Longshoremans Insurance refers to USL&H Coverage. USL&H is the United States Longshoremans & Harbor Work Act and is sometimes eferred to as the Longshore Harbor Workers' Compensation Act - LHWCA.
The USL&H Act was put in place to provide compensation to workers if they were injured or killed while working on navigable waters in the US, including any adjoining pier, wharf, dry dock, terminal, building-way, marine railway or other adjoining area customarily used by an employer in loading, unloading, repairing, dismantling or building a vessel.
Over time, the term "navigable waters" has grown to include practically any body of water. If your company does work on or near the water, even if you're a diver, a repairman, or an equipment supplier, chances are standard Workers Compensation will not cover you should your employee have an accident in a maritime environment.