Sorry to ask such a basic question, but can I just clean my hull and paint on a layer of anti-foul or do I need all sorts of layers, primers, thinners etc etc?
What type of A/F was on before and what you are using i.e. hard on top of ablative might not work, just as some manufacturers potions are not too happy on top of other brews, but normally its ok. If in doubt you can either scrape of the existing layers or use a primer coat.
Personally, I just gave it a sand with coarse paper and then slapped the paint on.
As Talbot says but DONT forget to wear a mask, A/F is pretty lethal if sanding.in fact its not good for you when pressure washing as the water vapour carries the A/F in it.
In the old days antifoul was indeed lethal - anyone remember the weals that Kobe would raise on your skin? - but I should think that, judging by the effect that it has on marine life, you would be quite safe to drink the modern stuff.