Boat Fender Size and Placement Guide

What Boat Fenders Actually Do

Boat fenders are cushions — typically cylindrical or spherical — made from PVC or similar materials that hang between your boat's hull and the dock, jetty, pontoon or another vessel alongside. They absorb and distribute the energy of contact, reducing the risk of scratches, gel coat damage, impact marks and dent damage to the hull and topsides. They do not prevent all contact — they manage it.

Fender effectiveness depends on correct sizing, correct quantity, correct positioning and the fenders being properly inflated. A small fender hung at the wrong height, or a fender that has lost pressure over time, cushions contact significantly less effectively than one that's correctly set up. Browse the full range of boat fenders at Marine Depot.

Choosing the Right Fender Size

Fender size is the most important decision. A fender that's too small for your boat will compress completely under load and allow hard contact between hull and dock — the fender ceases to function as a buffer once it's fully compressed.

Fender sizing is generally guided by boat length, with manufacturers publishing sizing recommendations based on length overall (LOA). As a practical starting reference, a commonly used rule of thumb is one inch of fender diameter per foot of boat length — so a 20-foot (6-metre) boat would use fenders of approximately 20cm diameter as a starting point. However, this is a general reference only and the right size also depends on your boat's beam (width), hull shape, the docking surfaces you use, and typical wind and current conditions at your berth. Heavier, wider boats generally benefit from larger or additional fenders.

Check the fender manufacturer's sizing recommendations for your boat's length and beam rather than relying on any single rule of thumb. For pontoon and marina finger berth use, manufacturer guidance for specific fender products provides the most reliable sizing direction.

How Many Fenders Do You Need?

A minimum of three fenders is a common starting point for most trailerable and day boats — one forward, one aft and one at the widest point of the hull (typically amidships). For longer boats, more fenders distributed along the length of the hull are appropriate. For marina berths with rough or irregular surfaces, additional fenders give added coverage.

Carrying one or two spare fenders is also worth considering — particularly for boats that travel to unfamiliar locations where berth conditions are unknown. A spare fender can be deployed quickly if a docking situation requires more coverage than your standard setup provides.

Fender Height — Hanging Position

The most common fender setup error is hanging fenders at the wrong height. For most docking situations, fenders should hang so that the centre of the fender is at or slightly above the waterline contact point — typically the rubbing strake, gunwale or widest point of the hull. If fenders hang too high, the lower part of the hull is exposed; if they hang too low, fenders ride under the dock surface and contact still occurs.

Height adjustment is done via the fender line length. Use a clove hitch or other secure knot at the cleat or rail, with enough line to position the fender correctly. Check fender height each time you adjust for load, tide or a different berth surface height.

Cylindrical vs Round (Spherical) Fenders

Cylindrical fenders are the most common type for general alongside docking. They hang vertically and provide good side-of-hull cushioning against vertical surfaces like pilings and jetty faces. They work best when the dock surface is relatively flat and vertical.

Round (spherical or ball-type) fenders are better suited to corner positions — bow, stern or situations where your boat may swing and approach at an angle. Their spherical shape allows them to work in multiple contact directions. Spherical fenders are also commonly used for bow-to-bow or hull-to-hull contact situations. Browse dock fenders at Marine Depot.

Gunwale Trim and Rubber Rub Rail

Gunwale trim (also called gunwale rub rail or rub strake) is a continuous protective strip fitted along the hull's widest contact line. It adds ongoing bump cushioning rather than the situational cushioning of deployable fenders — particularly useful against minor contact with jetty edges, pontoon sides and other vessels in close quarters.

Gunwale trim complements rather than replaces deployable fenders for most docking situations. Browse boat gunwale trim at Marine Depot.

Fender Covers

Fender covers are fabric sleeves that fit over cylindrical fenders. They can help reduce UV exposure on the fender, reduce marking from dirty jetty surfaces where the product is suited to the surface, and add an aesthetic finish. If your berth has surfaces that transfer grime or oil to your fenders (and subsequently to your hull), fender covers help keep things cleaner. Browse fender covers at Marine Depot.

