I've used the Fig of 8 knot as per John on all my boats and it works fine, but I've found that on the 17 I dont have to have a fig8 knot.
The reason a Fig of 8 helps (when the knot is to the back) is that when you pull the haylard, the ring not only lifts, but the top of the ring is actually pulled away from the mast as the rope going tight pulls THRU the eye and not up.
Difficult to accuratly explian, but the F8 know will help.
Another tip is to also bend the hook a little at the tip to port or Stbd and then turn the mast the other way as this also makes it ewasier to get off.
Another tip as above is to pull down on the clew at the same time to assist the hook coming off..
also, another top, is the hook at the top of the mast too long (compare with others before changing)