In order to minimize the strain on our anchor, we expect the rode to absorb impact forces imposed by waves, yawing and gusts. These can be as much as five times the average load based on Practical Sailor and ABYC testing. Chain does this through the effect of catenary and resistance to being dragged side to side across the bottom, if the water is deep enough that the mass of chain deployed is enough. Nylon does this by stretching as much as 3 to 4% in length at 10 to 12% of breaking strength, which is the practical working load limit (WLL) if you want a long life. This amounts to 3 to 4 feet if 100 feet are deployed. If less than 100 feet there may not be enough stretch. The polyester single braid recommended for anchoring stretches just less than half as much, about 1 to 2% at 10% of breaking strength. But before we summarily dismiss it as unsuitable, there are several things to consider.
This was a helpful and informative article. You offered lots of technical detail.
But, and maybe I missed it, I didn’t see anything on recommenced service life polyester and nylon. Although service life is mentioned qualitatively, you didn’t say how many years, even as a range.
We bought our boat used so we have no idea about the age of our anchor rhodes. Could you offer some recommended service lives for each material, likely for saltwater and freshwater environments? We are on the Great Lakes but I suspect others would be interested in service life recommendations.
Thanks,
…..Ed
The problem is that rope does not age sitting in a closet at home. I’ve tested 30-year old climbing ropes that still tested like new, both strength and dynamic characteristics. They don’t age much more than that in a locker. Salt matters little, not just sitting. It is all about load cycles, UV exposure, and abrasion.
UV. 3 years is about the limit for nylon in sun, losing about 10% per year (depends on latitude and color). As a dockline it can last longer, if it is over strength. But how much sun does any given section of rode see? It is not exposed in the locker and not underwater, so only a 15′ section from locker to water, and not always the same section. Probably not a big deal unless you live on the hook.
Cycles. Load cycles in fair weather don’t really matter; they are too far below the WWL. Storms on the other hand count a lot, but much depends on exposure and duration. Certainly many, many dozens of strong thunderstorms, a dozen or more sustained storms (nor’easter), and maybe one tropical storm you barely survived. Again, I am speaking about nylon; polyester is about 5 times more fatigue resistant.
Abrasion. External cafe is relatively easy to gauge. Sand and rocks will do more, mud much less. Internals chafe is trickier, but if the rope is much stiffer, that is a clue. Washing or adding certain treatments (water repellents or fabric Softener will limber it up but NOT undo the damage.
The bottom line is that a nylon a rode can last 2-20 years, depending on use. I don’t believe there is any such thing as typical use. Dock lines and halyards are different; we know own much sun they get and we know the tugging is constant.
If the windlass has a combination rope & chain gypsy, then the best anchor rope is the one that fits the gypsy. With a proper rope-chain splice, 8-plait nylon backing up chain is an excellent, practical, and very safe on a combination gypsy. 8-plait nylon does not hockle so easily as 3-strand, has some stretch but not as much as 3-strand, and is much lighter than chain. Notably, 8-plait nylon does not unwind when stretching, and rewind when contracting. This unwind-rewind of our old 3-strand made a mess of snubbers and a lot of clunking noises at night. 150′ of chain + 150′ of 8-plait nylon worked well for us when full-time cruising and anchoring a lot.