Simon,

It seems that the hatch covers don't seal at all <img src="http://www.catsailor.com/forums/images/graemlins/crazy.gif" alt="" />.

Are the hatches flat or bent to the deck curve ?

If they are bent then remove silicone, screw hatch cover onto hatch, inspect for sealing then apply complete assembly to deck. Don't worry that it doesn't follow the deck shape. At least it will seal. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

Regards,

Peter