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How do I stop dock line chafe?

2017 September 1

Dear Boat Doctor,

I am having a problem with a dock line. The distance between the cleat and the chock is about 4 feet, long enough that the elasticity in the dock line “works” enough at the chock to wear through the line. How do I keep this from happening?

Jim Milada

Brown Deer, Wisconsin

Dear Jim,

Chafe is the enemy on a boat. Usually this is a problem with running rigging, but it can happen with dock lines too. The elasticity is what is getting you, the line moves back and forth in the chock, sawing on every stroke.

Typically an elastic line is best for dock and anchor lines because you want the rope to absorb the energy, you don’t want it to be transmitted to the boat. But in your case, you want minimum elasticity at the chock, while still allowing the rope to absorb energy. The answer is a hybrid dock line, a section of nylon spliced to a section of something very inelastic, typically Spectra/Dyneema.

You’ll want to splice a short section of Dyneema a size or two smaller than your dock lines with an eye on each end. The Dyneema can be smaller because it is so much stronger than nylon. The boat end needs to fit your cleat, the other end can be just a few inches long. The entire construction should be the length of your cleat to the chock plus 18 inches. You may need to adjust the length to accommodate the bury portion of the splice.

You’ll also need a length of nylon three-strand with a small eye on one end, and an appropriate termination on the dock end. 

Simply ring hitch the two together and you have a hybrid dock line, low elasticity where it goes through the chock and higher elasticity to the dock.