Let’s continue with the example that the whirlpool caused the barrel to go out and hit the left wall.

The lower cannons can still be loaded using the regular loop method.

(Be careful loading the cannon closest to the barrel – when new pieces come out they could head straight towards the cannon you’re loading and get in the way.)

All you need to do to fill the upper cannons is to create a second loop that crosses just those two guns. 

Place an arrow pointed up at then upper right corner of the bottom loop, then place another arrow pointed left to send the pieces traveling along for a second loop.  Once the second loop is formed, the upper cannons can be easily loaded. Fortunately this board will allow both loops.

This board, however, will not.  You can still handle the lower cannons with a loop, but no loop can be created to travel past both the upper cannons. 

To load the upper right gun just use the same method shown earlier when I dissected the one-arrow two gun board.  You must be more careful though – pieces coming out of the barrel could hit other pieces, and something might slip into your cannon.

For the upper left gun, a one cannon loop might be best.  Be careful about your timing, and direct the pieces into the corner, then create a loop that keeps them by that cannon.