Skiblander was buildt by the sons if Ivalde (dwarfs) on Lokis request, before he gave it to Frøya. Skibladner was just one of the gifts Loki gave the Æsir, others was Thors hammer Mjollnir, Odins ring Draupnir etc. It was not exactly as repayment for a debt, but an attempt to get on the good side of the Æsir after the history where he cut the hair of Siv (Thors wife). Half of the artifacts was made during a bet between Loki and some dwarfs, with his head as the price if he lost (he won).
Would you trust this man
http://upload.wikimedia.org/wikipedia/commons/8/82/Loki_Iceland.jpgThe old norse mythology is quite fun reading for children if you just omit the gory details.
