Divernet
It may look calm now, but Jack Sound is renowned for its strong, changeable currents. However, braving its turbulent waters will reward you with spectacular diving and abundant marine life, says John Liddiard

Skomer Island and the surrounding marine nature reserve is one of the most popular areas for diving in South Wales. On a good weekend, diveboats from just about every slip and beach in Pembrokeshire converge on the wreck of the Lucy on the north side of Skomer Island.
But to get there you have to cross a treacherous stretch of water called Jack Sound. When the tide is running, currents in here can reach 7 knots. The sea boils where rocks and ledges running across the sound cause sharp changes in depth. With an opposing wind, vicious standing waves form at either end of the sound.
It is dangerous enough to take a boat through it, so who would be mad enough to dive there
Thats what everyone told me, and that is exactly what I thought until some friends and I tried it. Then, wow! The current-swept rocks of Jack Sound are just covered in rich and colourful marine life.
It takes careful planning. It is not just a case of diving on slack water that is usually too short. You need to dive on the right side of the right slack water, so that when the current picks up towards the end of a dive you are not carried into rapidly growing overfalls.
North of Tusker Rock (1): Breaking the surface at the north end of Jack Sound is Tusker Rock. There are really two sites here: a plateau and wall north of the rock, and shallower ledges to the south and south-west of it.
The plateau stretches north of Tusker Rock at a depth of 20-25m for a distance of about 70m. Running round the edge of the plateau from north-east to north-west is a 10m wall.
When the tide is running northwards in Jack Sound, it splits round Tusker Rock, swirls into back eddies to the north of the rock, smoothes across the plateau, then tumbles into vicious down- and up-currents as it passes across the wall into deeper water.
The time to start a dive here is just before high-water slack, 2-21/2 hours after high water at Milford Haven. The trick is to go out in the boat two hours after high water, and kit up while watching the tumbling water and currents. As soon as the surface water flattens, but is still just flowing northwards, it is time to dive.

