The wheel bearings are the most important maintenance item on your trailer. Every time you launch your boat, the trailer axles and wheel bearings are submersed in water at least twice. Trailer bearings get warm when trailered, and when they are submersed in the water they immediately are cooled down. This quick cooling process creates a vacuum inside the bearing housing and causes water to be pulled inside the bearings. This is a natural occurrence that is unique to boat trailers. After repeated launches the water eventually washes the grease out of the bearings. This is why it is very important to replace the bearing grease on a regular basis. Make sure you use good quality heavy-duty bearing grease. Many trailers have zerk fittings installed on each wheel bearing for the purpose of regularly adding grease. If your trailer does not have zerk fittings, then remove the bearing cap and manually add the grease. You can add a "bearing buddy" with zerk fittings to each bearing. For more information on this option go to www.bearingbuddy.com.