The inscription on the drawing concerns the effects of light and shadow on the water, a phenomenon illustrated in the drawing. Van de Velde writes:
ogh - op - neer dipsels ick heb dit gesien in leeffe dat het leeffe lighter was als in het water en het bruijn in het water ligh- ter d schadú bruijnder als boven úijt geseijt d úijttersten dipseties ofte een dúffeltie
[eye - up - down darkenings I have seen this from life, that in nature when the light fell in the water the brown in the water ligh-/ter while the shadow [on the ship] above was darker mention the outer darker colours or duffel]
He describes the optical illusion whereby the reflection of a ship in the water sometimes appears lighter than the ship itself, and sometimes darker. The allusion to 'duffel' refers to the dark coarse woollen material manufactured in the eponymous town in Belgium, after which the duffle coat is named.
Other drawings with similar inscriptions are in the National Maritime Museum (see M.S. Robinson, Van de Velde Drawings: A Catalogue of Drawings in the National Maritime Museum made by the Elder and Younger Willem van de Velde, Cambridge, 1958; an example is no. 742, Three sketches showing the effect of the wind on the smoke from a gun).