Choosing the Right Dock Lines

That is to say - It is rope until it has an eye or is on the boat.  Thereafter it is a line.

We sell custom dock lines.  The construction, diameter, length, eye size and color can be chosen by our customers. In our capacity as advisors we provide information to numerous boaters on a daily basis concerning our dock lines. The information that follows contains much of what we discuss.

 The first line of each paragraph summarizes the section.  Please read the full numbered section for more details.


There are a number of important factors in choosing the right dock lines.  Here are just a few and why they are important.


1. Material - Nylon is best

Nylon is generally considered the best material for dock lines. Important aspects are its strength, stretch and durability over time. Polyester and Polypropylene are sometimes used but less extensively than Nylon.


2. Construction: Three Strand has a history. Double Braid has the most advantages

Two types of nylon construction are commonly used.  One is three strand twisted often referred to as  three strand or 3 strand and the other is double braid often referred to as braided or yacht braid. 

This picture shows three strand. You will notice that the strands are elongated rather than braided at angles. This picture shows the construction of double braid. 

Both double braid and three strand nylon make excellent dock lines.  Three strand is less expensive than double braid and enjoys a long established presence in the boating community. Double braid with its finished appearance, easy handling and variety of colors makes it the choice of most boaters. Please click to see colors.


3. Appearance and Handling:  Double braid handles better and looks better. Use whipping color to show length.

Double braid has a softer feel and therefore provides easier handling.  Because of its weave it is more flexible which makes storage easier. We offer 18 colors in double braid and 2 colors in three strand. Many boaters feel strongly about the proper color whether to complement the colors of their boat or use color to indicate different line lengths. 

Double braid has a finished, professional appearance.  The end of the rope is embedded neatly when splicing the eye and whipping is added to the throat of the eye and the bitter end.  Different colors of whipping can be used to designate line length. Please click to see an example of black whipping.


4. Breaking Strength: Double Braid is stronger

Both three strand and double braid have excellent strength.  Here is a breaking strength comparison for three commonly used diameters.

Rope Construction




Three Strand




Double Braid




Breaking strength numbers are important since they show the maximum load that can be handled by each construction.  For a given diameter, the higher breaking strength of double braid allows it to withstand a broader range of conditions than three strand.  The general rule is to restrict the load on the line to less than 25% of its breaking strength.  Consistently exceeding this number will shorten the life of the lines. It is extremely difficult for a boater to know  the load their boat places on their lines. Using the diameter chart that follows along with a “gut feeling” can go a long way toward making the right diameter decision. Load calculations will be the topic of another article.  


5. Line Diameter:  Use ½” if your boat is 25’. Use ¾” if your boat is 50’. Use 5/8” for a size in the middle

Our web site shows suggestions for matching line size to boat length.  As you can imagine this is a rough estimate since the combination of boat designs and boating conditions are virtually unlimited.  Here are the diameter guidelines we use:

Boat Length

Inland Waters

Coastal Waters

25’- 35’



30’- 45’



40’- 55’



50’- 65’



60’- 75’



Inland and Coastal Waters: We believe it is important to allow for extreme weather conditions.  Often coastal waters are less protected from wind and boat wake. This suggests that slightly larger lines be used in coastal areas to predictably stay within the 25% load limit.

Line Loading: As previously mentioned, lines should be sized to limit the load to about 25% of the breaking strength.  Not knowing when or if conditions will occur that could overload the lines some boaters choose to go with slightly larger lines to be on the safe side.  In this regard, we have incorporated some conservatism into our guidelines.

Traveling Lines vs. Home Port Lines: It is easier to anticipate stress conditions at a home than while traveling.  Unexpected wind, current, and docking conditions are frequently encountered while traveling. For this reason we recommend slightly larger lines to handle unknown conditions while traveling.

Boat Cleat Size: We are referring to cleats on the boat rather than cleats on the dock. While this consideration would seem to be of low importance, it is vital in many situations.  Some cleats are too small for a given line diameter. 

