aloft.
Okay, maybe a bit of hyperbole here. Say, 2 weeks, not a month

[estarzinger]

Originally Posted by poiu

Any thoughts?

three main ones . . .

(1) the conservative approach here is to size for equal stretch to your rod. Yea, that's going to be a big f&*king rope, but you will (probably) not lose your rig.

(2) regarding strength - realize you are going lose a significant fraction due to UV - there is some debate about how much, and it probably differs by rope, but lets just say ballpark 20% at 24 months. Since we are talking big diameter, lets say your wire exit stress rise will be 10% loss. So you are minimum 30% below new strength at 24 months. And you probably want to 'plan' for some further strength loss below that on things that would not effect the rod. So, I would say 40% below at 2 years to be 'safe-ish'.

Beyond matching the strength at some future point (like 24 months), how much stretching you want/can handle in your rig is sort of up to you. More stretch will both potentially fatigue the mast more, and effect sail shape in gusts.

Related to this - do realize that dyneema will not have the 'near infinite' life of conservatively sized rod (yea some insurance companies want it replaced every 10 years - but properly speced and looked after it will go for MUCH longer than that).

(3) Are you conversing with a rigger or NA or Oyster on this? You can DIY this, but if you screw up you can lose your mast.

Colligo do have a lot of experience with dyneema. I will comment that I have reason to believe that John Franta's (colligo's owner) technical understanding is not that strong (some of which were aired/debated in public on SA - if you want to judge for yourself), but that said, he is conservative and has a ton of experience and you (probably) will not lose your rig following his advice.

This is no longer a cutting edge application, and any decently competent rigger could help make sure you think it thru properly.

[UNCIVILIZED]

Originally Posted by estarzinger

three main ones . . .

(1) the conservative approach here is to size for equal stretch to your rod. Yea, that's going to be a big f&*king rope, but you will (probably) not lose your rig.

(2) regarding strength - realize you are going lose a significant fraction due to UV - there is some debate about how much, and it probably differs by rope, but lets just say ballpark 20% at 24 months. Since we are talking big diameter, lets say your wire exit stress rise will be 10% loss. So you are minimum 30% below new strength at 24 months. And you probably want to 'plan' for some further strength loss below that on things that would not effect the rod. So, I would say 40% below at 2 years to be 'safe-ish'.

Thoughts on chafe covers, & anti-chafe/anti-UV coatings assisting with lessening this degradation in strength?

Beyond matching the strength at some future point (like 24 months), how much stretching you want/can handle in your rig is sort of up to you. More stretch will both potentially fatigue the mast more, and effect sail shape in gusts.

Are you saying that with a mast designed to flex so as to be able to tune the main, that Dux will be a negative in this regard due to either:
- It's stretching more in a gust than rod would
- It being too stretchy to be able to well tune the mast in order to shape the sail in general.
And from what I understand, assuming the proper grade of Spectra (Dux) is used, then there's not much creep (or stretch) over time after the initial bits. Plus which if the stay gets too long, should you not simply be able to resplice it to a bit shorter length, re-prestretch it again, & then reinstall it?

Related to this - do realize that dyneema will not have the 'near infinite' life of conservatively sized rod (yea some insurance companies want it replaced every 10 years - but properly speced and looked after it will go for MUCH longer than that).

Thoughts on long term metal fatigue in rod near the ends? Some of it due to vibration causing micro-crystalization. Or is this bit of info incorrect, & if so, how.
Also, how much would you advocate trimming off of a rod backstay, if any, when re-heading it during a rig overhaul?

Obviously it's easier to make up for this resulting loss of length in a backstay than it is in say a cap shroud. So then on a (continuous) rod shroud, what would you advocate doing to them during a rig overhaul when it's time to re-head them to handle their being shortened? Since when you do this, the location of the bends where the rod passes over the spreaders changes. And there's bound to be work hardening in these spots/locations where the rod formerly passed over the spreaders, but it's now a "straight" section of the shroud due to the change in position caused by the shroud being shorter.
Hope that makes sense.

Yes, things can be X-rayed to look for problems, but... that isn't a foolproof way to spot problems. At least not as I understand it. And rigs that have undergone full overhauls, including having the important bits x-rayed, certainly have had failures despite such checks.

