Owners of a yacht that is registered in the Netherlands either require that the owner resides in the Netherlands or that they appoint a ship manager.
Authorities, such as the Kadaster, require an onshore contact point in the Netherlands, in case they have matters to communicate to the owner of the boat. Yes we can see you think that with modern means of communication one can always be reached, but the authorities want an official correspondence address in the Netherlands they can reach out to.
So one of the roles of the ship manager has is to act as the representative of the boat owner(s).
Besides being the representative for the boat owner, the ship manager also has managerial- and administrative-tasks, such as :