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What Types of Lines Should I Use on My Boat?

I am a die-hard boater and even in cold weather, you will often find me on my boat.  Often times when I walk down my dock, I find that I am the only one there.  While many boat owners leave their boat in the water during the winter months, a good percentage of them tie them up in the fall and do not return until warm weather comes back.  Because of this, I make it a point to walk the dock, checking lines and fenders on all of the boats to make sure there are no issues.  I know that some of my dock neighbors that come up in winter months do the same.  One of the things that I consistently notice is that many boats do not have the proper lines securing them to the dock. 

Let’s take a look at what types of lines should be used for various purposes on your boat. 

Dock Lines

Nylon is the best material for dock lines.  This is because it is strong and it also stretches.  Stretch is important because it allows the line to absorb the shock of the boat pulling on it in rough weather.  Three-strand nylon is the least expensive and works well.  It is also easy to splice if you want to do so yourself.  Braided nylon is a bit more expensive.  It is easier to coil and most people think it looks better.  It is also stronger but does not stretch quite as much.  Splicing of braided nylon is quite difficult and most people decide to preorder it in needed lengths rather than splicing it themselves.

One of the common mistakes that are made when many boat owners acquire dock lines is purchasing lines that are too small in diameter.  A 3/8 inch line is cheaper than a 5/8 inch line but if it snaps during a storm because it was too small to hold your 40 foot boat, saving $50 on a set of dock lines will suddenly seem trivial.  Spend a little more now for the right lines and you will sleep better at night.

The chart below shows you the proper size nylon line to use based on the size of your boat:

Boat Length
Nylon Line Size
Up to 27 feet
Up to 36 feet
Up to 45 feet
Up to 54 feet

If the cleats on your boat are large enough, consider purchasing lines one size above the required minimum size.  This is especially important if your boat is heavier than most or has more windage.  It is a small price to pay for a little more insurance.  Also, check your lines often.  If they are frayed or worn, replace them.

Three strand braided nylon rope is commonly used for dock lines and anchor lines.

Anchor Rope

Assuming that you are not using all chain, nylon is the best material for your anchor line (also known as rode) for the same reasons it is best used for dock lines, strength and its ability to stretch.  Having the right size anchor line is just as important as having the right size dock line. 

The rule is that your anchor line should have 1/8” of thickness per 9 foot of boat.  For example, if your boat is 27 feet in length, your minimum anchor line diameter should be at least 3/8” inch.  In either case, having at least 10 foot of chain between your anchor and the line is highly recommended to make anchoring more efficient and effective. 

Don’t forget that if you have a windlass, you must use a rope/chain size that fits it.  If you have the proper windlass for your boat, it will accept the proper size rode for your boat.  

For a bit more money, some boaters choose braided nylon for dock lines.

Towables and Throwables

Line for towables and throwables includes any line used for towing inflatable toys, attaching to life rings or towing other boats.  For these applications, you should use polypropylene rope.  The main reason for this is it floats.   It is much easier for a swimmer in the water to grab a line that is floating on top of the water and it is less likely that the line will not get hung up in your running gear because you can see where it is and it will not sink below the surface where your props and rudders are.  While nylon rope can be used for these applications, it does not float and may not be as effective or could render your vessel inoperable if it gets wrapped around your gear.  

A big benefit of polypropylene rope is that it floats

If you are considering towing a boat, know that polypropylene line is not a strong as nylon and you will need a much larger line to safely tow even a small boat (as much as ¾ inch diameter for a 22 foot boat).  If you do not have the proper equipment or you are not sure how to do it, you are better off leaving the job to the experts.

Do yourself a favor this off season and check all of you lines and make sure you have the rights ones for your boat.

Happy Boating

Captain Frank
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  1. Thanks for the reminder. Protection from the sun for coiled/stowed ropes is good also.

  2. I prefer good ones! Although I do have a bad one or two on my boat. One line that most fresh water boaters don’t have is a throw line with a monkeys fist.

  3. I live on the cost of Maine on a island, and very little protection from the nor’east . I have had very good luck with double braided And line savers. 3/4” bow 5/8 spring and stern . 22’ boat . It’s the surging that does the most damage. Especially when the seas are 16’ and higher ��

  4. 3strand nylon. After hurricane Ike boats US did a study and found it held up better than any of the other types line.

  5. I bought a spool of 3strand and spliced my own lines. If you have time, do that. Gave me confidence during Hurricane Florence. (It’s also much cheaper)

  6. Beware of "discount online" dock line from China. It will turn into powder in a year or less.

  7. The answer depends on the situation at hand. Braided line is good for temporary docking and only stretches 5%-6% under 15% load. Three strand twisted nylon line stretches 15% at 15% load and is what you should use for permeant (particularly with big tide changes) and storm application. For tropical storms, you want 3-strand nylon lines that are long enough to stretched with an extreme tide, and still retain the elasticity to keep your vessel centered when the tide recedes. A 9' tide generally requires a line longer than 17'...fairlead the line if necessary to obtain the length. The diameter of rope is determined by the size of your cleat. Unless you have a specific mooring plan, don't mix 3-strand nylon and braided line. Make your own eye splices and avoid knots, which substantially weaken the assembly.

  8. You should use ropes with some stretch in them, not the double braid!


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