Captain John's Sailing Tips Newsletter
Don Launer's Guide to Sailboat Docking Lines
Donald Launer has held a US Coast Guard captain's license for over 35 years and has written more than 300 magazine articles and 6 books on boating, including "Navigation Through the Ages", and "The Galley: How Things Work Plus Upgrading Ideas". For 15 years Captain Launer was Field Editor for the yearly Waterway Guide, and he is currently the Contributing Editor for Good Old Boat Magazine. He has won two Emmy Awards for his work as Technical Director of TV coverage at the Olympics.
The majority of sailboats spend more time at the dock than actively sailing. This makes the selection of dock-lines especially important. Nylon dock lines are the material of choice. The nylon dock line can be either 3-strand laid, or braided.
The advantage of braid is that it comes in attractive colors that can match your sail-covers; it rarely kinks; it is easier to coil, and it's easy on the hands.
The downside is that it tends to chafe more easily than 3-strand laid line; it is more expensive, and becomes a daunting task if the do-it-yourselfer wants to create an eye-splice (which has a higher breaking strength than a knot). For this reason most chandleries sell braided dock lines with eye-splices that have been done by professionals.
But why not use polyester (Dacron, in the US or Terylene in Great Britain) lines? The reason is that nylon lines stretch. The rule-of-thumb is that a good quality nylon line will stretch 25% of its length at 50% of its breaking strength.
This stretch provides the advantage of creating a shock-absorbing effect. This shock absorption helps prevent a dock-line from breaking, or from putting severe and sudden strains on dock or deck cleats. Although double-braided nylon line is 15% stronger than 3-strand, it stretches less, providing less shock-absorption.
Of course, when a big blow is moving your way, large diameter lines should be installed in place of, or in addition to, your normal lines. But remember, larger diameter equals less stretch. Double the diameter and you cut the stretch to one-quarter (the stretch is inversely proportional to the square of the diameter). The advantage is that larger diameter lines are less likely to fail from chafing.
An unexpected finding by MIT after hurricane Gloria, showed that many nylon lines, which were angled across a chock, failed internally when they melted from the friction created by the repeated stretch-cycles. Most high-quality nylon lines are treated with a lubricant to reduce this type of failure- but this lubricant dissipates with the aging of the line.
Although chafing gear is a good idea whenever a dock line goes through a chock, the possibility of melting the nylon through the constant stretching cycles can be acerbated when some types of chafing gear are used, since they can trap the heat being created and prevent the cooling rain or spray from reaching this critical point. Instead, abrasion-resistant, woven polyester sleeves can be used which allow the heat to dissipate as well as letting water in to cool the line. These sleeves are available from most marine chandleries.
Another little-known quality of nylon line is that when wet it loses about 15% of its strength (which returns when the line has dried out). Since we are most concerned with strength during storm conditions - when the line is wet - this is another item to factor into the equation of storm-line size. It's also important to know that colored line has just slightly less strength than natural.
This brings us to the question of nylon line quality. There is a wide range of differences in nylon lines, with the cheaper nylon stretching more and having considerably less abrasion-resistance and internal lubrication - so don't skimp here.
It's much cheaper buying high-quality line than buying a new boat. Insurance companies estimate that up to half of the boat damage due to hurricane Andrew, that hit Florida in August 1992, could have been prevented with adequate dock lines.
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Download these FREE Cruising and Sailing Navigation Guides!
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//www.skippertips.com/members/1787.cfm
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//www.skippertips.com/members/1783.cfm
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//www.skippertips.com/members/1779.cfm
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//www.skippertips.com/members/1773.cfm
Dock a Boat Like a Pro - Use this Secret for Picture-Perfect Docking Control!
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//www.skippertips.com/members/1766.cfm
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