I am currently working underneath my boat..it has had several coats of paint put on it...not to a good a standard,and while ppreparing it to take on a decent finish..i have been sanding variouse different areas to make smooth and have found that the filler used over some of the screws has deteriated ..my question is what type of wood filler do i use ? the panels are all secure..and the boat is watertight...i will be repainting it once all nice and smooth...Thanks in advance...

There's folk on here more qualified than me to answer this but just to add to the debate:-
In the last few years Ive been using epoxy resin (SP systems Ampreg in my case but others swear by Wests) thickened with colloidal silica or microfibres. Wet the surface first with neat resin just to get it to soak in and provide a good key then apply the thickened epoxy. Don't go too mad with it mind, it's harder to sand than polyester type fillers.

Thats great..Thank You.