When back on the boat I'll have to drill some holes through the laminated part of the cockpit table (for orientation: looking through the hole you'd be able to spy into the compartment in the cockpit table, or: if you're small enough to fit into the compartment and look outside, you'd see people's knees when they're seated around the table :-)).
Optimally, I'd have the right screws with me. Is anyone on their boats and can take a measurement? I'm assuming 3 to 5 mm maximum, maybe?
In my case it is 2 plies of grp with a little space in between. Both layers together far more than 5mm, but i don't remember how much it was!