Descend on the north side of Tusker Rock to the plateau and follow the current and your compass out northwards. The rocky seabed is covered in jewel anemones, dead mans fingers and hydroids. As you drift across the plateau, there is a good chance of bumping into dogfish and crawfish resting on the rocks. These are enough to make any dive, but dont stop to look for too long, because you have to get to the wall before the current turns.
The wall appears suddenly. At first glance it looks plain and brown in the natural light, but shine a torch and what initially appeared to be a brown surface turns out to be a carpet of densely packed anemones (Sagartia elegans).
On corners and towards the top of the wall are clumps of white, orange and green plumose anemones. Conger eels and lobsters hide out in crevices and holes at the base of the wall. Look, but dont touch this is still part of the marine reserve.
As bottom time disappears and the current starts to turn, it is time to come back up the wall. Once you know the area well, it is possible to swim back across the plateau and ascend Tusker Rock, but until you do it is better simply to follow an SMB line up from the plateau.
No matter how good a dive you are having, this is not a safe place to build up large amounts of decompression. A safety stop is always worthwhile, but spending more than a few minutes hanging in blue water could set you off on an unplanned, high-speed drift through growing overfalls at the south end of Jack Sound!
This also brings me to why you must not attempt this site on a low-water slack. This is not a forgiving site. Below the wall you wont notice the northwards current building up above you until it is too late to surface safely. It is never a good idea to ascend into a vicious mix of strong up- and down-currents.
Until you know this site, it is essential to dive with an SMB. Once you have dived it a few times and can find your way around reliably, it is an ideal site at which to use a delayed SMB, popping it off from the plateau at the end of your dive.
South of Tusker Rock (2): As the current builds southwards following high-water slack, a wake forms to the south and south-west behind Tusker Rock. Tight in behind the rock there are gentle back eddies and it is slack enough to dive all the way through to low tide.
Before you dive, it is advisable to watch the current for a while to convince yourself it really is slack. You could even jump into the water without kit on to act as a human current monitor.
Drop in right on the south-west edge of Tusker Rock, taking care not to hit your head on it. Follow the rock down to 15-20m, then just potter about, making sure you stay within the slack area. Keep an eye on your compass and be aware of the current strength and direction at all times.
Beneath the kelp, the usual anemones and dead mans fingers cover the rock, with shrimps, squat lobsters and aggressive velvet swimming crabs filling the numerous cracks.
This is a great location for macro life. If you have dived the north of Tusker Rock and seen some nudibranchs, you wont believe the number of nudibranchs that you can see here. I have also seen the occasional octopus on this site, but the best places to find octopuses are at Wooltack Point and at the south end of Jack Sound near the wreck of the Porthgain.
Except on high-water slack, this site is just about impossible with an SMB. The buoy and line tend to drift out into the current and drag divers out of the slack area. At the end of the dive it is best to navigate up the rock to 6m, make a few minutes safety stop on the rocks, then pop up a delayed SMB for a relatively brisk ascent before you get caught in the current.
The Pit (3): While most of St Brides Bay has a silt and sand bottom, the fierce currents of Jack Sound have scoured the seabed to the north-west of Tusker Rock clear of anything smaller than a medium-sized boulder. The chart says 43m, but I have bottomed out at just over 50m on this dive.
You can do this only as a drift with an SMB. You need very calm surface conditions and a northward current in Jack Sound, but not so strong as to cause turbulent overfalls. The ideal time to start is about 20 minutes before the time that you would normally dive the plateau to the north of Tusker Rock. There will still be some turbulence to the north of the plateau, but the water above the Pit will be calm.
Start on Tusker Rock and swim west into Jack Sound. The current will pull you northwards over spurs of rock that extend downwards into the scour pit. As you drift northwards and deeper, the spurs and gullies give way to a moonscape of boulders. Here the marine life is small and close to the rocks. In some places, the rocks are scoured smooth, but in good light and visibility the dive is spectacular.
The disadvantage of this dive is that you have no choice but to ascend your SMB line from the bottom of the Pit. You need to plan for enough air to decompress on the line at the whim of the current, but not for so long that the tide changes and you end up travelling south through Jack Sound.
While you are diving, your boat cover can keep a lookout for the harbour porpoises that feed and play in this area.
Wooltack Point (4): On the mainland side of Jack Sound is Wooltack Point. This is a larger area with a wide diversity of marine life and scenery. Anemones and sea fans cover the walls and rocks. There are writhing carpets of brittle stars, as well as patches with the occasional cup coral and dead mans finger. Once again, a torch is useful because most of the rock faces are directed northwards.
The time to dive this site is the opposite of the time to dive to the south of Tusker Rock. Low-water slack is suitable for less experienced divers, while the more experienced can enjoy a slack area with some back eddies at any time that Jack Sound is running northwards.
Drop in on to the shallow rocks right under the cliffs, then swim out northwards over the kelp. At low tide watch out for rocks that could foul your boats propeller.
The topography here can be misleading. The bottom descends in steps separated by sand and mud slopes. Just follow the slope down between the steps to your planned dive depth, follow the rocks along for a bit, then meander back in over the shallower steps. End up doing a safety stop while pottering about under the cliff.
Another option is to follow a flat sand and gravel seabed west from Wooltack Point towards Tusker Rock at a depth of about 15m (but not so far out as to get caught in the current). The seabed is not particularly spectacular, but it is a great place for finding octopuses.
On one dive I disturbed a lesser octopus in a sort of Mexican stand-off with a spider crab. The octopus had intended to make a meal of the crab, but the crab had imprisoned it in a cage of legs. My arrival spurred a hasty retreat by both parties.
If you are diving Wooltack Point while Jack Sound is running northwards, you must stay aware of the current and watch your compass. Navigation by the direction of the current can be deceptive and you do not want to surface into the strong currents at the north end of Jack Sound.
The seabed around Wooltack Point is littered with discarded fishing tackle. A good deed is to take a carrier bag and pick up any litter during your dive. If you are using Martins Haven, you can hand the recovered material in at the Marine Reserve Office.
Wooltack Tunnel (5): When your dive is over, an interesting diversion is to explore the tunnel that runs through Wooltack Point from Wooltack Bay to just north of Jeffreys Haven.
It is possible to swim and scramble through the tunnel at most states of the tide. Some people even take a sea canoe through it. All you need to explore it are fins and a dive light. A RIB or inflatable boat can manoeuvre in close and drop you off at one end, then drive round Wooltack Point to pick you up at the other end.
The Cable (6): At the south end of Jack Sound is the Cable, a ledge that just breaks the surface at low tide. The Cable is normally detectable only by the fierce wake of overfalls and huge standing waves it raises when the current is running southwards into a south-west ground-swell. This is the rock on which the Lucy was originally stranded. The wreck is now located more than a mile away on the north side of Skomer Island.
Extending about a mile south of the Cable are ledges covered in soft corals and anemones. It is easy to imagine the shape of the seabed by looking at the bedding planes of rock in the nearby cliffs. The cracks in the ledges are full of crabs and squat lobsters, and ballan wrasse flit about. Its a sort of horizontal version of a good wall dive.
To dive here, you need favourable surface conditions a calm day with no ground swell. It is never slack enough to dive without an SMB, but what slack there is occurs 21/2 hours after both high and low water in Milford Haven. If you dive at low-water slack, make sure you surface before it starts running northwards.
Close in to the Cable, the ledges are covered in kelp, so a good place to start this dive is in a depth of 18-20m to the south-west of the Cable. When the current is running southwards, this area can also be good for a drift dive, as long as you start down-current from the overfalls.
The Molesey (7): Tucked in against Midland Isle, just south of the Crabstones, lies the wreck of the Molesey, a 3800 ton steamer wrecked in 1929. Today, the well-broken remains of the Molesey lie in 6-12m. Fierce currents keep most of the plates clear of kelp, making this an interesting shallow wreck at slack water. I know of two divers who have found small portholes lying on the seabed near the Molesey.
To find the Molesey, locate a vertical slit cave in the side of Midland Isle just south of the Crabstones. Enter the water about 10m south of the cave and swim out perpendicular to the shoreline. This should lead to the boilers at a depth of 10m.
From the boat, seals can often be seen in the entrance to the cave and along the shore, but you are unlikely to see them underwater.
The Molesey is diveable at 21/2 hours after both high and low water at Milford Haven, but the high-water slack allows a longer dive due to the shelter provided by the Crabstones.
The Porthgain (8): At the south end of Jack Sound in 12m of water, somewhere between 50m and 100m north of the Cable, lies the remains of a small steel barque, possibly the Porthgain. The wreck is flattened against the seabed with a few girders and winches standing proud of the bottom. Like the Molesey, it is kept clear of kelp by the strong currents.


