The navigator's action is moving another player 2 tiles for 1 action - it does not specify once per turn. Does this mean he could move another player 3 or 4 tiles for 2 action points, or is there a rule/clarification about this?
According to the rulebook:
The Navigator may move other players up to 2 adjacent tiles per action
As it states it's per action so yes you could repeat that same action 3 times. It's a very useful ability.
I interpreted the rules that way, since other player abilities like the Explorer are not limited that way. When we play, a navigator can use her ability multiple times per turn.