(3) Are you conversing with a rigger or NA or Oyster on this? You can DIY this, but if you screw up you can lose your mast.

Colligo do have a lot of experience with dyneema. I will comment that I have reason to believe that John Franta's (colligo's owner) technical understanding is not that strong (some of which were aired/debated in public on SA - if you want to judge for yourself), but that said, he is conservative and has a ton of experience and you (probably) will not lose your rig following his advice.

So then are you saying that he's perhaps lacking a bit in terms of depth of experience when it comes to some aspects of rigging with regards to knowledge of other rigging materials? And that some of the aspects of Dux rigging vs. metal (including rod) perhaps aren't as well thought out/engineered as they should be?

And yes, obviously no rigger can be a wizard on all types of rigging by any means. Plus which, compared to rod or wire, with Dux there's not the vast volume of knowledge & history behind what works, & what doesn't. Why, for how long, etc.

This is no longer a cutting edge application, and any decently competent rigger could help make sure you think it thru properly.

I'd surely love it if you had a heap of links to where some of us with less knowledge on these subjects than you could refer to in order to do some self-education on them.

And of course, thanks so much for sharing your knowledge, & experience on this stuff with us!


EDIT: A reference (or links) on "How to overhaul a rig rigged with rod for dummies" would be appreciated & then some. SIC
Ditto on such info on how to convert a rig over to synthetic rigging safely, from rod or wire.
Though yes, obviously, the theoretical knowledge on this stuff only goes so far. One also needs the hands on time with it, & time plus depth of experience with such things, in order to truly become a "journeyman" on such things.

[jfranta]

Evans, its a shame that your inherent need to insult people will limit your ability to be known as a major contributor to our industry. You even insulted Brion Toss who is more of a gentleman than everyone on here put together. Does it make you feel good to slam people on the forums really?

Originally Posted by estarzinger

three main ones . . .

(1) the conservative approach here is to size for equal stretch to your rod. Yea, that's going to be a big f&*king rope, but you will (probably) not lose your rig.

(2) regarding strength - realize you are going lose a significant fraction due to UV - there is some debate about how much, and it probably differs by rope, but lets just say ballpark 20% at 24 months. Since we are talking big diameter, lets say your wire exit stress rise will be 10% loss. So you are minimum 30% below new strength at 24 months. And you probably want to 'plan' for some further strength loss below that on things that would not effect the rod. So, I would say 40% below at 2 years to be 'safe-ish'.

Beyond matching the strength at some future point (like 24 months), how much stretching you want/can handle in your rig is sort of up to you. More stretch will both potentially fatigue the mast more, and effect sail shape in gusts.

Related to this - do realize that dyneema will not have the 'near infinite' life of conservatively sized rod (yea some insurance companies want it replaced every 10 years - but properly speced and looked after it will go for MUCH longer than that).

(3) Are you conversing with a rigger or NA or Oyster on this? You can DIY this, but if you screw up you can lose your mast.

Colligo do have a lot of experience with dyneema. I will comment that I have reason to believe that John Franta's (colligo's owner) technical understanding is not that strong (some of which were aired/debated in public on SA - if you want to judge for yourself), but that said, he is conservative and has a ton of experience and you (probably) will not lose your rig following his advice.

This is no longer a cutting edge application, and any decently competent rigger could help make sure you think it thru properly.

[jfranta]

See the stretch tables on our site for equivalent stretch sizing. We have done many SSB antenna's now that have been in service for 6 or more years, no issues. You do introduce a little more constructional stretch but if you use a turnbuckle or hyd adjuster it flattens itself out again. We use 16 gauge stranded, copper, tinned wire in a pvc sheath and prestretch to 2x the SWL of the application. Pre-stretching is important. Make sure to seal the buried end with some silicone or it will weep to the other end. We bring the lower end out in the bury portion of the spice. All the ones we have done have worked great.

We always use Brummel splices with 72x the diameter bury. If you do just a bury splice you need to whip it. And, we have all seen whipping come off. Brummels never need whipping. It is standing rigging so be conservative.

FYI, we just rigged a Saga 43 (second one we have rigged now) in Mexico and and the owner claims it heels 5 degrees less!

