Why are my boat fenders leaking air, and can they be repaired?
Two of the cylindrical fenders on my sailing yacht go soft within a few days of pumping them up. There are no obvious holes, so how can I tell whether the valves are leaking, and is a repair worth trying?
Answer
Boat fenders usually lose air through a dirty or damaged inflation valve, a puncture, or cracks in ageing PVC; a drop in temperature can also make them feel softer without a leak. Check the valve first with soapy water: a serviceable valve can often be repaired, while split seams and badly deteriorated bodies usually mean replacement.
Check for air loss
Inflate the fender to the manufacturer's recommended shape and pressure, then leave it in shade at a reasonably steady temperature. It should yield under hand pressure rather than feel drum-tight. Many conventional inflatable fenders work at roughly 0.15 bar, or 2 psi, but the correct limit depends on the make and construction.
A fender pumped up on a warm afternoon will feel softer on a cold morning. Compare it at approximately the same temperature after 24 to 48 hours before deciding that it leaks. Repeated softening over several days in similar conditions needs investigating.
Use a hand pump and the correct adaptor. Uncontrolled compressed air can overinflate the fender, eject valve parts or rupture the body.
Look for a brand and model moulded into the end. Polyform, DAN-FENDER and other manufacturers use different valve arrangements, sometimes within their own ranges. A screw in the valve may form part of the seal rather than need removing for inflation.
Find the leak
Mix a little washing-up liquid with water and brush it over the inflated fender. Look for bubbles that keep growing, rather than foam left by the brush.
- Test the valve opening. Persistent bubbles here indicate a leak through the valve's internal seal.
- Test around the valve housing. Bubbles around its perimeter suggest a loose insert, damaged housing or failed joint to the body.
- Work around the body. Check scuffed areas, moulding seams and the shoulders near the rope eyes. Gently flex suspect areas to reveal fine cracks.
- Check hidden surfaces. Remove any fender sock and inspect underneath it. For an elusive leak, immerse sections in a tub and watch for a steady stream of bubbles.
Mark each leak before rinsing and drying the fender. Blackening or hardening of the material may indicate heat damage, as can distortion. A fender hanging over a diesel heater exhaust can melt and puncture.
Repair a serviceable valve
Deflate the fender before dismantling any valve components. Wash salt and grit from accessible parts with fresh water, then follow the maker's instructions for reseating the seal or replacing the valve insert.