Benny,
I am afraid that in terms of vessel construction and size there is no such thing as a "coaster". The term "coaster" was traditionally used in Northern Europe to describe ships whose certificates limited them to particular trading areas, such as Elbe - Brest. It really has little do do with their construction or size as some 400-500 tonne ships traded to West Africa or Eastern Med whilst some 10,000 tonne ships were restricted to coastal limits.
Apart from a few craft engaged in special trades, it is unlikely that the smaller cargo ships of today have such limits imposed on them as they are usually classed for World Wide trade to provide maximum flexibility for their owners.
Brgds
Phil