How do I choose and use a boat trailer jack safely?

Choose a boat trailer jack or jockey wheel with a lifting capacity comfortably above the trailer's measured nose load, a mounting that suits the drawbar and enough travel to clear the towball. Use it on firm, level ground with the trailer wheels chocked, and use a separate suitable jack and axle stands for wheel changes.

Check load and mounting

Start with the trailer plate, coupling markings and existing jack label. Establish the fully loaded trailer weight and measure the nose load with the boat, engine, fuel and equipment in their normal travelling positions. Moving an anchor or filling a forward tank can change it substantially.

A drawbar jack supports the load at its mounting position, rather than the entire boat and trailer weight. A jack mounted behind the coupling carries more than the nose load measured at the towball. Allow for its position and follow the trailer maker's specification.

• Lifting capacity: the load the jack can raise. A higher static support rating does not mean it can lift that amount.
• Mounting strength: the clamp, swivel bracket, bolts and drawbar must all suit the load. A stronger jack cannot compensate for a weak bracket.
• Nose-load limits: check the permitted loads for the trailer, coupling, towbar and vehicle separately. A larger jack does not increase them.

For example, a unit rated to lift 250 kg gives useful margin over a measured 100 kg nose load on a conventional drawbar installation, provided its mounting and manufacturer's instructions suit the trailer.

Choose wheel, foot and travel

Clamp-mounted jockey wheels commonly have 48 mm outer tubes; heavier versions often use 60 mm tubes. Measure yours before ordering. Appearance is no guide. AL-KO and Knott supply common European designs, while Fulton offers marine swivel jacks. Mounting patterns and ratings vary between models.

A jockey wheel makes a small trailer easier to position on smooth concrete. A broad solid wheel copes better with joints than a narrow wheel, but gravel, sand and soft ground can stop either abruptly. Do not force the trailer sideways against a trapped wheel: this bends tubes and brackets.

A footplate jack suits trailers that need lifting and stationary support without manoeuvring. On softer ground, put a sound load-spreading pad beneath the foot or wheel. Avoid loose bricks and unstable stacks of timber.

Check both extended and retracted dimensions. The jack needs enough lift to uncouple at the intended parking spot and enough road clearance when stowed. The handle must clear the winch post, bow and brake lever. If a swivel bracket is fitted, its locking pin must engage fully in both working and travelling positions.