Boat Fender Buying Guide: What Size and How Many Fenders You Need
Quick answer: Plan on about 1 inch of fender diameter for every 4 to 5 feet of boat length, and carry at least 3 fenders per side (one more for every 10 feet over 30). Size up for heavy boats, exposed docks and rafting up. Add fender covers to keep fenders from scuffing your gelcoat, and use proper fender lines so they hang at the right height.
Fenders are cheap insurance. A single scraped hull or cracked gelcoat repair costs more than a full set of quality fenders. Yet undersized fenders are the most common mistake at the dock: they roll out of place, compress flat in a surge and let the hull touch. This guide covers sizing, how many you need, fender types, and how to hang them.
Step 1: Size by boat length and weight
Here is a typical sizing chart for cylindrical twin-eye fenders. Go one size larger for heavy displacement boats, high windage, or docks exposed to wake and wind.
| Boat length | Fender diameter | Example sizes |
|---|---|---|
| Under 15 ft | 3.5 to 4.5 in | Polyform G-1, G-2 |
| 15 to 25 ft | 5.5 to 6.5 in | G-3, G-4, HTM-1 |
| 25 to 35 ft | 8 to 9 in | G-5, HTM-2 |
| 35 to 45 ft | 10 to 11 in | G-6, HTM-3 |
| 45 ft and up | 12 in or larger | HTM-4, round A-series |
Fender length matters too. Longer fenders cover more hull and stay in place better as the boat moves.
Step 2: How many fenders?
A good baseline is three per side for boats up to 30 feet, adding one for every additional 10 feet. If you raft up with other boats, regularly dock on both sides, or tie up in a lock or against pilings, carry extras. Fenders only work where they are, and boats shift at the dock.
Step 3: Choose the right type
- Twin-eye cylindrical: the most versatile. Eyes at both ends let you hang them vertically or horizontally, which is ideal along pilings.
- Center-hole (rope-through): line runs through the middle, good for horizontal hanging.
- Heavy-duty (HTM style): thicker walls and inflation valves for larger, heavier boats.
- Round (ball) buoy fenders: great for bows, sterns, rafting and big boats against hard docks. Also used as mooring buoys.
- Pontoon fenders: shaped to fit pontoon tubes.
- Flat fenders: sit tight against the hull and will not roll, useful in tight slips and on high-freeboard boats.
Step 4: Inflation and care
Inflatable vinyl fenders work best firm but not rock hard. Over-inflated fenders transmit shock and can burst in hot sun. Many fenders come with an air adapter or valve so you can adjust pressure with a pump. Rinse them with fresh water and clean scuffs with a vinyl cleaner.
Step 5: Protect your gelcoat with covers
Bare vinyl fenders pick up grit and can leave marks or wear dull spots on gelcoat as the boat moves. Fender covers slip over the fender, cushion contact and stop scuffing. They also make fenders look sharp and hide fading.
Step 6: Hang them right
- Hang fenders so the widest part meets the dock or the other boat at the contact point, usually just above the waterline at the widest beam.
- Use proper fender line, at least 3/8 inch for small boats and larger for big fenders, tied with a clove hitch to a cleat or rail.
- Bring fenders aboard before getting underway. Dragging fenders is a giveaway and wears them out.
- For pilings, hang fenders horizontally or use a fender board.
Our picks by boat size
All in stock at Boat Supplies Direct.
Small boats, skiffs and jon boats (under 18 ft)
Polyform G-2 Twin Eye Fender (4.5 x 15.5 in).
Center consoles, bowriders and bay boats (18 to 25 ft)
Polyform G-4 Twin Eye Fender (6.5 x 22 in) with air adapter, or the heavier Polyform HTM-1.
Express cruisers and larger center consoles (25 to 35 ft)
Polyform G-5 Twin Eye Fender (8.8 x 26.8 in).
Big boats and rafting
Polyform G-6 Twin Eye Fender (11 x 30 in), and Polyform A-2 Round Buoy for bows and rafting.
Pontoons
Dock Edge 'TOON Pontoon Fender, 36 in.
Fender covers
Master Fender Covers for HTM-3, Master Fender Covers Double Layer for HTM-4, or Polyform Elite Fender Cover for G-5 and HTM-2.
Frequently Asked Questions
What size fenders do I need for my boat?
Plan on about 1 inch of fender diameter for every 4 to 5 feet of boat length, and go one size larger for heavy boats or exposed docks. A 25-foot boat typically uses 6.5 to 8 inch fenders.
How many fenders should I have?
At least three per side for boats up to 30 feet, plus one for every additional 10 feet. Carry extras if you raft up or dock against pilings.
Should fenders hang vertically or horizontally?
Vertically against flat docks and other boats. Horizontally against pilings, where a vertical fender would roll off.
Do I need fender covers?
They are strongly recommended. Covers prevent scuffing and dull spots on gelcoat and extend fender life.
How much air should be in a boat fender?
Firm but with some give when squeezed. Over-inflated fenders transmit shock and can burst in heat.
What is the difference between G-series and HTM fenders?
Both are twin-eye cylindrical fenders. HTM fenders have thicker walls and are designed for heavier boats and harder use.
This guide is general information. Fender needs vary with boat weight, dock type and conditions, so size up when in doubt.
