If you are a stream, or moving water fly-fisher then I know you understand lag in your line and that lag is created by the flowing or moving water. The same can, and in the right situation, should be created while fishing in your float tube.
First… How … You need to put the bank on your left side (right handers) and while fishing in reverse (kicking backwards with fins) you will be moving and thus the point at which you cast will change as you move parallel with the shore. As you do this you are now creating lag or a bow in your line just like you would in moving water.
Second… Why … By creating lag or a bow you can move and cover much more water than if you were sitting still. As you retrieve, rod tip at or below the surface, stripping your fly and while moving backwards keep the rod tip pointed and moving slightly toward the closest point of the bow you have created. By doing this you will be ready for a strike and then can give a quick strip set to embed the hook securely in the fishes lip. If you retrieve the fly without a strike, you can move your attention further left or up the shore to the next likely spot at which you now make another accurate cast and repeat the above steps…all while moving backwards around the perimeter of the lake. When I’m using a floating line and a streamer I often interrupt the strip by throwing a directional mend…either to my left or right causing the streamer to make a sharp right hand or left hand turn and once again increasing your chances of getting a strike.
So…if you feel like moving…by all means do so and you will find you can cover more water and be more functional at the same time.