Do Your Dock Lines Need Replacing?

Dock Lines

I walked around the marina a few days ago and looked at the dock lines that were being used to secure the boats in their respective slips.  I was pretty amazed at what I saw.  Some boats were secured properly.  Other boats were not secured well at all.  Some of the poorly secured boats showed significant chafe and wear on the lines (a couple boats actually had lines that had broken and the owner simply tied the two broken ends in a knot and retied the line to the cleat on the boat).  Some of the boat owners were using line that was significantly undersize for the boat - - one eighth inch line for a 26 foot long boat for instance.  Many boats were tied to the dock with dacron (doesn’t stretch much) line.  Every time one of these boats surges against the line, a considerable shock is imparted through the cleat to the cleat’s fasteners and to the deck of the boat.  How many times can you bend a credit card before it breaks????  Remember that we have experienced some very strong wind storms recently.  A dock line with only what looks like a little bit of chafe will be considerably weakened.

So, here is some information compiled by West Marine in their catalog and on-line in the West Advisor –

Dock Lines:

What they do – Dock lines secure your boat to a dock, or to another boat when rafting, either temporarily or semi-permanently.  These applications demand different types of dock lines.

How they work – When your boat is away from its regular slip or mooring, you need to have some designated nylon lines aboard, preferably with spliced eyes, ready for use when you tie up somewhere.  We call these transient dock lines.  The eye in the end is easily passed around a cleat or piling by someone on the dock and the bitter end is adjusted on board.  There are dozens of combinations of diameters and lengths.

Permanent dock lines are also made of nylon, but differ from transient dock lines in several ways.  First, they must be protected from chafe, the enemy of all lines in constant use.  This calls for leather, rubber or fabric chafe gear where the line passes through the chocks, and possibly a chafe sleeve on the eye where it goes around the cleat on deck.  At the dock, lines should be protected from chafe using eye splices and shackles if the dock has rings, or eye splices and short lengths of chain if the dock has cleats.  Permanent dock lines should be cut to fit the particular boat in the slip.

What to look for – Dock lines should be made from nylon, which has a superior combination of strength and stretch.  Both three-strand and braided construction are common.  Three-strand stretches more, is very abrasion and snag resistant and less expensive.  Braided nylon is stronger, comes in colors, and has a nice feel or “hand”.

Diameter – We recommend one eighth inch of line diameter for every nine feet of boat length.  Larger lines will wear longer but stretch less.

Boat length and dock line diameter:

Up to 27 feet - - three eighth inch diameter

28 to 31 feet - - seven sixteenth inch diameter

32 to 36 feet – one half inch diameter

37 to 45 feet – five eighths inch diameter

46 to 54 feet – three fourths inch diameter

Length of line – Transient dock lines should be about two thirds of the boat’s length when use on the bow and stern.  Spring lines should be equal to your boat’s length.

Here’s an of example of good anti-chafe gear.

Here’s some examples of dangerous dock lines in use.

 Lines chafing...

This dock line has actually chafed through one of the three strands...

This line is way too small (diameter) for the boat

And more chafe...

 

Your boat is one of your most expensive investments.  Having the wrong dock lines or worn out dock lines will jeopardize that investment.  Next time you are out to your boat, take a close look at the dock lines and make  corrections (if needed). - This does not mean find an old jib sheet to tie the dock to the boat with. -  If one of your lines breaks during a storm, your boat will start banging against the dock, piling, or other boats.  And, you will find out just how good your boat insurance really is.