Boating Safety - Fenders and Docklines

June 13, 2013   Notice:  NOT Bumpers or Ropes !  Bumpers are for dinghies and strollers and a dockline (or any line on a boat) stopped being a "rope" the minute you walked out of the store. mermaid fenderSeriously, walking the docks you can see a vast array of fenders and various docklines ranging from mermaid fenders, "hole on each end" spherical and "line through the middle" fenders along with docklines which range from 1/4" clothes line (REALLY !) to 3/4" color coordinated braided lines with spliced eyes. So,  what should you really be using to protect your boat ? So let’s start with fenders.  Based on manufacturer’s specifications and experience, the following chart shows the approximate (suggested) size.  Remember, you can always go bigger !  

Boat Size

Hole in each end or

Line through the middle fenders



20-30 ft.

6.5” X 16” to 8.5” X 20.5”

9” to 12”

30-40 ft.

10.5” X 27”  to 13.5” X 35”

12” to 15”

40-50 ft

13.5” X 35” to 18” X 50”

18” to 24”

50-60 ft.

18” X 50” and larger !  or Custom inflatable fenders

24” or larger

  As a rule, a minimum of three fenders are required for a boat alongside a dock.  One at the beam max point, one forward and one aft near the transom.  Placement varies by boat design, but more, rather than less is the rule. Each fender should have an adequately sized line of generous length to fasten it to the boat. Figure at least ¼” X 3’ for small fenders, 3/8” X 6’ for medium and ½” X 8’ for larger fenders, again sized for your boat and freeboard (height above water). The lines can be either 3 strand nylon or braided, NEVER polypropylene (breaks down with UV exposure) or hardware store clothes line which has no strength or salt water resistance. They should be tied to the boat using two half hitches  (See how HERE  ) from the solid base of the lifeline stanchion or vertical railing support  (never from the lifeline or upper rail)  See diagram:  Fenders Hanging    They must be set vertically to protect the boat, so lower them first to just touch the water and then pull them up two inches or so.   Also when you leave the dock all fenders COME IN. Swing them up onto the boat still tied on or untie and stow them. Remember, leaving them down underway is sloppy seamanship and indicates to others you are a neophyte with no boating experience !  They (and I) will go to lengths to avoid you. Can you use clips or hooks or one of the myriad fender hanging “thingies” available ?   Well, yes, BUT you have far less adjustment and placement options with them.   If you always do exactly the same thing with your boat and never go to different docks or raft up, OK.  Otherwise, have your crew practice the two half hitch knot. It’s also the knot you should use to tie things to the roof of your car, on trailers or anywhere you have to cinch tight and tie off. While you are practicing you knots, work on perfecting the Cleat Hitch….  Click Here  fender_diagram2         fender_diagram - Rafting   Docklines Docklines, like fenders, should be appropriately sizes for your boat and made from an elastic material, usually nylon. Some braided lines are made from polyester, but polyester has less stretch than nylon. Avoid any aramid fibers or high strength- low stretch fibers with technical sounding names. Those lines are for racing sailboats, not docklines, no matter how colorful they are.  Plain old nylon resists UV exposure, has the right amount of stretch vs. tensile (breaking) strength, is fairly abrasion resistant and costs less.  The stretch is necessary to absorb the shock loads that come when a boat surges or is hit with a blast of wind.  Also avoid polypropylene, (like ski tow line) which has very low UV resistance, gets brittle and has low breaking strength and stretch characteristics.  Nylon is the way to go.   Suggested Dockline Sizing

Boat Size

3 strand Nylon or Braid

up to 25'


up to 35'


up to 45'


up to 55'


up to 65'


  Note: for In-the-water winter storage or storm lines, go the next larger size or double up for strength and chafe resistance.   Always use chafe gear for sharp bends, long term or abrasive point protection.   Plan on at least one bow line, two spring lines and at least one stern line.  Remember the spring lines keep your boat from moving fore and aft and the bow and stern lines from moving in and out.  Usually the eye on the line goes on the cleat on the boat and the dockline is tied to the cleat on the dock. Ask the experts at the Norwalk Cove Ships Store or at the Rex Marine Center for help choosing the correct equipment.   By Captain Rick Delfosse  203-216-7800 Rick is a Coast Guard captain, US Sailing-certified instructor, Connecticut and New York certified safe boating instructor and a National Safe Boating Council close-quarters boat-handling and open water boat handling instructor.   He also conducts coastal cruising and boating skills seminars. The owner of a 43-foot pilothouse cutter and an Aquasport powerboat, he has extensive cruising and one-design, coastal and offshore racing experience.  

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