T&T: Dock line elasticity

[LRZeitlin@aol.com]

In a message dated 4/1/07 12:00:53 AM, Sven writes:


> Quoting Brian Toss, in The Riggers Apprentice, Page 22: "Because it 
> is intrinsically more elastic, three-strand is the best choice for 
> mooring and dock lines" ... " As near as I can tell, the only reason 
> that people use braided rope for these applications is that it looks 
> more modern."
>
> Since The Rigger's Apprentice is pretty much the bible of rope, 
> splicing and rigging I would follow his advice.
>
>

This is a case where a nugget of wisdom is expanded into a boulder. It is
true that three strand twisted nylon line is more elastic than braided nylon
line. Twisted line may be expected to stretch up to 15% when loaded to 50% of
its
breaking strength while braided line will only stretch 5% under the same
conditions. But with regard to short dock lines the stretch factor is almost
irrelevant. Dock lines fail primarily because of abrasion. To provide a margin
of
security, dock lines are usually far thicker than required for the tensile
loading. A 5/8" line will probably rip the cleats out of an average sized boat
or
dock before it stretches to an appreciable extent.

Braided line generally has more resistance to abrasion than twisted line and
does not kink as easily. It makes a good dock line even though it is slightly
more expensive than twisted line. In my opinion, the best dock line is solid
braided nylon. It is a bit tricky to make the eyes but once you master that
skill you have a low cost wear resistant line that will not kink even if
thrown
in a heap on the deck.

In my case, I simply use dock lines cut out of the mid section of an old
anchor rode. The trick I have never quite mastered is keeping them out of the
propeller when reversing away from a dock.

Larry Z


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