Great question. I will use some 40 years of experience in the pleasure and commercial boating field to answer that question. The answer is , I don’t have the foggiest idea. But I will say if you take care for your dock lines as much as you take care of your boat, they will last a long time.

I had a client many years ago that purchased a complete set of new dock line. The vessel was a 165 ft converted ocean tug. The lines were 1-1/2” / 36mm nylon double braid and there were 8 lines of various lengths. Ten year later I received a request from the same captain, the same vessel for a new set of lines. I commented it had been ten years since he had ordered the previous set. His response was, if you take good care of them and pay attention and make sure your crew is paying attention, they will last a long time.

Just recently I delivered a set of lines to a client, similar size vessel, and about 6 weeks after receiving the lines, four of the six lines were severely damaged to the point the lines were no longer useful. One night of severe weather can destroy a set of lines.

A little common sea sense and paying attention to conditions and taking some corrective action; you can save your lines. Maybe not 100 % but certainly a solid 75%. And however many lines you require to tie up, add another 2 lines to your inventory; either as backup for a damaged line or to double up on one or two of the lines that are under a heavy load. When buying dock lines, make certain they are of the correct tensile strength for the job.