A common design of cleats is a “hollow based” cleat.  This picture shows the hollow base and the horns of the cleat.  Frequently the eye of the line is pushed through the hollow part of the cleat and then wrapped around each horn. An issue is the space through the hollow base and the height of the horns above the mounting surface.  If the line is too large it will not fit the cleat and cannot be used regardless of its suitability otherwise.


6. Line Length: Make bow and stern lines 2/3 length of boat, make spring lines ¾ length of boat and make breast lines ½ length of boat

Here are our suggestions for line lengths:

Bow and Stern Lines

     2/3 of boat length

Breast Lines

     1/2 of boat length

Spring Lines

    3/4 of boat length unless fixed dock then full boat length

Types of Lines:  Commonly used lines are bow lines, stern lines and spring lines. As the names imply bow and stern lines are used for tying the bow and the stern to the dock or piling.  Bow lines and stern lines are usually shorter than spring lines since spring lines are used to restrict forward and backward movement of the boat and do this job most efficiently when they are attached some distance (small angle) from the boat cleats to the dock cleats or pilings.  This picture shows an example of using bow lines, stern lines and spring lines.

Home Port Lines and Traveling Lines:  The length of home port lines can be determined fairly easily since both the position of the boat cleats and the dock cleats are known.  For traveling lines determining length is more difficult and usually involves making them longer to cover a variety of docking situations.

Bow Lines:  Bow line length depends on the distance between the bow cleat and the dock cleat.  Boats with a high free board (height from the bow cleat to the water) will require a longer line to reach the dock cleat.  As mentioned previously the length of home port lines can be accurately determined based on measurable distance between bow cleat and dock cleat.  Traveling lines are another matter.  One suggested approach to determine the length of traveling bow lines is to use a long dock line attached to the bow cleat and place the opposite end at an exaggerated location on the dock to simulate an extreme cleat placement.   

Stern Lines:  Stern lines are similar in function to bow lines in that they are used to hold the stern close to the dock.  A frequent method of tying stern lines is to attach the line to the stern cleat that is away from the dock.  A “cross tie” such as this does a better job of holding the stern to the dock than a tie to the stern cleat closest to the dock “close tie” because the height of the stern above the dock in a “close tie” allows the boat to act as a pendulum and move away from the dock the distance of the pendulum.  The “cross tie” does not have as much pendulum effect and therefore keeps the distance from the dock relatively constant. 

Spring Lines:  Spring lines are used to restrict forward and backward movement of the boat.  Consequently one spring line is usually tied from a boat cleat close to the bow to a dock cleat closer to the stern. The companion spring line is tied from a boat cleat closer to the stern to a dock cleat closer to the bow. 

Breast Lines:  Boats that have a breast cleat (approximately mid-way between the bow and stern) frequently tie both spring lines to this cleat and extend them fore and aft for attachment to dock cleats. 

Floating or Fixed Docks: Floating docks are designed to float up and down as water levels change.  As a result required line lengths stay the same regardless of water level. A boat tied to a fixed dock will float higher and lower relative to the position of the dock as the tide changes.  With a fixed dock particular care needs to be given to the method of line tying and consequently the length of lines needed. 

With a fixed dock the entire boat becomes a pendulum as the water rises and falls.  Longer lines are usually needed for bow, stern and spring lines to achieve the desired position of the boat relative to the dock.This allows the boat to act as a pendulum without placing undue stress on the cleats and the lines. Any boater who has gone to sleep at high tide looking at the boat in the slip next to them and then awakened during the night to see only the part of the dock that was previously underwater, can appreciate the need to carefully position dock lines in high tidal change areas.

