Dock Line Death Test

25 Jan

In the book The Bad Girl, by Mario Vargas Llosa, a character named Arquimedes has a preternatural ability to tell where breakwaters and groins should be built. He can tell just by meditating on the sea whether the breakwater will serve its purpose or make matters worse. The best hydrologists and engineers in Lima always hired Arquimedes, because if they didn't their projects often ended up as expensive failures.

Pier 39 Marina, where I keep my boat in San Francisco, did not hire Arquimedes. It's hard to figure out the mechanics, because there are breakwaters and sea walls every which way, but the Pacific swell bores in there, and the surge is terrible. There are times when I look down one of the main fingers of the dock, about 150 yards long, and can see the whole thing rolling a good foot with the swells. One could ride the swell down the dock on a bicycle, but there are signs everywhere prohibiting bicycles.

Why do we put up with it? The location is great: right in the heart of the San Francisco waterfront, a straight shot to Alcatraz and Angel Island, and just three miles from the Golden Gate. But of course this is hard on boats and dock lines. I've had chocks and cleats ripped off my boat. In my first year there I went through over 300 feet of dock line. That's 3/4" dock line, which runs about a buck per foot, so $300.

Pier 39 Marina is the test bed for dock line systems, and I will pass on what I've learned in these few years:

1. Use chain where you can. Chain don't chafe…much. The surge at Pier 39 will even eat through 3/8" chain and cleats after a year or two, but it'll go through nylon line like butter.

2. Shock absorption is good. Yes, Nylon dock line stretches, but not enough. Yes, there are purpose-made marine shock absorbers on the market…we see lots of those in tatters around Pier 39. The only shock absorbers that last more than a season are tires. Pier 39 has an arrangement with a scooter shop and gets all the shop's used tires. They sell four for $15 and the $15 is a donation to the Bay Area Disabled Sailors. I just had some fire hose lying around, so I put it on the chain. The chain won't really damage the tire much. Likewise, the rope won't chafe much on the tire, but I put some hose there as a matter of habit.

3. Multiple lines are good. I can't explain this one either, but two lines last way more than twice as long as one line. In my experience, two lines last five to ten times longer than one. Maybe they shift each other around and find new places to wear. And of course if one breaks you've got a backup. Likewise, spring lines like the one below seem to help. My boat is limited because I have no midship cleats, but these spring lines seem to hold the boat in a web of tension, and lines seem to last longer.

4. There is no shame in tying broken lines together. At Pier 39 it would get too expensive otherwise, so most dock lines, like mine, seem to be a patchwork of chafed-through lines that tell a long story. Save the pretty, contiguous line for out on the water.

So I've got it almost figured out…almost. The rub, literally and figuratively, is where the line goes through the chock on the boat. Here I have gone through several rolls of reinforced hose, only too see the action at Pier 39 chew it full of holes, sometimes in as little as a week. And once the hose goes, the line isn't far behind.

There is a product called Chafe-Pro that will be put to the test, later this season.


  1. Clark Beek

    I’m guessing it’s expensive, but worth it. I’ve since moved far away from Pier 39, into a nice residential canal, where there is little surge. In fact, I’ve almost been considering getting rid of my patchwork dock lines and replacing them with something respectable.

  2. Dan K

    I highly recommend spectra tubular webbing for chafe protection… it is pretty amazing stuff. Recommend the zeppelin bend for connecting two lines… and generally don’t recommend any kind of waterproof reinforced hose for chafe protection because it stops water from getting to the line inside and water is the lubricant that helps prevent lines from chafing and melting–which is a very common mode of failure for docklines.

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