After using Towing Option #1 from the Reference Diagrams (initiate towing when already touching a derelict’s bow at the beginning of a move action), can you immediately drop the tow in order to not have your base move limited to S, or is your base move limited to S during that move action?
You can drop the ship at any time, even immediately after grabbing it, but the movement reduction continues to apply for the entire move action.
I’ll add that one to my notes for the future (maybe) PC update.