The Sandship is one of the later dungeons in Skyward Sword and is the second, after the cistern, to contain a combo door lock. This is a lock where you must slash the pieces in a certain order to unlock the door. Here is how to figure out the combo to unlock the ship wheel door lock.
You will need to first use the bellows to blow away the sand. You will find four different ship wheels underneath that will signal the direction in which you must slash the lock in order for it to be unlocked. The problem now is figuring out the orientation and the order of the slashes.
Which way is up?
So the first problem is knowing which way is up in order to know what direction to slash. The clue is with the brown part. You will see from the ship wheels on either side of the locked door that the brown/red part will face upward. This means the ship wheels buried beneath the sand in this area will be up based on which side the brown part is on.
What order are the ship wheels?
The second problem with the ship wheel locked door is finding out the correct order in which the four slashes should be performed. The clue, again is with the brown part at the top of the wheel.
You will see that the brown spokes on top of each of the four wheels are not the same. Upon closer inspection, you will see that the number of spokes colored on each is different. You now have your order.
Start with the ship wheel that has one red spoke and work up to the fourth. This is the correct order needed to unlock the combo lock on the ship wheel locked door on the Sandship.