Why Trailer Maintenance Matters More Than You Think

There is a particular sinking feeling that comes with watching a wheel bearing fail on the hard shoulder of a busy A-road with a six-metre RIB behind you. The boat has been serviced, the engine has fresh oil, the electronics are immaculate — and the trailer, which carries the entire outfit at 60 mph through rain and salt spray, has not been touched since last summer. For UK boat owners, the trailer is often the most neglected and most heavily loaded part of the whole package.

A properly maintained trailer protects your boat, your car and everyone else on the road. It also keeps you legal: in the UK, any trailer with a maximum gross weight over 750 kg must have its own braking system, the combination must stay within the plated weights of both the trailer and the towing vehicle, and your driving licence entitlement has to cover the total mass. Trailers also have their own speed limits — 60 mph on motorways and dual carriageways, 50 mph on single carriageway roads, and 30 mph in built-up areas unless signs say otherwise.

Bearings: The Weak Point in Every Trailer

Trailer wheel bearings lead a hard life. They sit underwater on a slipway, take a battering on potholed lanes, and then run hot for hours on the motorway. The most damaging moment comes after a long tow, when a hot hub is dunked into cold sea water: the air inside the hub cools and contracts, drawing water past the seals.

Check bearings before every trip of any distance, and repack or replace the grease at least annually.

• Jack the trailer up and spin each wheel — listen for rumbling or grinding and feel for roughness.
• Rock the wheel from top to bottom to detect lateral play.
• Look behind the hub for grease weeping from a failed seal, and check the colour: milky grease means water has got in.
• Fit new seals whenever a hub comes apart, and use the correct marine-grade grease.
• Where practical, let hubs cool for twenty minutes before backing down the slipway.

Brakes and Couplings

Braked trailers use an overrun system: as the towing vehicle slows, the coupling head compresses a damper and pushes a rod that applies the trailer brakes. Every part of that chain needs attention.

• Push the coupling head in by hand — it should move with firm resistance and spring back smoothly. A soggy or seized damper needs replacing.
• Check the brake cables and rod for fraying, stiffness and correct adjustment, and confirm the handbrake holds the trailer on a slope.
• Inspect brake shoes or pads for wear and for grease or oil contamination, which ruins braking performance even when there is plenty of lining left.
• Rinse brake drums and backing plates with fresh water after a saltwater launch to slow corrosion.
• Clip the breakaway cable to a dedicated fixing on the towbar. Never loop it over the tow ball, where it can slip off. Trailers under 750 kg generally use a secondary coupling instead.

Tyres, Wheels and Load Ratings

Trailer tyres usually fail through age and standing rather than tread wear. Check the four-digit date code on the sidewall: the first two digits are the week and the last two the year of manufacture. Replace them at around five to six years, or sooner if you see cracking, bulges or flat spots.

• Set pressures when the tyres are cold, according to the trailer's laden weight rather than the car's handbook.
• Make sure the load rating is up to the job — trailer tyres are often run at pressures well above those of a typical car tyre.
• Re-torque the wheel nuts to the specified figure and check them again after the first twenty miles of a journey.
• Carry a spare wheel, a jack that actually fits the trailer, and a wheel brace of the right size.
• Check rims for corrosion and cracks, particularly around the stud holes.

Lights, Wiring and Paperwork

Lighting faults are the most common reason for a trailer to attract unwanted attention. Before you set off, walk around the outfit with the sidelights, indicators, brake lights and fog lamp operating.

• Check the plug and socket for corrosion and bent pins, and look at the cable where it enters the plug — that is where wires break.
• Make sure the number plate on the trailer matches the towing vehicle and that it is illuminated.
• Confirm reflectors, side marker lamps and any rear marker boards are intact and clean.
• Check the trailer's identification plate is present and legible, showing its maximum gross weight.
• Remember that the towing vehicle's mirrors must give you a clear view past the boat; extension mirrors may be needed.

Hitching, Launching and the After-Tow Routine

Aim for a nose weight of roughly five to seven per cent of the trailer's total weight — commonly 50 to 75 kg — and check that the car is not squatting at the rear. Secure the boat with proper ratchet straps over the hull or at dedicated tie-down points, make sure the outboard or sterndrive is supported, and stow any loose gear. Adjust the car's own tyre pressures for the extra load before you leave.

After a day on the water, rinse the trailer thoroughly with fresh water — chassis, brakes, bearings, lights and wiring — while the salt is still wet. Lubricate the coupling and moving parts, and leave the trailer slightly nose-up so water drains away. Once a year, or before any long tow, have the brakes and bearings inspected properly with the wheels off. A trailer that is looked after will outlast several boats; one that is ignored will let you down on the slipway, or somewhere far worse.