Dock Line Buying Guide: Size, Length and Material for Your Boat
Quick answer: Use nylon dock lines, because nylon stretches and absorbs shock. A common rule is 1/8 inch of diameter for every 9 feet of boat length: 3/8 inch for boats up to about 27 feet, 1/2 inch up to about 35 feet, 5/8 inch up to about 45 feet. Bow and stern lines should be at least two-thirds of your boat's length, and spring lines at least equal to your boat's length. Add chafe protection wherever the line rubs.
Dock lines are the only thing holding your boat in place when you are not on it. Lines that are too thin snap or stretch out in a blow, lines that are too short leave you no room to tie off properly, and the wrong material jerks your cleats every time a wake rolls through. Getting them right is cheap, and it protects your boat, your cleats and the dock. This guide covers size, length, material and how to set them up.
Step 1: Choose nylon
| Material | Stretch | Best for |
|---|---|---|
| Nylon double braid | Moderate | Most dock lines. Strong, soft to handle, absorbs shock |
| Nylon three-strand | High | Budget lines and mooring, easy to splice, stretches more |
| Polyester | Low | Sail lines and halyards, not ideal for docking |
| Polypropylene | Low, floats | Tow lines and throw ropes, weak in UV, not for docking |
Nylon's stretch is the point. It acts like a shock absorber, so wakes and gusts do not yank the cleat.
Step 2: Size the diameter
| Boat length | Line diameter |
|---|---|
| Up to about 27 ft | 3/8 in |
| About 28 to 35 ft | 1/2 in |
| About 36 to 45 ft | 5/8 in |
| About 46 to 55 ft | 3/4 in |
Go up a size for heavy boats, exposed slips or hurricane prep. Check that your cleats are big enough for the line you choose, with roughly 1 inch of cleat length for every 1/16 inch of line diameter as a common guide.
Step 3: Choose the length
- Bow and stern lines: at least two-thirds of the boat's length.
- Spring lines: at least the boat's full length. They run diagonally and need room.
- Extra lines: carry at least one longer line for rafting, fuel docks and unfamiliar slips.
Too long is easy to coil and stow. Too short leaves you stuck.
Step 4: Know the basic setup
- Bow line: from the bow cleat forward to the dock.
- Stern line: from the stern cleat aft to the dock.
- Forward spring: from the bow aft to the dock, stops the boat moving forward.
- Aft spring: from the stern forward to the dock, stops the boat moving backward.
Leave enough slack for the tide range at your dock, and use properly sized fenders between the boat and dock.
Step 5: Prevent chafe and shock
- Chafe guards protect lines where they cross the gunwale, chocks or pilings. Chafe is one of the most common reasons lines fail in storms.
- Snubbers add extra shock absorption for exposed slips and surge.
- Inspect regularly. Replace lines that are hard, faded, fuzzy or flattened.
Step 6: Tie off correctly
- Use a cleat hitch on cleats: a full wrap around the base, a figure eight over the horns, and a locking turn. It holds well and releases easily.
- Use a loop on pilings. A spliced eye or bowline dropped over a piling lets you adjust the line from the boat.
- Keep lines clear of sharp edges and use chocks or fairleads where the boat has them.
- Coil or flake the excess so no one trips on it and it does not end up in the water.
Common mistakes to avoid
- Tying too tight. Lines with no slack can snap cleats or hang the boat as the tide drops.
- Using old, stiff lines. Nylon loses stretch and strength as it ages in the sun.
- Skipping spring lines. Bow and stern lines alone let the boat surge forward and back into the dock.
Quick checklist
- Four lines minimum: bow, stern and two springs
- One extra long line for rafting and unfamiliar docks
- Nylon, sized to your boat length
- Chafe guards for every line that touches an edge
- Snubbers if your slip sees heavy wake or surge
Our picks
All in stock at Boat Supplies Direct. Dock line sizes sell quickly, so check the full collection for your size.
Double braid nylon dock lines
Sea-Dog Double Braided Nylon, 1/2 in x 25 ft for boats around 28 to 35 feet, or 5/8 in x 35 ft for larger boats. For spring lines on bigger boats, 5/8 in x 50 ft.
Snubbers and shock absorbers
Attwood Mooring Snubber Kit with 3/8 in x 20 ft Line or the Snubber TWIST.
Chafe protection
Sea-Dog Leather Mooring Line Chafe Kit, 1/2 in, also in 5/8 in.
Easier docking
Panther Happy Hooker Mooring Aid for hooking pilings and cleats from the boat.
Frequently Asked Questions
What size dock line do I need for my boat?
A common rule is 1/8 inch of diameter for every 9 feet of boat length: 3/8 inch up to about 27 feet, 1/2 inch to about 35 feet, and 5/8 inch to about 45 feet. Size up for heavy boats or exposed slips.
How long should dock lines be?
Bow and stern lines should be at least two-thirds of your boat's length, and spring lines at least the full length of the boat.
Is nylon or polyester better for dock lines?
Nylon. It stretches to absorb shock from wakes and wind. Polyester stretches very little and is better suited to sailing lines.
What is the difference between double braid and three-strand dock line?
Double braid is softer, stronger and stretches less. Three-strand is less expensive, stretches more and is easy to splice.
How many dock lines does a boat need?
At least four: bow, stern and two spring lines, plus a spare long line for rafting and unfamiliar docks.
When should I replace dock lines?
When they become stiff, faded, fuzzy, flattened or worn at chafe points. Inspect them regularly, especially before storm season.
This guide is general information. Size up lines and add chafe protection for storms, and follow your marina's requirements.
