What size dyneema for 30' cruiser standing rigging?

[zachduckworth]

Hi,

I have a thirty foot 1984 Islander Bahama. It is decidedly a cruising boat and that's why I use it for. The boat is in SoCal and she may end up in the Sea of Cortez someday (let's hope it's sooner than later..).

I am replacing her sixteen year old 1x19 with synthetic. I am going to use lashings to tension the stays for now. If I hate doing it I'll get turnbuckles but for now I want to experiment a bit.

I am planning on using Colligo Dux for the standing rigging because it seems like it requires less work to get all the initial stretch out, they have an excellent reputation, and because the cheaper alternatives are either not actually that much cheaper or else have a bunch of severe negatives that make them either unsafe or a lot of extra work.

My boat comes spec'd for 7/32 1x19. Breaking strength is 5550 lbs. Dyneema is sized for stretch not breaking strength. That said, the equivalent for stretch for 7/32 is about 5.5mm on the Colligo chart. Of course, they don't have that; the nearest sufficient-for-stretch rope they make is 7mm. It has a 3000 safe working limit and a 16,000 lbs break strength. My shrouds are kept at about 15% of break strength, forward lowers significantly less. The forestay and backstay are at about 15, and the cap shrouds as well. That's about 832 lbs.

When I spoke to Colligo awhile ago they recommended sizing the shrouds at 9mm instead of 7mm to provide more margin from stretch. They explained that this benefited cruisers but I didn't get a full explanation on that. The max break strength of 9mm Colligo Dux is 26,000 lbs, which is pretty well overspec'd for a boat that runs 7/32 1x19.

The 9mm Dolligo Dux is significantly more expensive than the 7mm. It is also very thick; it is the size of some of my mountaineering ropes (I know that's apples and oranges, but still). At that price difference, I am wondering if I would be better off with a cheaper 9mm dyneema and dealing with the stretch, or if 7mm is plenty fine?

For context, a quick bit of online window shopping shows the following options:

200' of 9mm CD is $1236.0.
200' of 7mm CD is $852.00.
200' of 3/8 AmSteel Blue is $530.
200' of 7/16 AmSteel Blue is $644.00
200' of 1/2 AmSteel Blue is $698 to $990 depending where you buy.


Note that 3/8 Amsteel Blue has the same break strength as 7mm CD. But the 7/16 might be in a sweet spot. That said, in my experience with my Amsteel lifelines it has stretch for days... but that eventually disappears, of course. I have seen some online opinions say that CD is overkill for a boat my size and temperament.

What do you all think? Does it make sense to go for CD, or AmSteel or something cheaper (but not generic)? What size makes sense here?

[SailFastTri]

I tried using Amsteel rather than DUX on a 40’ trimaran. The conformal stretch was so bad I lost room for lashing adjustments and had to re-splice twice in the span of a few months. First for conformal stretch, then for creep.
That boat also had full battens and swept back spreaders, so there was inevitable contact between the mainsail and shrouds which caused fuzz on the dyneema. That would have been disconcerting on an ocean crossing (if that’s in your plans).
I suggest you go with DUX and take their sizing recommendations. They’re the experts on this and it’s what they do. If you don’t use DUX use steel. Don’t cheap out you may regret it. And don’t use Chineema.

[s/v Jedi]

Why do they recommend 7mm in writing but 9mm over the phone? Sounds like a salesman going for higher commission… 9mm has less creep? Sure, why not 12mm?

[markxengineerin]

It's not a black and white task to "size dyneema for equivalent stretch as steel". At what temperature? At what strain rate? At what load? How old is the dyneema/how degraded is it? I imagine all of these things affect the stiffness of dyneema order(s) of magnitude more than steel.
I got my Dux from Colligo, and same experience, they were suggesting the next size up vs. the website. It is a difficult business to be in, selling a product that is not yet 100% understood to customers who will possibly mis-use it vs. your recommendations. I can see the verbal recommendations being more for reasons of "conservative design = smart for cruising boats" than greed.
That being said, I would go with the 9mm and turnbuckles if you must go with Dyneema. It's going to creep, but you'll have less to deal with and a quicker and easier time adjusting it that way.

[Randy Bogardus]

Originally Posted by markxengineerin

It's not a black and white task to "size dyneema for equivalent stretch as steel". At what temperature? At what strain rate? At what load? How old is the dyneema/how degraded is it? I imagine all of these things affect the stiffness of dyneema order(s) of magnitude more than steel.
I got my Dux from Colligo, and same experience, they were suggesting the next size up vs. the website. It is a difficult business to be in, selling a product that is not yet 100% understood to customers who will possibly mis-use it vs. your recommendations. I can see the verbal recommendations being more for reasons of "conservative design = smart for cruising boats" than greed.
That being said, I would go with the 9mm and turnbuckles if you must go with Dyneema. It's going to creep, but you'll have less to deal with and a quicker and easier time adjusting it that way.

I rerigged my Storfidra 25 with Colligo DUX and used lashings. As far as dealing with Colligo and John Franta I agree 100% with markx.

[Benz]

I have 7mm heat-set DM20 on my 31' boat, and don't wish it any bigger. My opinion (minority report, I know,) is that 7mm DUX will be fine. Pre-stretch the splices between two trees with a come-along on a Spanish burton and they'll be pretty stable once onboard.
Use 3/16" SK78 for lanyards, tighten the fall with a come-along hung from a non-stretch halyards, and go sailing.
I wouldn't use anything other than DUX or DM20 MAX for standing rigging, unless it was Maffioli Ultrawire.

[s/v Jedi]

About tightening the lashing: pulling down is more efficient than pulling up. The trick is to tie a temporary low friction ring in place at the exact right position in line with the lashing when pulling aft towards a primary winch in the cockpit. The ring needs a line to a strong point forward as well as down to the base of the lashing.

There are multiple good videos showing the technique on YouTube. Tula Sailing and the Rigging Doctor are two I remember.

I recommend the book from Dedekam on rig tuning as well. It isn’t about Dyneema rigging but it shows how the mast should be trimmed and how to achieve that. You need this info and complement it with info specific to Dyneema.