It's an old thread but I thought I would add my experience of the Rockpile - I won't forget it!
Heading south singlehanded in an old Bristol 30 sailboat with 4'-6" draught we were making good progress at 6 knots in 13 feet of water
and not long into the Rockpile and about half tide.
I eased to starboard to pass a northbound yacht and still within the day marks when BANG
we bounced up a few inches and BANG BANG BANG
we bounced over the rock shelf still making a good speed.
Once in deep water again I sheered to port behind the yacht now passed and waved at their shocked expression that I was ok ( I hoped! )
Throttled back and nipped below to check the bilge
and all ok. I couldn't spend much time checking as we were still in the narrow Rockpile channel.
still seemed to be attached to the long keel
and working ok so continued for a few minutes more and then quickly checked the bilge
again - still the same level (there is always an inch in the bilge).
Frightened the pants off me!
Much later I swam down and checked the keel
. Bottom paint
(antifouling paint) was missing in places but there still seemed to be plenty of fibreglass left. We had just bounced over the 4'-4" deep shelf.
Moral of the experience - I should have passed really
close to the other yacht and not been lulled into the security
of 13 feet of water on the sounder and visually well within the channel markers..