In the areas where road transport is not possible, the boats trailers are used as the carrier for transporting goods from one place to the other. The critical difference between the seals used in boat trailers and the road trailer seals is that the material that is employed in boat trailer seals should be water repellent specifically an alloy. These seals prevent water and dirt from entering the trailers hub, thus causing premature bearing failure.  Generally they should be inspected frequently before and after trailering.  If you see signs of grease or oil on the inside of the trailers rim, they need to be replaced. Some of the commonly employed boat trailer seals is oil and grease seals. These seals are circular in shape with bearing placed inside the ring to facilitate the movement of boat and the attachment. It acts as a coupling device which is water repellent and ideal for using in moisture rich surrounds without and damage.