Docks with Pilings: Pilings are often seen with short dock walkways.  It is not uncommon to see a walk way that is considerably shorter than the length of the boat with pilings at the bow and stern on both starboard and port sides.  Tying to the pilings allows the boat to remain in position in much the same way as tying to a dock.  The same or even more care needs to be taken in high tidal change areas.  This is another example of the need to add length to traveling lines. Please click to see a common attachment to pilings.


7. Number of Lines Needed:  Four are necessary but six feels awfully good

Whether docking at a long fixed dock or at a short fixed dock. The use of pilings, cleats and bollards along with dock lines to control the effects of wind, current and tidal change often involve tying lines, checking the movement and then possibly retying until you get the desired effect.  Sometimes four lines are just not enough.  We recommend six lines (maybe more) unless you really know your docking situation. Please click to see a docking example using more than four lines.


8. Eye Size: In most cases the minimum is 18”.  24” is recommended for 5/8” and larger

Measurement:  Our method of measuring eye size is frequently used throughout the industry.  Pretend you hook your finger in the eye and pull it straight.  Two lines forming the eye are then side by side.  Measure the length of the two lines side by side and this is the “eye size”.  For example, if a line has a 24” length (size) and the eye is opened to form a circle, the inside diameter of the circle is approximately 15 inches.  Please click for an illustration of eye size.

Commonly Found: Many boaters have experience with dock lines purchased at retail stores that usually have 12” eyes.  In this case the inside diameter of the eye would be about 7-1/2”.  This small eye is often stretched in an attempt to make it fit over larger cleats.  It sometimes has to be “wrestled” to remove it from the cleat after it has been in place and has formed itself around the cleat. Many boaters have come to assume that this size is standard in the industry.

Larger Preferred:  While we will make any size eye that is requested by our customers, as a standard, we prefer larger eyes. Larger eyes provide the advantage of easier attachment to larger cleats, pilings and bollards as frequently encountered on lock walls. We have found no significant disadvantages.  An example of a larger eye size would be a 24” eye that we consider standard on our lines that are ¾” or larger.  The inside diameter of this eye would be about 15” when opened to form a circle.

Making the Transition:  Many boaters who have used only 12” eyes and visualize an eye twice this size hesitant to move to an eye this large.  Usually the concern is the eye slipping off the cleat because the eye is larger than the horns of the cleat.  This typically doesn’t happen because the common method of tying to a cleat with a hollow base (click to see example) consists of sliding the eye through the base and around the horns.  Even the largest eye would not come loose with this tie.  In rare cases when the eye is only laid over the cleat there is a modest tension on the line in controlling the boat that serves to hold the eye around the cleat.

The Results: We often hear our customers express their pleasure with the larger eyes.  I have no memory of someone being disappointed and wanting to move to a smaller eye. 

Standards: As previously mentioned, we will make any eye size our customers request but here is what we consider standard eye sizes for three typical line diameters.


1/2” Diameter Line

5/8” diameter line

3/4” and larger diameter line

Length of Eye when pulled straight




Diameter of Eye when open to a circle





Sometimes 12” on request

Sometimes 18” on request

Virtually no request for smaller eyes.


9. Eye Construction:  Eyes are formed by splicing the end of the line back into the body. This results in a very strong connection.  The throat at the base of the eye is whipped with wax whipping thread as is the bitter end. Colors of whipping can be used to designate line length.

Splice is a Good Thing:  The rope that is used to make dock lines has an incredible breaking strength.  When an eye is made by tying a knot it loses almost 50% of its strength due to the knot.  A splice retains over 95% of the breaking strength . In addition to strength, splices are neat, give a finished look, and make lines easier to handle. Please click to see an example of splicing. 

Whipping Finishes:  You will also notice the winding around the base of the splice and the opposite end of the line.  This is whipping using waxed thread.  Whipping serves to add strength, prevent frazzling, provide a professional appearance and allow designation of line lengths by using different colors of whipping thread. Please click to see color palette of whipping thread.


This is all for now.  Please stay tuned for updates and related articles. This article was written by Wayne Prichard.

Copyright 2013