Splicing rope to chain

Recent windlass models have all sprouted chain sprockets (wildcats) with a groove at the bottom of the chain teeth to grasp the rope part of a combination rode. The idea of a special groove to grasp the rope is not newself-tailing winches have had them for years.

But there the analogy ends, for on the self-tailing winch the load is carried by multiple turns around the drum before it is tailed into the grooved cap. The wildcat’s groove, however, must carry the full rope tension during the weighing of the anchor, something that must not be overlooked.

Until a few years ago, the grooved wildcat was seen only on Simpson-Lawrence windlasses, and the broader opinion prevailed among other manufacturers that it wasn’t a suitable method to haul in on the rope part of a combination rode. Actually, the dichotomy in thought arose from the fact that the Simpson-Lawrence patent stood in the way of other manufacturers’ incorporating the idea into their windlasses. Now the patent has expired, and many windlass makers are offering special grooved wildcats.

The combination wildcat requires that the rope groove have angled ridges (whelps) capable of firmly gripping the rope, similar to the self-tailing winch. In operation, the wildcat groove hauls first on the rope portion of the anchor rode until the chain portion arrives, then the wildcat’s sprocket grasps the chain links and completes the weighing of the anchor. To effect a smooth operational transition between rope and chain, the rope has to be spliced directly to the chain in place of using the conventional thimble, eye splice and shackle connection. Herein lies the latent problem, because splicing rope to chain has always been a questionable practice.

Mariners should be aware that sharp bends in a rope can weaken it significantly. To get the maximum life (and reliability) out of rope, it should not be bent over radii less than several times the rope diameter. Obviously, the result of bending it over the small diameter of a chain end link is the antithesis to long life and dependability.

Nevertheless, the customer has eagerly accepted the concept because of its convenience. The grooved wildcat is certainly a smoother and safer way of retrieving a combination rode than having to transfer a bulky shackle and eye splice from warping drum to a conventional wildcat, but how reliable is the technique? Strength and longevity are the issues at hand. Strength can be measured, but longevity is a measure of time in use.

Some splicing options

There are (at least) three different ways to directly join rope to chain. One is the three-strand eye splice, which has three variations in itself. There is also a two-strand splice (made with three-strand rope) and a four-strand splice (made with three-strand or eight-plaited rope). All have their pluses and minuses.

The three-strand eye splices all have the same drawbacka 60% increase in diameter at the splice that can cause the splice to walk out of the wildcat groove during transition. The result is an annoying disengagement that becomes more noticeable as the splice ages and becomes hardened through an accumulation of salt and mud in its strands. I’ve experienced this with an early model Simpson-Lawrence single-grooved wildcat. Simpson-Lawrence has alleviated the problem in its later-model wildcats by having a wider groove cut above a narrower groove to accommodate the splice bulge with the narrower groove below it to tail the rope. The two-strand splice is an anomaly because it removes one of the three strands, yet has a slightly greater splice strength than the three-strand splices. At first blush one might think that a two-strand splice would be significantly weaker than a three-strand splice, but the two-strand splice is actually carrying its load through four strands, two on each side of the chain link. This is one more than the parent rope. With that argument, you could say that the three-strand splice should be able to carry double the parent rope’s load. Unfortunately, the sharply bent, crowded, and unevenly loaded strands passing through the chain link appear to be strength-limiting factors. The two-strand splicing technique creates only a 25% increase in diameter, something we have learned to live with when making a long splice in running rigging that has to be able to run unimpeded through rigging blocks. The smaller splice diameter also allows the two-strand splice to nestle itself into the single wildcat groove.

The four-strand splice is a bird of an entirely different color since it does not double back on itself and, therefore, does not weaken its own strands, nor does it increase its diameter a measurable amount. It is best suited to eight- or 12-plait rope, but can be made in three-strand rope. Its ability to carry the anchor load depends on friction between the four rope strands and the consecutive chain links through which it is woven. No test data is available on this splicing concept, but the writer is aware of its successful use in a number of instances, including 14 years’ service on one boat embracing a Hawaii-to-Tahiti cruise.How strong the splice?New England Ropes has conducted strength tests on rope-to-chain splices using accepted testing equipment and procedures. The results are summarized in the accompanying table in terms of splice efficiency, which is the ratio of the breaking strength of the spliced element to that of the non-spliced (parent) rope. Also noted in the table is the increase in rope diameter at the splice.The three-strand direct rope-to-chain splice tests were made with 1/2-inch rope spliced to 1/4-inch chain and 5/8-inch rope spliced to 5/16-inch chain. The test results using the tight unthimbled eye splice and the Simpson-Lawrence splice described in the sidebar showed an average 85% strength efficiency. While neither was as strong as a thimbled eye splice, the average efficiency is seen to be the same as that of a conventional rope-to-rope short splice. There were breaking strength variations between test specimens, as would be expected due to splice-making quality. The snap-shackle splice was not tested.

Tests on two-strand rope-to-chain splices using the same combinations of rope and chain showed them to be slightly superior in strength efficiency to the three-strand eye splices for the reasons discussed previously. Like the three-strand splices, this splice is not as strong as the conventional thimbled eye splice, but it does equal the strength of a conventional long splice indicating it to be a reasonable splice for joining rope to chain in a combination anchor rode.It should not be surprising that rope-to-chain splices are less efficient than well-made thimbled eye splices, for they violate a most basic tenet of rope applicationsthe allowable minimum bend radius. Rules of thumb for minimum bend diameters for maximum durability have evolved over the years and have been verified by testing. Dynamic applications as in running rigging call for a minimum sheave diameter approximately eight times the diameter of the rope. Static applications as in a thimbled eye splice (or around bitts, fairleads and chocks), call for a minimum bend diameter of three times the rope diameter. In all of the direct rope-to-chain splices, individual strands are bent 180° through a chain link that presents a frighteningly small, almost one-to-one bend diameter. Furthermore, the strands of the rope follow disparate paths through the chain link, and it is unlikely that they are very evenly loaded. It is believed that a good snap-shackle splice may even out that problem.

That’s the bad news; now what is the good news?

It came as a surprise to many (except, possibly, Simpson-Lawrence, which pioneered the wildcat groove idea) that these rope-to-chain splices were so strong in these basic, one-dimensional static strength tests. It is too soon, however, to draw final conclusions based only on these tests because splice durability under cyclic loads and environmental degradation are totally unknown. Those two factors may well overshadow pure static strength in determining the long-term value of these splices in their ground-tackle role. A boat owner using any of the rope-to-chain splices described here should weigh its convenience against the possibility of a rode failure that could place his or her boat in jeopardy. On the basis of these tests alone, one can say that the rope-to-chain splices tested are equal in strength to their basic splice pattern (short or long), but none are as good as a properly thimbled eye splice. It would also be safe to say that their durability (especially compared with a thimbled eye splice) is still in question and we need more field data.

Categories: Navigation