How to Get the Swift Sail
In the Auction House, you may have to quit out and re-enter a few times to get the Swift Sail to appear. It appears at random along with a Heart Piece and a few other items.
To win the auction you can use a clever trick: Place a bid 10% higher than the current bid to freeze your opponents for 15 seconds. A good technique is to place a 10% higher bid (e.g. if the current bid is 110, add 10%, or 11 rupees for a bid of 121) at the 30 second mark, then wait for someone to get un-stunned. Mash the button to place another 10% increased bid around the 10 second mark. You will win the Swift Sail for about 200-300 rupees. Hit A to activate it while sailing. It's amazing.