Boat Trailers for Large Boats (17-23ft+)

Large boat trailers carry the most weight, tow the longest distances, and face the harshest conditions. Whether you are trailering an 18ft Stabicraft for offshore game fishing, a 20ft Surtees for the Hauraki Gulf, or a 22ft Buccaneer for serious blue-water work, the trailer underneath needs to match the investment you have made in the boat above it.

At this size, you are choosing between the top of the single-axle range (the AT 600-SR with its 100x50x4mm chassis and 10:1 winch) and the tandem axle range (Tandem 600, 650, and 700) with twin axles, heavier chassis, and brakes fitted as standard on the larger models. The choice comes down to boat weight, towing distance, and how much stability margin you want on the road.

Every large Alpha trailer is fully hot-dip galvanised, uses 20 or 28 multi-rollers for smooth launching, and is fully adjustable to suit your specific hull shape. These are not budget trailers: they are engineered for the loads and conditions that large trailerable boats demand.

Single axle vs tandem for big boats

The AT 600-SR is the top of the single-axle range and handles boats up to about 20ft with a GVM of 1,700kg. It is lighter, easier to manoeuvre in tight spaces, and less expensive than a tandem. However, tandem trailers provide better highway stability, more even tyre wear, and a critical safety advantage: if you lose a tyre at speed, the other axle keeps the trailer upright and controllable.

For boats over 18ft or those that weigh more than about 1,200kg fully loaded, a tandem trailer is the safer and more practical choice. The Tandem 600 starts at $6,550 and covers boats up to 20ft. The Tandem 650 ($7,650) and Tandem 700 ($8,050) step up to a 125x50x5mm chassis, 28-roller system, and cable disc brakes as standard for boats up to 23ft.

Braking requirements

Every boat and trailer combination in this size range will require brakes by NZ law. The AT 600-SR and Tandem 600 offer cable or hydraulic brakes as an option. The Tandem 650 and Tandem 700 come with cable disc brakes fitted as standard, with hydraulic disc brakes available as an upgrade.

Cable brakes are mechanical and reliable but require periodic adjustment. Hydraulic disc brakes offer stronger, more consistent stopping power and are self-adjusting. For heavy boats towed long distances or over hilly terrain, hydraulic disc brakes are worth the upgrade.

Heavy-duty chassis specs

The AT 600-SR uses a 100x50x4mm chassis, a significant step up from the 70x50mm chassis on smaller models. The tandem trailers go further: the Tandem 650 and 700 use a 125x50x5mm chassis with 100x100x5mm drawbar and 70x50x4mm cross members. This is structural steel, not light-gauge tubing. Combined with the 10:1 (single-axle) or 15:1 & 5:1 (tandem) Trojan winches, these trailers are built to handle the full weight of large offshore boats.

Why galvanised steel matters at this weight

The heavier the trailer, the more critical the structural integrity of every weld, joint, and chassis member. Corrosion hidden inside a box-section chassis is difficult to detect and dangerous under load. Full hot-dip galvanising coats every surface, inside and out, in a thick zinc layer that protects against salt water and coastal air for decades. At the loads these trailers carry, there is no substitute for proper galvanising.