Begin with a clove hitch underneath the spar to be supported.
Wrap the two ends of the rope together so that the short end is trapped and the clove hitch cannot come undone.
Wrap the rope first over one spar, then under the other, pulling tight all the time.
On the second turn round, go inside the previous turn of rope on the top but outside underneath the spars.
After three turns, apply three frapping turns which pull on the rope turns already made, making them even tighter.
Finish off with a clove hitch on the opposite spar to the one on which you started.
Continue to add to the structure.
Finished structure a raft capable of floating a two fingered Kit Kat.