How many fenders does your boat need, and what size?

Fenders are the cheapest insurance aboard — provided you carry enough of them, in the right size. Undersized, they flatten at the first cross-wind gust; too few, they leave metres of hull exposed.

How many?

The usual rule: one fender every 2 to 2.5 metres of exposed hull, with a minimum of three per side.

Boat length	Per side	Recommended total
< 8 m	3	6
8 – 11 m	4	8
11 – 14 m	4 to 5	8 to 10
> 14 m	5 to 6	10 to 12

The total assumes you can rig both sides — essential when rafting, in waiting basins, or when your assigned berth changes at the last minute. That’s also why hangers sell in packs: FENDLOCK comes as a single unit or in packs of 6, 8 or 10, one pack for each boat size.

What size?

The common yardstick for cylindrical fenders: about 2.5 cm of diameter per metre of boat length. A 10-metre sailboat calls for fenders around 25 cm in diameter — size F4 with most manufacturers.

F1 / F2 (13–15 cm): tenders, small sailboats, light motorboats
F3 (18–20 cm): 7 to 9 m
F4 (21–23 cm): 9 to 12 m
F5 and up (30 cm+): 12 m and beyond

Slightly too big beats too small: a fender works in compression, and its volume reserve is what absorbs the shock of a gust slamming you against the quay.

Cylindrical or round?

The cylindrical fender is the Swiss army knife: it protects along its whole length and adjusts easily in height. The round fender takes far higher loads — useful at the beam of larger yachts or when rafting — but is bulky to stow. Most cruising boats sail with cylindricals, plus perhaps one round fender as backup.

Weight — a detail that isn’t one

An F4 weighs 3 to 4 kg wet. Your hanging system must hold that weight without slipping — FENDLOCK is tested up to 5 kg, covering sizes F1 to F4 with margin.