Lewis Morris' early chart of Ramsey sound shows the Bitches and Whelp reef extending into the sound from Ramsey Island. The Admiralty Sailing Directions of 1870 describe them as 'a curious ledge of high rocks, extending at right angles from the middle of the east side of the island for about 2 cable lengths into the Ramsey Sound. A few low rocks, 10 or 12 yards outside its outer end, cover at the first quarter flood.' The tide speeds up as it is funneled through the relatively narrow channel of the sound and the reef then acts as a dam. The tides run north for approximately 6 hours on the flood and south for 6 hours on the Ebb. The tidal race in the Sound can reach speeds of up to 8 knots on a spring tide and over the reef itself in places this can increase to 18 knots.This effect is particularly spectacular during the flood tide when the water level on the south side of the rocks can be as much as 1.5 meters higher than that on the north side.

Sources include:
Morris, L, 1748, Plans of Harbours, Bars, Bays and Roads in St George's Channel, plate 21

Maritime Officer, RCAHMW, April 2014.