Divernet

FACTFILE

GETTING THERE: Follow the M4 and A40 to Haverfordwest, then B4327 to Dale and Martins Haven or B4341 to Broad Haven.
DIVING & AIR: Contact: West Wales Divers 01437 781457; Nemos 01646 602030; Pembrokeshire Dive Charters 01437 781569. Take care not to disturb the wildlife, either on the surface or under water. Edible crabs, crawfish and lobsters must not be taken.
LAUNCHING: Beach-launching at Broad Haven and small boats at Martins Haven. The closest slip is at Dale.
ACCOMMODATION: Contact tourist information on 01437 763110.
FOR NON-DIVERS: Sandy beaches and coastal walks, or take a day-trip to Skomer Island from Martins Haven on the Dale Princess.Who will enjoy the diving: Anyone who is not bothered by a bit of current. Most dives need to be led by experienced divers. Careful planning and detailed briefings essential.
FURTHER INFORMATION: Admiralty chart 1482, Plans in the South and West of Dyfed, includes a 1:12500 scale plan of Jack Sound. Ordnance Survey map 157, St Davids and Haverfordwest Area. Shipwrecks Around Wales Volume 1, by Tom Bennett. Divers handout from the Marine Reserve Office at Martins Haven gives essential information on slack water and rules of the marine reserve. A display by the Marine Reserve Office at Martins Haven provides good background on local marine life.
PROS: Some challenging diving with superb marine life. Uncrowded dive sites.
CONS: Strong currents. Visibility is rarely good, but it is usually better in Jack Sound than on the north side of Skomer Island.


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