Hey everyone... I've been away for awhile but I do check in on ocassion. I'm currentley rigging a 56 ft John Alden ketch in full synthetic, 22 total shrouds/stays with running backs and associated parts. Large boats use turnbuckles (5/8" on the main, 1/2" on the mizzen), but there is still lashings for 30 to 50 cm above the turnbuckle to absorb creep over time. The Mains are 11mm sk 78 and the Mizzen uses 7mm, I use a full dyneema chafe sleeve cover on every shroud, every time.
Yes, size dyneema for creep, not stength, that is usually 1mm larger in size than the orginal wire and tends to be at or above 2 times stronger in tensile than the wire was. Always use heat annealed Dyneema or you will have headaches for quite awhile. I used 3mm STS HSR on my C22 which is esentially the same zize as the 1/8 wire, but if you put calipers on the 3mm STS HSR it is actually 4mm (which explains why the published tensile strength from NE Ropes greatly exceeds the specs for all other 3mm Dyneema from other manufacturers). Anyway, I believe that the creep from the sail loads on a C22 would be so minimal that the creep would have a hard time catching up with the available tensioning distance of the turnbuckles. I really can't calculate that to any point of assurance without knowing what the actual loads will be and at what interval. I've already spliced by forestay and my backstay in 5mm just because I could. There is also the option of stepping up the turnbuckle size to 5/16 just get a bit more tensioning travel. I haven't fully tested any of this yet, I've been far too busy rigging bigger boats. Please note, on all customer boats to date I have used Deadeyes alone with generous lashings or turnbuckles with lashings, I have never suggested a direct shroud to turnbuckle connection and niether would any other responsible rigger. My THEORY is that small boats and racing dinghys can get away with it.
As was mentioned before, splicing Dyneema and then pre-stretching it to land on an exact eye-to-eye measurement is very tricky. I use a complicated spreadsheed that calculates this for each line size I use. Once you establish a baseline and you are consistent with your splicing technique you will get accurate finished lengths to within a few mm every time. It becomes even more complicated when splicing a full cover on the line that also covers the eyes as well. I don't do this to match the eye-to-eye of the wire and then direct connect to the turnbuckle, I do it to have a consistent length of lashings no matter if I use a turnbuckle or a Deadeye alone. There would be few things worse than looking down either side of your boat and seeing all kinds of skewed lengths of lashings!
BTW, what makes the turnbuckle use possible with lashings to Dyneema shrouds is the Colligo Male Chainplate Distributors. They pin to top toggle of a Jaw/Jaw turnbuckle and form the bottom of the short Deadeye. I don't use the Colligo Terminators in the lower eye of the shroud, they are too expensive and they have alot of friction. I use my HD stainless thimbles that actually have a larger bending radius on the lashings than the Colligo terminators and cost WAY less. (No, I don't sell them to the public). I buy my Colligo parts from P2Marine (google them), they are just bit less there than the advertised prices on Colligo's site. I don't get any special discounts, when I get them for customer jobs I only charge what I pay, I don't mark them up.
Two HUGE things you have to consider when using Dyneema rigging... Your spreader tips and other mast connection hardware. The 'stock' tips of the C22 are a no-go, they would shred the cap shroups eventually. You need some sort of solid tip where the groove is very smooth. I had some delrin machined by Stingy Sailor, they can also be aluminum as long as they have a nice chamfer and are sanded smooth. You skip the wire siezing and lash them in with something like Samson Lash-It or small diameter dyneema kite-line, anything 1.5 to 2mm is good. Second is mast harware... the C22 is good to go here. Everything is pinned intoplace with standard double tangs or 1/4" pins through the masthead. Other boats that have either stemball fittings or T-bails will have issues, however some significant progress is being made in the industry with adaptable hardware or fittings.
Anyway... if you have any questions let me know. I'm on FB under Kraken Structures or search "Sea Monster Strong"
