another question is why install a garboard drain?....
I can only see the reasoning of drilling a small hole in the lowest point of a sailboat if it has extremely leaky deck fittings it is going to spend an unreasonable amount of time on the hard, untarped in a rainy area while its being repaired/refitted and all the deck leaks fixed, and then the hole is sealed closed with epoxy after it has served its purpose.....