Inflation and Maintenance

PVC fenders are hollow and inflated with air. Correct inflation is important — an underinflated fender is softer but may compress too easily under load; an overinflated fender is harder and may transfer more energy rather than absorbing it. Check fender pressure periodically and re-inflate as needed using a fender pump or suitable needle inflation adapter. Inspect fenders regularly for cuts, punctures, UV crazing or valve leaks. A fender that cannot hold air needs replacing.

Fender Lines and Tying Off

Fender lines should be tied to a cleat or rail with a secure knot. A clove hitch is the standard fender knot — quick to tie, adjustable and secure. Fender lines should be of appropriate length to position the fender correctly at the docking contact point. Fender whips (short pre-tied fender lines with a loop at the top) simplify rigging and are worth considering if you're regularly adjusting fenders at different berths.

Fenders for Different Australian Berth Types

Marina pontoons, timber jetties, concrete seawalls and swing moorings each present different contact risks, and thinking about your typical berth alongside your boat's size helps you choose a genuinely suitable fender setup. Floating pontoon berths generally involve gentler, more predictable contact than a fixed jetty affected by tidal range, where the boat's height relative to the jetty edge changes throughout the day. Boaters who regularly visit unfamiliar marinas benefit from carrying a slightly more flexible fender setup — adjustable hanging heights and a spare fender or two — since berth configurations vary considerably between locations.

Matching Fenders to Hull Material

Fibreglass, aluminium and timber hulls all respond differently to repeated contact, and considering your hull material alongside fender selection is worth doing. Aluminium hulls can show scuffing or marking from repeated fender contact more readily than gelcoat in some cases, so checking fender cover material and considering additional coverage at common contact points can help maintain your hull's appearance over time. This is a cosmetic consideration alongside the primary function of cushioning contact.

Common Mistakes With Fender Setup

Beyond size and quantity, common practical mistakes include hanging fenders at a fixed height regardless of tide (leaving them ineffective at low tide or dragging in the water at high tide), using old, hardened or sun-damaged fenders that have lost their cushioning effectiveness, and failing to adjust fender position when docking on a different side than usual. Building a habit of checking fender height and position each time you dock, rather than assuming a fixed setup works everywhere, helps ensure they're doing their job.

Storage Between Uses

Fenders left inflated and exposed to direct sun for extended periods can degrade faster than those deflated and stored out of UV exposure when not in use. For boats not used regularly, checking fender condition before each outing — looking for cracking, hardening or loss of inflation — helps catch degradation before you're relying on a compromised fender at the dock. Some boaters partially deflate fenders for storage to reduce UV stress on the material and save deck space.

When to Replace Fenders

Fenders showing significant surface cracking, permanent deformation, or that no longer hold air reliably have likely passed the point where they cushion contact effectively, and continuing to rely on them provides less protection than their condition might suggest. Checking fenders at the start of each season, alongside other routine dock and mooring gear checks, is a sensible habit rather than waiting for an obvious failure.

Fenders for Rafting and Multi-Boat Situations

Rafting alongside another vessel, common at some events or busy anchorages, places different demands on fenders than standard dock use, since both boats' movement contributes to contact rather than just your own boat against a fixed structure. Carrying additional fenders for rafting situations, and checking with the other vessel's owner about fender placement before tying up, helps improve the cushioning setup for both boats during this kind of temporary, close-contact mooring.

Fender Boards for Piling Berths

Berths against timber pilings, rather than a flat pontoon or jetty edge, sometimes benefit from a fender board — a horizontal board spanning between two fenders — which spreads contact across a wider area and helps reduce the chance of fenders riding up or slipping between pilings. If you regularly berth against pilings, checking whether a fender board suits your specific setup is worth considering alongside standard fender selection.

Choosing Fender Colour and Appearance

While fender colour doesn't affect function, many boaters consider it alongside practical selection criteria, choosing colours that complement their boat's hull colour or fit with marina aesthetic expectations at their specific berth. This is a matter of personal preference that can be factored in once you've established the correct size, quantity and style for your practical needs.

Shop Boat Fenders at Marine Depot

• Boat Fenders — full range
• Dock Fenders
• Gunwale Boat Trim
• Fender Covers
• Mooring & Dock Lines

Related guides: Anchoring & Mooring Guides | Dock Lines and Mooring Rope Buying Guide | Anchor Rope vs Chain Guide