Why are my boat fenders not protecting the hull properly?
My 10-metre yacht has three cylindrical fenders along the pontoon side, but I'm still getting scuffs and the occasional knock when wash comes through. How do I tell whether they're too small, badly positioned or incorrectly inflated?
Answer
Your fenders are probably missing the contact point, moving out of position or compressing too far under load. Check their height and spacing as the boat moves against the berth, because even large, correctly inflated fenders cannot protect a gap they do not cover.
Find the contact points
Look along the gap between hull and berth from a safe position on deck or the pontoon. Keep hands and feet clear of the gap; never try to stop a moving boat with your body.
Fresh scuffs show where contact occurs. Watch the boat in ordinary wash too: the hull may touch near its widest point at rest, then swing its bow or quarter into the pontoon as it surges.
- Floating pontoon: hang fenders so their thickest section overlaps the pontoon's rubbing edge, with enough length above and below to allow for rolling.
- Fixed quay: allow for the full tidal change. A setting that works at high water may leave the hull exposed later.
- Another boat: match fender height to the neighbouring hull's shape and rubbing strake, rather than simply matching deck heights.
Spread fenders around the likely contact points, including the vulnerable quarter. Three fenders bunched amidships leave both ends exposed. On a flared bow, a round fender often stays between the surfaces better than a narrow cylinder.
Check size, inflation and condition
Diameter provides the cushioning distance; length mainly maintains coverage as the boat moves. A long, skinny fender can still squash flat against a hard pontoon edge.
As a starting point, a 9 to 11 metre cruising boat commonly needs cylindrical fenders around 200 to 250 mm in diameter, with larger ones for a heavy boat or exposed berth. Boats around 12 metres often benefit from fenders 250 to 300 mm in diameter. Displacement, hull shape and berth conditions matter more than boat length alone, so treat these as starting sizes.
Follow the fender maker's inflation specification. Pressure varies with construction, and the fender should retain some give rather than feel drum-tight. Too little air lets it collapse; too much reduces its ability to cushion an impact and increases loads on its body and valve.
- Check for splits around the eyes, hardened material and damaged valves.
- Use soapy water to locate a suspected air leak.
- Recheck inflation after a substantial temperature change.
- Replace any fender that repeatedly loses pressure or bottoms out under normal berth loads.