I have the same boat, same year, same hole, and no earthly idea what it's for. I guess I've always assumed it was for putting something tall in there, but I've been able to live with the boat for years without having that tall thing onboard. Oh well...Anyone know why they put this hole in the shelf under the sink? This is from a 2004 Hunter 306.
Here are some under-side measurements: ~19 inches deep (cabinet front to back); ~8 inches wide (cabinet side wall to the edge of the thru-hull access below); ~13 inches tall. I suppose I failed to get the actual size of the holeI'd use something besides a waste basket...something that can be washed. Cuz food scraps are wet--or at least damp--and can be oily. If you can provide me with the dimensions--diameter and depth--I'll try to come up with some suggestions...inexpensive of course.
--Peggie