More marlinspike seamanship
Posted on 29 April 2009
Written by Mike Saylor
Marlinspike seamanship keeps coming up because it’s so important.
It separates the men (and women) from the boys (and girls). It’s important to know about rope and its construction, even if you don’t make your own splices. Every boat uses rope — or line, when it has a purpose on board.
1. Rope construction
• Laid line is the most common, and likely the oldest, type of rope. Hawser laid rope consists of three strands twisted together clockwise as you look down its length. Properly constructed of the appropriate material, it’s easy to splice and repair. Because it stretches under load, it is excellent for anchor rode and dock lines, where its elasticity acts as a shock absorber. On the downside, it tends to hockle and kink if not handled properly. Always coil laid line from right hand into left.
• Braided line can be a single braid and may be solid or hollow. You can’t splice solid single-braided rope, so it serves little purpose on boats. Hollow braided rope, on the other hand, can be spliced and often takes the form of inexpensive polypropylene and polyethylene rope. Double-braided rope is widely used and consists of a braided core covered by a braided cover. Depending on the materials used, it can exhibit elasticity that makes it suitable for anchor rode and dock lines, or it can be low-stretch and suitable for use on sailboats as halyards and sheets. Diameter for diameter, braided rope is stronger than laid rope. Other advantages include flexibility, ease of coiling, and resistance hockling or kinking. Splicing braided rope is more complex than splicing laid rope and requires specialized tools.
• Plaited rope is made by braiding double strands of line left-to-right and right-to-left. In plaited rope, the strands are not as small as they are in braided line. It is available as 8- or 12-plaited rope. Among the advantages of 12-plaited rope are that it’s comfortable to handle, doesn’t kink or hockle, is very flexible, and forms a “cubic” cross section, which is very good against the drums of windlasses or capstans. However, it stretches less than laid rope, though more than double braid. Splicing consists of weaving double strands of right-to-left into double strands of left-to-right and vice-versa.
• Nylon is very strong, but its most significant characteristic is its elasticity. This makes it very suitable for anchor rode and dock lines where, as I said earlier, its ability to stretch and recover acts as a shock absorber. Nylon absorbs water, which reduces its strength by 10 or 11 percent. Quality nylon rope treated with a lubricant that resists water absorption retains 95 percent of its dry strength when wet. When using nylon, estimate its safe working load at about 10 or 11 percent of breaking strength, and don’t use rode that is so strong it won’t stretch under the loads your boat can exert. Some things to consider: All rope can lose up to 50 percent of its breaking strength when knotted, because of the crushing effect of almost all knots; even good splices will reduce the strength of any rope by 5 to 10 percent.
• Polyester (Dacron) rope is suitable for halyards, sheets and other applications where elasticity is undesirable. It comes in laid and double-braid constructions. It does stretch about 2.5 percent when tensioned to 15 percent of its breaking strength. It shows good resistance to UV radiation.
• For serious racers — those with more sails in their inventories than they have underwear — high-tech materials such as Vectran, Technora and high-
modulus polyethylene (HMPE) fibers are available. All of these have virtually no stretch. Vectran works under very high loads relative to its breaking strength, so it’s good for static loads such as halyards for roller furling headsails. Vectran and Technora are moderately resistant to UV radiation. All rope, even wire rope, will stretch a little under load. However, there is another kind of stretch in some of the high-tech fibers. It’s known as creep, which is slow and permanent elongation under high loads over a long period. Vectran and Technora exhibit almost no tendency to creep. HMPE fibers, such as Spectra and Dyneema, have the highest strength-to-weight ratios. They’re tremendously strong but are slippery and don’t hold knots well. They have low melting points, about 300 F — lower than the temperature at which paper catches fire — and this can create problems at winches and multipart purchases. HMPE fibers do tend to creep.
3. Some caveats worth keeping in mind. Polyester double-braid rope is spliced by threading the core into the cover and the cover into the core, and then “milking” the cover over the splice to protect it. It looks neat and is very effective because the core and cover both contribute 50 percent to the strength of the line. However, I’ve seen the same technique improperly used to splice high-tech rope. When high-tech line is spliced, the high-tech core, not the cover, contributes virtually all of the strength. When completed, both double-braid polyester and high-tech splices look the same, but high-tech line requires a different technique. Question the person providing the splice as to how it will be made.
4. Have fun, be safe.
This article originally appeared in the May 2009 issue.