The recommended standing rigging change interval is as far as I have read 10 years. Many insurance companies will not insure a yacht with an older rig, or they ask a high premium. Our rig is approaching 20 years, but I have found no visible signs of wear. We crossed the Atlantic back and forth without worries with it when it was 15 years. However, experts point to the fact that you can not know the condition of swaged terminals, as they can not be inspected inside.
I believe the marine industry (and many others) keep maintenance and inspection intervals short to boost business. So, after careful consideration, inspection and googling, I usually have noe fear doubling the time for many products.
Well, for the rig we are almostat at the double point now. We plan to use the boat for many years to come, fate permitting. Therefore, now would probably be a good time to change it.
As the multihull society is often rapidly catching up with new trends and products, I have of course read and heard about synthetic rigging. With its many advantages. And relatively little cruiser knowledge and experience. There are disadvantages too. But it sounds exciting.
After quite a bit of checking, I decided to give it a try. The cost savings would not be very large, due to several factors. Firstly, a riggers company would give a total price for a total job of installing a new stainless steel rig. I need a roller furling stainless steel forestay, so I had to go there anyway to have that done. Further, I do not have a solution for the diamonds in a synthetic version. I will have to wait, or have that also done by the riggers. And I wanted to buy a spare lenght of upper and lower shroud in case of miscalculating a splice. If all splices were successful, I would have cruising spares. They are light and fairly easy to stow.
The rope that is commonly used for synthetic rigging to date is SK75 dyneema, the prestretched and heat treated version is called Dux. There is information in the Colligo Marine website about rope and splicing.
The most difficult part for me was the calculation of the spliced shroud lengths. Most of the projects I have read about use lashings to tighten and adjust the shrouds, but for larger boats and heavy catamarans I read that turnbuckles are recommended. Turnbuckles are also fairly easy to adjust and you get an immediate impression of tensioning. But when using turnbuckles, the rope has to be spliced to a minimum and maximum lenght that is not within a large tolerance. Factors of uncertainty are how much the splices will shorten the rope, how much the splices then will restretch when tensioned, how will it be possible to prestretch properly, how much will the dyneema stretch when installed and tensioned?
Dux Dyneema is not unstretchable, it just stretches much less than other ropes. Like wire, which also stretches when pulled hard.
A technique that worked fairly well was to mark a point a distance (for example 2.5 meters for 15mm Dux) from the bitter end, when starting the first splice, that would be just outside the splice when the splice was finished.
Then use this calculation, after prestretch, to calculate where to cut the rope before starting the second splice.
For the prestretch I bought a 4 ton ratchet puller. A concern about such a puller is how easy is it to get 4 tons pulling power out of it? The 15mm Dux I pulled hard enough to break a cord or two due to friction in the reel (should have oiled it?). Still I have the feeling it was not quite enough.
I found some solid mooring points in a harbour in Oslo that I could use for the stretching.
After the prestretch of the first splice of all the lines, I knew where to cut them to achieve the desired length, using the exactly same splice. With the exception of one upper shroud, which ended up a bit longer than target, it seemed to work out well.
The splices themselves are not so complicated, I followed Colligo Marine's instructions, and did some test splices on smaller dyneema ropes. The fids required are maybe not the most common sizes, but it is easy to make DIY versions. I used some copper and steel scrap tubes, and fitted them with wooden tips as shown below.
For the 15mm rope, I found a heavy duty solution for the most demanding part of the splice:
The rigging hardware is another area that needs a lot of planning. As thimbles are used in both ends of the ropes, not all products are useable. My previous system, ACMO, was not suitable. Nor were many others. The turnbuckles with forks and toggles would have to be wide enough to accept heavy duty thimbles. And also fit my chainplates. Upper mast connection to a thimble was also a challenge. The final solution was equipment from Blue Wave and some heavy duty shackles from Peterson.
The reason for using standard heavy duty thimbles is availability and price. I suppose it might be easier to find rigging parts using Colligo Marine terminators, designed to accept clevis pins. But I have not dug into that. Shipping and import taxes would rise the prices to unpleasant levels.
Colligo Marine tables and information were also used for the rope dimensions. As is common, the original rig wire specifications will be the reference for the stainless steel hardware. But for the ropes, a factor called creep will be dimesioning. Creep is something else than stretch, and when using the tables, one will find that the correct rope will have a larger breaking load than the original wire.
According to Murphy's Law, there will be surprises and setbacks when installing marine hardware. I knew that the clevis pins of the original rig were metric sizes. The new ones were imperial inches. Therefore, a slight widening of holes in the chainplate and mast fixing points were necessary. Easy match, I thought. But Marechal really had put some tough steel bushings in their mast. Dangling from my bosuns chair, sweating and cursing, I devastated my 19mm drill bit widening the holes from 18mm.
