How long should boat fenders be for my boat?
I've got a 32ft sailing yacht on a floating marina pontoon, with four cylindrical fenders about 50cm long. Are these long enough, and should I replace them with longer ones or thicker ones?
Answer
For a typical 25 to 35ft leisure boat, start with cylindrical fenders roughly 50 to 65cm long, increasing to around 70 to 90cm for many 40 to 50ft boats. Check diameter and the height of the pontoon's rubbing edge first: a long, thin fender can still squash flat or leave the wrong part of the hull exposed.
Check the hull's contact points
Start with the boat alongside its usual berth. Find the pontoon's rubbing edge and the part of the hull closest to it, usually around the boat's widest section. Check that the existing fenders stay between those surfaces as the boat moves.
A fender needs enough usable body above and below that contact point to allow for normal rolling, loading changes and wash. The tapered ends and attachment eyes offer less protection than the full-diameter middle, so overall length alone can be misleading.
A floating pontoon generally rises and falls with the boat, keeping the contact height fairly consistent. Against a fixed quay, that height changes with the tide. Longer fenders alone will not solve every arrangement, particularly alongside piles or projecting stonework.
Cylindrical fender sizes
These starting ranges suit conventional inflatable cylindrical fenders on leisure boats in reasonably sheltered berths. Dimensions are approximate diameter × overall length; manufacturers' measuring conventions vary.
- Up to 20ft: around 12 to 15 × 40 to 50cm.
- 20 to 25ft: around 15 to 20 × 50 to 60cm.
- 26 to 32ft: around 20 to 25 × 60 to 65cm.
- 33 to 40ft: around 25 × 65 to 75cm.
- 41 to 50ft: around 30 × 75 to 90cm, often supplemented by larger round fenders.
These are not load ratings. A heavy cruising yacht, broad motor cruiser or exposed berth calls for more cushioning than a light boat of the same length. When choosing between similar lengths, extra diameter is often more useful because it increases the separation between hull and pontoon.
The Hallberg-Rassy 48 Mk I equipment specification, for example, lists six fenders: two 10 × 25in and four 12 × 30in, approximately 25 × 64cm and 30 × 76cm. A substantial yacht may therefore carry a mixture of sizes rather than six identical fenders.
Set the fender height
For ordinary pontoon berthing, hang cylindrical fenders vertically with their full-diameter bodies spanning the pontoon's rubbing edge. Keep the lower ends just clear of the water where the contact height allows. Dragging them in the water encourages fouling and can make them lift or roll out of position.