Originally Posted by poiu

I'm planning the big re-rig this off season. I am probably going with discontinuous rod throughout, replacing what is already there. It occurs to me that I could fit a dyneema backstay instead of the rod for the following reasons:

• The backstay is already highly adjustable by a large turnbuckle and a hydraulic ram, so any problems with stretch or creep can easily be dealt with.
• A re-do of a brummel splice would be possible on the back stay with the rig up, so again any stretch concerns can be dealt with.
• There is nothing to abrade the back stay or crash into it, so it is free from the damage the shrouds in particular potentially suffer.
• It is light and will save me about 28kg, mostly high up.
• It can (possibly) have an integrated internal SSB antenna in the form of a single PVC insulated wire of similar gauge to the copper in the GTO-15 and so save the extremely expensive cost of insulators in the rod of size -48.

Any thoughts on this?

I wonder if the heat from a transmitting SSB antenna would be harmful to the dyneema - how hot will a wire get?

Also, would the wire in the backstay cause a harmful stress riser as it exits the rope at the bottom end?

[jfranta]

Originally Posted by poiu

Thanks for your comments. You are prompting me on another important issue. I'm not sure there will necessarily be a lot of residual strength. As the force on the backstay is controlled by the hydaulic cylinder pressure it is possible to dial it down when not sailing, so reduce the loads and ensure there is no little term creep. To help further I was considering getting the Gleistein DynaOne HS Max. This rope is one of the new DM20 ropes that are emerging on the market. It has negligible creep and if sized to match the strength of the rod then there will be little strength headroom. Their 16mm rope having a breaking load of 23.5 daN and the Navtec -48 is 21.8 tons.

Stretch is a key factor. The dyneema with my 25.5m long backstay will have a stretch of 76mm at 10% load, whereas the rod has 17.5mm. An important question is how much stretch is OK in a backstay with a very stiff mast. To match the stiffness of rod I would have to go to massive sizes of dyneema, about 32mm diameter compared to the 14.3mm of the rod. About 4 times the breaking strength. Any thoughts?

All of the other Chemistries of Dyneema beyond SK75 have a considerable amount of constructional elongation when compared to SK75. This is why we still use SK75 heat stretched (Dynice Dux), and why Hampidjan and NER continue to use it. We have rigged over 750 boats now and have never had a Creep problem. Creep is a function of cross sectional area and just need to be designed for. The only time we really have to size for creep is high constant load applications like diamond stays on multihulls.

We would use our new 2 x 12 constructional 21 mm diameter dux for your backstay application. The large sizes tend to have more constructional stretch issues as the strands get bigger so we had them start using 2 x 12 construction for us.

John Franta, Colligo Marine

[estarzinger]

Originally Posted by jfranta

Evans, its a shame that your inherent need to insult people will limit your ability to be known as a major contributor to our industry. You even insulted Brion Toss who is more of a gentleman than everyone on here put together. Does it make you feel good to slam people on the forums really?

It's just the truth John, which I hope is helpful for fellow sailors to understand.

My comment about you above was (I thought) balanced - I did say the guy would (probably) not lose his mast following your lead, which he might do DIYing it. If someone is looking for practical knowledge and experience with dyneema rigging you are one of the short list I recommend, but if someone is looking for engineering or technical analysis you are not (and neither is Brion - while he is absolutely terrific at many other aspects of rigging and ropework).

Brion has since accepted what I said and we have moved on, and worked on things together since. (the backstory here is that years ago Brion was asked by a magazine to tech edit an article I wrote. He said to the editor that I was all wrong and that they should not publish it. I said back to the editor they should get a qualified engineer to tech edit it, and we agreed on a Harken engineer, who after a review said I was exactly right and the magazine published it. That was long ago, and we have done good work together on for example soft shackle development since - where his button is the one I recommend most).

I guess you never have, despite my going to significant personal effort (and expense) to test the issue in question in depth and to help you better understand it. (the back story here is that John challenged a best practice paper I wrote for US Sailing on dyneema lifelines. However John was wrong in his criticism; as he had, and continued for a long time, to miss-interpret or miss-understand bend radius strength loss in loops.)

I have moved on, am only doing rope work development for the heavy lifting industry now, where there is more activity and the consequences are higher, and thus professional standards are somewhat higher than in 'yachting'.

