An axle is a central shaft for a rotating wheel or gear. In some cases the axle may be fixed in position with a bearing or bushing sitting inside the hole in the wheel or gear to allow the wheel or gear to rotate around the axle. In other cases the wheel or gear may be fixed to the axle, with bearings or bushings provided at the mounting points where the axle is supported.
Axles are integral structural components of a boat trailer. The axles maintain the position of the wheels relative to each other and to the vehicle body. Since the wheels of a boat trailer are the only parts touching the ground, the axles must bear the weight of the boat trailer plus the boat itself, as well as acceleration and braking forces of the vehicle towing the trailer. In addition to the structural purpose, axles may serve one or more of the following purposes depending on the design of the vehicle.
Braking: Conversely, a vehicle may be slowed by applying force to brake the rotation of the axle. Consumer vehicles’ brakes are part of the wheel assembly and therefore exert friction on the wheels directly, but engine braking may still be affected via the axle.
Steering: The front axle of most boat trailers is a steering axle. The trailer is maneuvered by controlling the direction of the front wheels’ rotational axis relative to the body and rear wheels.
Dead Axles
A dead axle, also called lazy axle, is not part of the drivetrain but is instead free-rotating. The rear axle of a front-wheel drive car may also be considered a dead axle. In particular, many trucks and trailers (particularly boat trailers) use dead axles for strictly load-bearing purposes.
Some boat trailers are configured with airlift axles, which may be mechanically raised or lowered. The axle is lowered to increase the weight capacity, or to distribute the weight of the cargo over more wheels, for example to cross a weight restricted bridge.
When not needed, the dead axle is lifted off the ground, to save wear on the tires and axle and increase traction in the remaining wheels. Lifting an axle also makes the vehicle tighten turns better. Several manufacturers offer computer-controlled airlift, so that the dead axles are automatically lowered when the main axle reaches its weight limit. The axles can still be lifted by the press of a button if needed.
Types of Boat Trailer Axles
Boat trailer axles can be divided into several types. By number, it’s single axle, tandem axle or tandem axle heavy duty and triple axle or triple axle heavy duty models. By structural features, it’s the straight axle.
A single axle features only two wheels, with the rest of the weight dependent upon the wheel towing it. On the other hand, a tandem axle showcases a more balanced ride where the boat trailer can stand on its own with four wheels (like most cars). As a rule of thumb, the more axles and tires you have, the less risk you have of overheating the tires during long hauls.
A triple axle (and all its other variants) are reserved for those really large cargo that even a tandem axle boat trailer couldn’t handle. Build like a truck with its six wheels, it’s the axle type that assures the most balance and heavy-duty sturdiness for even the most trying of hauling conditions.
A straight axle is a single rigid shaft connecting a wheel on the left side of the vehicle to a wheel on the right side. The axis of rotation fixed by the axle is common to both wheels. Such a design can keep the wheel positions steady under heavy stress and can therefore support heavy loads.
Boat Trailer Axle Safety and Maintenance
A lot of lightweight vehicles present problems for towing. If a guy comes in with a Honda Accord and a 3,000-pound trailer setup, you’re not going to put 300 pounds of tongue weight on the trailer or his front wheels will be reaching for the sky. By shifting the trailer’s wheel axle forward or back, a service that many marinas offer, the trailer’s tongue weight can be customized to the capacity of the towing vehicle.
Axle location becomes a function of tongue weight (10%-15%), while the center spring hanger should be approximately one-third back on the window. The center spring hanger is in the same location as the center of the old single axle. Trailer performance can be improved by moving weight forward, so moving your water tank forward should be on your project list if you want a more efficient boat trailer.
In conclusion, to maintain your axles, have the axial play of the hub bearing checked and adjusted, if necessary. With boat trailers which are driven into water or sea water, the hub bearing should be re-greased shortly after contact with the water (with the exception of waterproof hubs).