Dock Lines

[higgs]

This month's Practical Sailor had a test of old dock lines (10 - 12 years old) that found many of these lines had lost 75% of their strength. it also showed that on newer line, the elasticity of nylon was actually problematic as the stretching and contraction causes friction/heat and fibers can melt as a result. They also pointed out that the elasticity encourages a boat to sail while at anchor.How old are your dock lines?

 

[RichH]

I use 3-strand dacron for my docklines ...

Less UV damage, less 'stretch', stronger when 'wet', etc. but expensive and somewhat hard to find. Nylon is mostly a bad choice: subject to easy UV damage, subject to hydrolysis (analog to 'rusting'), etc. etc. etc. Most of the adverse characteristics can be remedied with added inhibiters to the base polymer but then it winds up more expensive than dacron. Dacron (polyester) is quite stable - your old polyester sweater should be in that landfill for at least a few hundreds of years.

 

[Ross]

My 5/8 nylon dock lines get retired when the loops

start to show excessive wear. 50% through one strand. Generally I change them after about 6 years. That way it only cost about a buck a month.

 

[Benny]

The lines just have to be a little stronger than

the pull the boat may place on them. I don't know if anyone has devised a formula to calculate the forces a boat may exert on its dock lines but as a practical matter they don't seem to be much. I can probaly pull using the strength in my arms and my body weight as leaverage about 200-250 lbs. I am able to hold or pull the boat over in my slip in winds of 35 knots by pulling amidship on a single spring line. In winds of 50 knots we are probably looking at 500 lbs but then divide the forces by two as you have a bow and a stern line and you are still looking at 250 lbs per line. With economy three strand docklines coming in breaking strengths of 3,000 to 6,000 lbs I dont think there is a problem here. More important than strength degradation would be its condition. If is chaffed and the strands are begining to unravel then it would be wise to replace. A 3000 lbs line that has lost 75% of its holding strength still will hold 750 lbs which should be more than adequate. I mostly change docklines when they chaff or get ugly. I never had one break on me. When a storm is forecasted I will double up on the lines but that's about it. Remember your dock line will hold just as much as the cleat attached to the dock. If anyone has a good formula I would like to see it as I have always been curious as to the forces involved.

 

[Roger (Ninette Manitoba)]

many lines; separate anchor points

My boat is only 1300# but I typically use 7 lines to secure it at its wet slip. It stays there all season, so I need to trust those lines from weekend to weekend. By the simply formula of 1300/7=185# to each line at the absolute maximum it they were suspending the boat, (which they are not), I trust my 7 lines. I use a bow spring, aft spring, bow, stern, amidship breast, and a line from the opposite stern quarter to the T dock when available. I change out lines when they show obvious signs of wear, rot, chafing through. In strom conditons, I double my lines. For each line there is a different anchor point on the anchor. Any single failure, would not result in a disaster. I also place ample fenders betweent the boat and dock, (3 on the dock , 2 on the boat) and an additonal fender on the opposite gunwale to protect against my neighbours boat, should either mine or his come loose.Watchful eyes and helpful hands at our club will often retie or secure boats that are endangering themselves and others, but primary responsibility is always placed on the owner to used adequate lines. We are fanatical about wraping halyards around the spreaders or bungeeing them to prevent halyard slap as well, but that is another story.

 

[higgs]

Benny

You make some very good points. I have never seen a dock line fail unless it was caused by chafe.

 

[Ross]

One day when the river was at flood

with the current running about 4 knots and my boat facing into the current I watched it drift back against the springs and stop . Then it woundrespond to the strech of the lines and head into the center of the slip and just hang in the current for several seconds before she slipped back for another cycle. It was completely gentle. We dock stern to the floating pier, with no finger piers so we are tied to cleats on the pier and the piles at the outer end of the slip. I keep the stern lines short and the bow lines as long as I can without banging into either pile at high tide. After about six years the bow lines start to show chafe wheere they wrap the piles so this year I servred them with number 60 seine twine. That seems to be helping with the chafe.