DRAWINGS, ETCHINGS, ENGRAVINGS
Since ever and on whatever material,, humans always drew. Often used as a sketch, some of them reaching now big money, drawing can be an artwork by itself in marine art as elsewhere. Some artists even used drawing exclusively as: Coopse, Ozanne, Vernierou Roux...
Willem Van de Velde l'ancien - Battle of Lighorn
Engraving is quite common in marine art, either as a proper artwork or as reproducing a painting.
Arthur Briscoe - The Helm