Selecting the dock lines for my Greenline 33
August 8, 2017
Few weeks ago a friend of mine offered help and mentioned that “he will go to supply store and buy a set of docking lines for me”. I had to reject the offer. I spent several evenings researching dock line types and brands and there was no way to know which brands/colors will be available in the store. Why my friend found it amusing spending time researching best dock line brands, this is just the way I buy stuff. I like it. And I am pretty good at it.
Below is the summary of my research. Things about dock lines you never wanted to know but have been forced to find out…
Material
All dock lines should be made from nylon. It is strong, stretchy and resistant to sunlight. If you want to know more - read http://www.boatus.com/boattech/casey/docklines-casey.asp
Rope type
The main types of rope construction for dock lines are “3 strand”, “double braid” and “mega braid”. I picked double braid because it is stronger, softer and coils well in any direction (benefits of 3-strand: it is more stretchy and cheaper). Also double braid comes in many colors, so you can match the lines to the trim or canvas. “Mega braid” is used on large boats and was not on my research list.
Thickness and length
There are several guides online on selecting the right thickness and length. They all (more or less) agree with each other. If you are going to a larger than recommended size - make sure that your cleats will take it.
Note: Navigating Chittenden locks (aka Seattle Ballard locks) requires 2 x 50ft dock lines with 12″ eye. If you have a sub-40ft boat your standard spring lines are probably not long enough, so make sure to buy extra. You will use these long lines in the large lock when you tie to the wall. And you will not know in advance which lock you go through (small or large) and how will you tie (to the wall or raft to the other boat). So just always carry 2x50ft onboard.
Brands, strength and price
Here is the interesting part. Minimum breaking strength varies by almost 2x between the “basic” nylon ropes and high-end brands.
| Make | Minimum Breaking Strength for 1/2 inch rope | Price per foot for 1/2 inch |
|---|---|---|
| Generic/noname | 5400 LBS (from the engineering textbook) | $0.60 |
| Seadog | 4400 LBS | $1.00 |
| New England Ropes | 7600 LBS | $1.40 |
| Westmarine (New England) | 7600 LBS | $1.30 (full price) |
| Samson | 7900 LBS | $1.30 |
Westmarine-branded dock lines are made from New England Ropes nylon. Every couple months https://westmarine.com has a sale on their dock lines (20% off) and this is the best deal on pre-sliced high-quality dock lines. Between the sales the best deal is Samson-branded lines from https://www.fisheriessupply.com
Buying rope in bulk (in 600ft spools) is ~40% cheaper, but then you are stuck with the single color and have to splice yourself. If instead of splicing you tie a knot - that reduces rope strength by at least 30% (while eye-splice keeps full strength).
All “top brand” lines are very soft. Upon close inspection you can see “top brand” braided part is made from twisted threads. Where all “basic” lines are braided from un-twisted threads. This is a reliable indicator of the “quality brand”. I could not find out how this twisting affects the functionality, but I believe that it helps with internal abrasion. See this paper for details - Abrasion and Fibre Fatigue in High Performance Synthetic Ropes.
Here are the pictures of the few lines I had around the house.
New England Ropes - very soft, notice how well it coils under own weight. SeaDog has a slightly better construction quality than “generic”, but is stiffer.
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