Based upon Supple Iron and Rigid Rope (Ars p154), this spell makes use of the Terram generic materials examples to float items like wood.
Floating Anchor and Sinking Oar
Muto Terram 15, R: Voice, D: Diameter, T: Part
Makes a buoyant object sink or a sinking object buoyant. Casting requisites of Forms appropriate to the materials affected are required.
This spell was invented by a Magus who hated swimming and loathed the idea of drowning at sea.
(Base 3, +2 Voice, +1 Diameter, +1 Part)
I took the same Base level as Supple Iron and Rigid Rope and upped the range as it’s probably more useful to make an float after it’s just gone overboard; or likewise sink. Then Target: Part so that clothes and other things can be selected on a variety of target’s. Diameter should be plenty to sink or rescue something.
All the new spells for Ars Magica can be found here.