The boat usually gets all the attention. The trailer underneath it sits in salt water at every ramp, and it is often the first thing on the rig to actually fail.
Owners who keep a boat in South Florida put real money and attention into the gelcoat, the canvas, the stainless, and the teak. The trailer underneath the boat gets almost none of it. It sits in the same saltwater at every ramp, towed over the same humid roads, and parked outside in the same sun, and it is usually the first thing on the whole rig to actually fail. Not cosmetically. Mechanically. A seized bearing or a corroded brake line does not care how nice the boat above it looks. The trailer takes a worse beating than the boat does A boat's hull is designed to sit in water. A trailer is not. Every time it backs down a ramp, the wheels, hubs, springs, brakes, and frame go underwater or get soaked in salt spray, then come back out into South Florida heat and humidity that almost never lets anything fully dry. That wet-dry cycle, repeated at every outing, is what actually does the damage. Salt left behind after the water evaporates is hygroscopic, meaning it keeps pulling moisture back out of the air even on dry days, so a trailer left alone after a trip is never really starting from dry. Why it is galvanic corrosion, not just rust Most trailer owners picture corrosion as plain rust and treat a coat of paint as the fix. The more damaging process on a trailer is galvanic corrosion, which happens when two different metals are in electrical contact with each other in the presence of an electrolyte, and saltwater is an excellent electrolyte. A steel axle bolted to an aluminum wheel, a steel bracket against a stainless bolt, or a zinc-plated fastener against bare aluminum all set up a small electrical cell. The less noble metal corrodes faster than it would on its own, often from the inside of a joint where you cannot see it starting. This is why a trailer can look fine on the surface and still have a hub, bracket, or axle that is failing underneath. Wheel bearings are usually the first thing to go Bearings take in water almost every time the hub gets submerged and then cools back down, because the air inside the hub contracts and can draw moisture in past the seal. Left alone, that moisture turns the grease milky and eventually lets the bearing itself pit and corrode. Spring-loaded bearing protectors help by letting you pump fresh grease in until it purges old, contaminated grease out the back, but they are a maintenance aid, not a substitute for actually checking the bearings. On a trailer that gets used regularly in saltwater, hubs should be pulled, inspected, and repacked with marine-grade grease at least once a season, and sooner if you ever see milky grease at the hub cap or hear or feel anything different in the wheel while towing. Brakes corrode where you cannot see them If the trailer has brakes, the actuator, the cables or hydraulic lines, and the brake assembly itself are all sitting in the splash zone every time the trailer launches. Surge brake actuators are especially prone to internal corrosion because they are designed to be submerged, but that does not make them immune to it. Drum brakes trap water and salt inside the drum, where it sits against the springs and hardware long after the outside of the trailer looks dry. A brake that drags, grabs unevenly, or does not release fully is often a corrosion problem before it is anything else, and it is worth having the brakes actually inspected on a schedule rather than waiting