[poiu]

Originally Posted by estarzinger

(2) regarding strength - realize you are going lose a significant fraction due to UV - there is some debate about how much, and it probably differs by rope, but lets just say ballpark 20% at 24 months. Since we are talking big diameter, lets say your wire exit stress rise will be 10% loss. So you are minimum 30% below new strength at 24 months. And you probably want to 'plan' for some further strength loss below that on things that would not effect the rod. So, I would say 40% below at 2 years to be 'safe-ish'.

Thanks for your helpful comments.

2 years as a life target is way too low. It's going to loose a lot of attractiveness if I work on such a time scale. 6, or really 10 years is my target. I've seen charts predicting 10 years at 50% strength loss with dyneema, but I doubt I should reckon with such a large loss of strength on the thick rope I will end up with. Those figures relate to 8mm rope. I expect the process of UV damage is for the UV to attack the outer layers of fibres in the rope, reducing their strength to somewhat below 50% after 10 years, leaving the average strength at 50%. With thicker ropes the damage loss from the outer 2mm will be proportionately much less a reduction of total rope strength, so the safety factor that needs to be built in to achieve the working load limit at 10 years is going to be much less. I'd love to know what it is?

Originally Posted by estarzinger

(3) Are you conversing with a rigger or NA or Oyster on this? You can DIY this, but if you screw up you can lose your mast.

Yes I am using a rigger, but I realise I will be taking the risk on my shoulders. The CYA culture rules supreme. I'm going to take all reasonable precautions.

Noting your thoughts elsewhere on the importance of bend radius, Sampson are recommending a 3X bend radius. Is that enough, or should I push it up to 5x?

[poiu]

Originally Posted by UNCIVILIZED

You should call, repeat, call, Colligo Marine & discuss this with them. I had an OUTSTANDING chat with the head of the company recently. Concerning, ironically, switching from rod to Dux. And he was more than pleasant to talk to, & went way above & beyond to field all of my questions. Some of them quite technical, due to my extensive involvement over many decades, with what makes boats & rigs "tick".

Dux gets sized to match up (or well exceed) the stretch of the metal rigging that it's replacing. So in terms of overall diameter, yes, your backstay will be quite a lot thicker. But given my chat with Colligo, going to synthetic rigging is a lot more appealing option than it was prior to the phone call.

And there are a lot of ways to reduce a boat's overall windage. Plus which, the benefits reaped by lightening the weight of the rig by so much probably more than make up for the extra drag induced by the larger rigging. Which, the stuff wouldn't be popular on the number of racing boats that it is if switching to it slowed the boat down overall.
Less weight aloft = reduced bouncing around of the rig & sails = better overall performance.

And bottom line, most serious racers would boot their wives or girlfriends out of bed for a month if it would let them cut 5lb off of their boat's weight aloft.
Okay, maybe a bit of hyperbole here. Say, 2 weeks, not a month

Thanks for this. I have spoken to John in the past and he was helpful, but he couldn't help with a full re-rig. Dyneema rigging can't do the discontinuous rigs in big sizes. I don't understand why. I put it down to not enough market to justify the risk in developing it, but I don't know.

I agree lighter rigs are great, especially in racing boats or especially dinghies. I am doing it as part of an exercise in diet all round, plus there are other big advantages. No isolators. They cost nearly $4000 on my boat and I'm not sure I can even buy them now as Navtec are bust. I'm hoping with the fact that I can unload the rig when in the dock or storage that I can get a really long life out of it.

I'm not sure I can reduce the windage though anywhere without removing the bimini and going for a roll up dinghy instead of one on davits, compromises I'm not ready to make.

[poiu]

Originally Posted by jfranta

See the stretch tables on our site for equivalent stretch sizing. We have done many SSB antenna's now that have been in service for 6 or more years, no issues. You do introduce a little more constructional stretch but if you use a turnbuckle or hyd adjuster it flattens itself out again. We use 16 gauge stranded, copper, tinned wire in a pvc sheath and prestretch to 2x the SWL of the application. Pre-stretching is important. Make sure to seal the buried end with some silicone or it will weep to the other end. We bring the lower end out in the bury portion of the spice. All the ones we have done have worked great.

