Mailport: June 2012
A Hot Topic
In regards to your July 2011 article on chafe protection: Readers should be aware that nylon lines can break no matter what there is for chafe protection. I’ve been a member of Boat/US’s catastrophe team for years and have worked a dozen hurricanes, so I’ve seen a lot of real-world line failure.
As nylon line has a fairly low heat distortion temperature (you can melt the ends with a match, right?), I’ve seen many failures where the line is welded into a solid doughnut around cleats or pilings. I’ve also seen the lines fail inside chafe protection. When you peel the three-strand line apart, you can see that the strands melted together where they touch. My take-away from this:
1. We are generally taught that nylon acts as a shock absorber in mooring and dock line applications. My experience has shown me that if the dock lines are stretching like a rubber band, they are creating energy, which equals heat. In a sustained storm, that heat will destroy the line.
2. Lighter dock lines will distort more. It’s my experience that most boats in storm situations have lines that are too small in diameter. Half-inch line is appropriate for dinghies; other than that, I would step up to a minimum of three-quarter inch.
3. Three-strand nylon appears to fail far more often than double braided.
4. Cheap import lines fail more often than high-quality line provided by domestic manufacturers.
When Hurricane Bob hit New England in 1991, I saw the Concordia Boats yard manager go out before the storm and slathered the mooring pendants of all the precious Concordia yawls with skid grease where the pennants passed through the chocks. It made an awful mess, but they didn’t lose a single boat even though 30 boats were lost in that same harbor.
We’ve discussed the heat issue before, most recently in the December 2007 report on our torture tests of used nylon three-strand, in conjunction with New England Ropes. And the debate over expensive double-braid versus more elastic three-strand is one we have wrestled with for years.
Our advice has generally been that it is most cost effective to go for a larger diameter high-quality three-strand and good chafe gear than an expensive, less-elastic, double-braid line, and most of the rope makers seem to agree. Elasticity (energy absorption) is a desirable trait in anchoring, mooring, and dock lines. However, heat is an issue, specifically, where a dock line or mooring pendant goes through a chock, creating a bend. When the fiber is both stretched and bent at the same time, the internal friction creates heat. Heat is less of an issue in a rain storm, unless the chafe protection keeps the rain out, and then you are making things worse by creating an oven. As we have pointed, some chafe gear (PS, July 2011)—plastic hose in particular—is often the culprit more often than the braid of rope because it contains the heat.
One trend is to regard the dock or mooring line as a two-component system. One component has stretch and another is low stretch. Here’s how Steven Parola of New England Ropes describes such a system:
“On a mooring pendant, you could have a section of nylon rope running from the mooring ball almost to the boat (for stretch), then attach a section of low stretch rope, such as STS-12, comprising high molecular weight polyethylene (HMPE) fibers, that runs thru the chalk and to the cleat. The ‘system’ approach is quite exciting, particularly if your boat/mooring is unattended over long periods of time; but the down side is that it is pricey, as compared to using a nylon rope and occasionally inspecting your line.”
With the 2012 hurricane season kicking off, we will be doing an update to our mooring/dock line and chafe gear reports in an upcoming issue.
Next: RNLI Correction