One detail that I have tried is to fit a simple 2 meter plastic tube, meant for electric cables, as lower end chafe protection. It must be installed before the second splice. Thus it can not be replaced. I do not know the UV Properties of such tubes, but they are cheap and worth the experiment. In addition there will be canvas chafe protection around the lower splices.
The ropes are now installed. Time will show how they will stand up to cruising demands. There are a few factors that are surrounded by some uncertainty for cruisers.
Obviously, as stainless steel has dominated totally for many decades, chafe will be on the list. According to the user experience I have read, the ropes will become a bit "furry" with time and UV influence. But they will be dimensioned structurally much stronger than stainless steel, and even some chafe will not weaken them substantially. I will try to avoid chafe the best I can.
Then there is hum. Some users report some humming from synthetic rigs, but it is not regarded as a problem or nuisance. We were quite scared when installing the upper shrouds. The mainsail dyneema halyard was used to support the mast while changing. It hummed like crazy. My wife looked at me in disbelief. Will it be like this? Fortunately not. There was no sound after installing the synthetic shrouds. But as we just recently have finished the rigging, we do not have experience from any length of time.
Report from june 2019: We do experience some more hum with the new rig. Obviously, as the wind picks up, there will be noise from all sailboat rigs. And from different parts of it. The wind hum now starts a bit earlier, and has a bit more bass to it than previously. But I have always had the feeling that there is more wind than there actually is when listening from the cabin, so the difference is not that great.
What will happen in case of a lightening strike? Will the ropes burn? I have heard of no occurences, time will come up with user experience somewhere. Meanwhile, since we have a stainless steel forestay, I plan to install a copper cable from the seagull striker back to the chainplate. It will then hopefully work the same way as before. The chainplate is connected to the sea via the Dynaplate. Probably the same system on all Privilege yachts.
I do not know if insurance companies will object to synthetic rigging for long distance voyaging. Another issue may be the fact that you can probably not pop by any riggers shop and get a rig inspection and certificate? My impression is that not many places have this expertise.
On the side of positive bi-effects, weight savings is probably not enough to impress owners of fairly heavy Privilege's. The new rigging is approximately 20 kg lighter than the old system. For a catamaran, the fact that it is weight aloft is probably not as significant as on a monohull. The weight difference would have been larger if using a lashing system instead of heavy turnbuckles. But as I have already tightened several times, I am happy with a system that makes adjusting fast and easy.
Update July 2019:
During installation of the rigging lines, it seemed that the longest upper shroud might be too long, depending on how much it would stretch and elongate in the spliced areas. This assumption proved to be right. I ran out of turnbuckle travel. Fortunately a shorter spare had been produced before leaving harbour for the summer, and it replaced the long one in mid july.
So now I have some new views on the prestretch procedures commonly distributed on internet blogs and discussions. My experience leads me to believe that the recommended short prestretch to the applicable value is not sufficient. It appears that the splices need to be stretched over some more time to settle permanently. The difference is significant. I tightened the turnbuckles almost as much as I could with a spanner. Only hours later I was easily able to tighten some more turns. The next day even more. A few days later more. A week later some more. Totally estimated 2-3 inches for my upper and longest shroud.
This would not be a problem with a lashing system dimensioned for some stretch. But again, lashings are not recommended for larger boats, and the frequent adjustments are cumbersome compared to turnbuckles.
If I had this knowledge when starting the project, I believe I would have had 2 options to get it right. The more unrealistic one would be to leave the lines in stretch for many days, reapplying tension successively. I do not know how I could have achieved this. Thus I would instead have made the splices 2-3 inches shorter, and used some rigging toggles to lengthen the shrouds temporarily. Most probably the toggles could have been removed after some weeks of sailing. If not, given correct dimensioning, they could have stayed in place for a longer period.
Udate end of first season:
After the summer and a lot of sailing, the shrouds seem to have stabilized. But not before the lower shrouds are almost out of travel too. Still some tightening is possible, but I would have liked it to be much more. The tension will be released on all lines as soon as the boat is in the winter harbour. Thus the creep will be minimized.
Also, the plastic tubes intended as extra chafe protection were not a success. They are not fitted tightly, and as soon as there is vibration in the lines, the hum is amplified by the tubes. I have to be very careful not to damage the dyneema when cutting them away, thus this far I have only been able to remove the two largest. For the inner forestay I think I will need some other plastic chafe protection, as the genoa and its sheets are often flying over it at high speed and pressure when we tack. But I will try to use the old fashion split tubes that cling more to the stay. There is another problem with that solution however, a stormsail with metal hanks will probably chew up the plastic quickly. So a softer solution is needed. Dyneema softshackles is a possibility, but hanking the sail on in bad weather will be cumbersome. Then again, it is recommended to have the stormsail ready and hanked on when on longer passages.
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