I needed some wreckage markers for Galleys & Galleons. Wreckage and survivors are included with the Peter Pig manned rowing boats. PP also do some empty rowing boats. These would be a liability in combat and would have been towed behind rather than stored on deck. I didn't have any use for them so I threw them into the wreckage to add to the sense of chaos.
The PP bits were stuck onto 40mm MDF squares. Filler was used to level the surface around the markers. You can now get perfectly adequate filler in big tubs from a 'pound' shop.
Gesso waves are added with a cocktail stick (toothpick). The flotsam is flat-moulded and isn't exactly 'in' the waves, but the detail seems to fool the eye and it looks OK to me.