What size fenders should I use for a pontoon boat?

For most 20 to 24 ft pontoon boats, start with cylindrical fenders about 8 inches (200 mm) in diameter and 20 to 27 inches (510 to 690 mm) long, with three along the docking side. Choose larger fenders for heavier boats or regular wake, and check the dock's contact height first: each fender must protect whichever part touches first, usually the projecting deck edge or an aluminium pontoon tube.

Check the dock contact points

Before buying, bring the boat alongside in calm conditions and identify the contact points. Pontoon boats have a wide deck above rounded tubes, so a fender that works on a conventional hull may hang in the gap beneath the deck and offer little protection.

Check the height of the dock edge and any projecting bolts or brackets, then establish whether the deck trim or tube would strike first. Measure with the boat carrying its usual passengers and gear; loading changes the deck's height above the water.

A floating dock usually stays at a fairly consistent height relative to the boat. A fixed jetty needs enough vertical fender coverage for changing water levels, while widely spaced piles may need a fender board to bridge the gap.

Keep hands and feet out of the gap between boat and dock while checking clearance.

Choose diameter and length

These sizes are practical starting points for leisure pontoon boats in reasonably sheltered berths, rather than a universal manufacturer's rating:

• Up to 18 ft: cylindrical fenders roughly 6 to 6½ inches (150 to 165 mm) in diameter and 18 to 23 inches (460 to 580 mm) long.
• 19 to 24 ft: roughly 8 inches (200 mm) in diameter and 20 to 27 inches (510 to 690 mm) long.
• 25 to 30 ft, heavier tritoons or exposed berths: roughly 10 inches (250 mm) in diameter and 25 to 30 inches (635 to 760 mm) long; consider a 12-inch (300 mm) diameter where conditions justify it.

Diameter provides the stand-off and compression distance. A long, thin fender can cover the right height yet flatten enough for the deck trim to hit the dock. If passing wakes regularly push the boat sideways, move up a diameter rather than buying a longer fender.

Boat weight, windage and berth exposure matter as much as length. A heavily loaded 24 ft tritoon with a large canopy may need the larger size. Check the manufacturer's size guide too, because nominal dimensions and recommended boat lengths vary.

Match shape to contact surface

Conventional inflatable cylindrical fenders work well when they sit securely between the dock and a supported contact surface. Hang them vertically against a continuous dock face. Horizontal positioning can suit a low dock edge, provided both ends are secured to stop the fender rolling away.