We always use Brummel splices with 72x the diameter bury. If you do just a bury splice you need to whip it. And, we have all seen whipping come off. Brummels never need whipping. It is standing rigging so be conservative.

FYI, we just rigged a Saga 43 (second one we have rigged now) in Mexico and and the owner claims it heels 5 degrees less!

That's good information, thanks. I can't see my heel angle being reduced much. That Saga 43 must be an unfeasibly tender boat if it reduces heel by 5 deg unless it is measured at extreme heel angles, but I suspect you don't believe it either in a practical sense.

Originally Posted by jfranta

All of the other Chemistries of Dyneema beyond SK75 have a considerable amount of constructional elongation when compared to SK75. This is why we still use SK75 heat stretched (Dynice Dux), and why Hampidjan and NER continue to use it. We have rigged over 750 boats now and have never had a Creep problem. Creep is a function of cross sectional area and just need to be designed for. The only time we really have to size for creep is high constant load applications like diamond stays on multihulls.

We would use our new 2 x 12 constructional 21 mm diameter dux for your backstay application. The large sizes tend to have more constructional stretch issues as the strands get bigger so we had them start using 2 x 12 construction for us.

John Franta, Colligo Marine

When looking through the Gleistein catalogue they give the stretch at .3% at 10% load for all of their SK78 and DM20 Heat Set products and using that figure it can be easily calculated against the Navtec catalogue what the equivalent stretch is in rope to steel, yet in your website's stretch matching guide it gives equal stretch of steel rigging to ropes that correspond to much lower thickness than I calculate with. Dux is heat set and pre-stretched like SK78/DM20 and of higher stretch in fibre. Can you explain all that?

I looked at Gottifredi Maffioli's catalogue and they give a lower stretch for a given rope diameter the higher the grade of dyneema, so an SK75 being more stretchy than SK 78 or SK90. I don't understand why you say your SK75 has a lower stretch?

SK75 should also have a much lower creep than the other grades. Is that not an attractive attribute?

Why do the finer fibres of the 2 x 12 improve the constructional stretch?

Also what is meant by constructional stretch? I would have thought that the constructional stretch is virtually eliminated after pre-tensioning and heat setting and that nearly all that is left is the fibre/material stretch. Is that not so?

[estarzinger]

Originally Posted by poiu

UV . . . . . thick rope

Do realize that (in a single braid, because of the way they are braided) ALL the fibers do end up at the surface of the rope at some point and are all UV exposed, even on thick rope. So they will all get damaged (eg rope thickness does not really matter much on this factor with single braids).

so the safety factor that needs to be built in to achieve the working load limit at 10 years is going to be much less. I'd love to know what it is?

I just saw the results of a 10 year assessment/pull test (we are just now getting a decent sample of 10 year experience) with various 20mm dyneema single braids - and there was a pretty wide spread in the results (between 30% - 70% strength left, the specific rope models have mostly now either been replaced or modified - but the results should be generally in the ballpark with current product) but 50% would be a rough benchmark. Trying now to understand why the spread was so large.

Noting your thoughts elsewhere on the importance of bend radius, Sampson are recommending a 3X bend radius. Is that enough, or should I push it up to 5x?

I agree with samson.

Also what is meant by constructional stretch? I would have thought that the constructional stretch is virtually eliminated after pre-tensioning and heat setting and that nearly all that is left is the fibre/material stretch. Is that not so?

You will have initial stretch both from your splices and constructional stretch. There is still constructional stretch left in heat set rope - even wire rope has constructional stretch. You can in theory pull almost all this out by splicing it and then pulling it hard before you rig it - but with the size/strength rope you are taking about, I'm pretty sure you will not find the facilities to pull it hard enough in the Caribbean - In the US or UK you could do it at a certified testing facility (they all have huge calibrated pullers).

...............
btw sorry to distract your thread with that detour above, was not my intention.

[Jesse]

You have an interesting project. The only problem that I can see is the possibility of snapping the copper core if the antenna is attached to the masthead. due to the creep of the Dyneema. A loop or coil in the antenna wire once it exits the back stay core might handle that but loops and coils detract from an antenna's performance. You've a great idea here please keep us posted.