Have a mate who has just purchased a Van der stadt 40 with eventual plans to race, coming from a dingy/cat sailing back ground the use of backstays seem a little odd. The boat has 5 backstays the main one thats obvious, the it has upper and lower stays that run to blocks and winches to the stern, the main one that I understand how ever what is the theory behind the others, can anyone enlighten me

when going down wind especially make sure you have a fair bit of tension on the running backstay (or runners)(the one which opposes the forestay) this will prevent you from losing a rig in 20+knots. this is the most important.
the backstay which ataches to the top of the mast is used to control mast bend and change the shape of the main. basically let it off in light winds and as the wind strength increases pull it on to help depower the main.

Whats the name of the Vandestat 40 your mate has bought.My old man had one about a year ago named War Lord. They were a pretty quick boat in their day.

Thats cool. The old man has some realy nice pictures of Warlord when it was nice and new in the Sydney Hobart,I'll see if I can get hold of them and put them up here.
Now I think a bit more it was probably 2 or 3 years since he had it because he sold it to someone in Melbourne or Sydney and I think they got into a bit of grief sailing it back(was on the news etc)
Let me know if you want anymore info on it , I may be able to get some good info for you.