Dabber or dab-toe is a member of the ships company who does, amongst other things these days, seaman-ship. When I was in, they were the Ops. Department, then changed to the Warfare Branch. What they're part of this week I don't know, but somebody will be along to edit this.
They get their name from the 'fact' that they're always painting the upperdeck, dabbing their brushes into the paint and onto the ship. So engrossed are they in this essential job, that it is said, that if you stood still, they'd paint you.