IT'S AS MUCH A ROUTINE AS GOING TO THE OFFICE, and I've been doing it every summer for 10 years.
We sit on the rocks while my tender (son Peter) helps me into the harness which takes the strain off the air hoses, humps an 18kg DUI weight system over my shoulders, and adjusts the surface demand system which we have rigged to a Buddy Commando BC incorporating a 3 litre bail-out.
Beside me, fellow-underwater archaeologist Graham Scott kits up too, assisted by his tender Brian Hession. Dive supervisor Jane Griffiths, who runs her own diving business and hunts scallops when things are slack, runs through the checks.
Now it's time to start the hookah compressor and don the Interspiro masks before roping backwards down the rock face and into the water. As I sink through the kelp, Jane's voice comes reassuringly through the Buddyphone earpiece: "Surface to Diver 1 - comms check - over."
Communication established between divers and surface, Graham and I descend to our workplace on the seabed at the base of the cliff, which slopes down from Duart Point on the Isle of Mull. I've been coming here every year since 1992 to work on the historic shipwreck discovered by naval diver John Dadd in 1979. It was rediscovered in a state of disarray by the Dumfries and Galloway branch of the Scottish Sub-Aqua Club (DAGSAC)13 years later.
Fast currents and seabed erosion had uncovered and were rapidly destroying fragile organic remains, the like of which had not been seen since the excavation of the Mary Rose.
Led by the Archaeological Diving Unit (ADU), the DAGSAC divers helped to recover the exposed objects, which were then rushed to the National Museum of Scotland's conservation laboratories in Edinburgh for emergency treatment. Under- water archaeology's shock troops had won the first round.
The finds showed that the wreck had occurred around the middle of the 17th century. Archival detective work by Donald MacKinnon of DAGSAC revealed that it had been part of a small task force sent by Oliver Cromwell in 1653 to sack Duart Castle, stronghold of the Maclean clan, whose chief supported the exiled Charles II. But when they arrived the Macleans had fled.
At this point a storm struck the fleet, sinking two merchant ships and a small warship called the Swan. It was clear that the wreck off Duart Point was one of these vessels - but which one?
Carvings from the ship's stern provided the answer. Over the years, several pieces have been found scattered around the site - a puffy-cheeked cherub, a classical warrior and a draped female figure with an anchor at her feet. These are all reminiscent of the elaborate ostentation which Charles I - who built the Swan in 1641 - liked to adorn his ships.
The clinching evidence was a fine example of the coronet, ostrich feathers, and "Ich Dien" badge of the Prince of Wales. This wreck was clearly no lowly merchant vessel, but a prestigious warship that once belonged to an English king. It can only have been the Swan.
With help from the ADU and DAGSAC the wreck was monitored over the winter of 1992-3, and freshly exposed areas protected in the short term by sandbags (see Diver, February 1996).
But a long-term solution required a more sustained programme of monitoring and, if necessary, the careful excavation of the most threatened parts. This needed a qualified archaeological team, time, and quite a lot of money.
Up to this point I had been no more than a willing surface-bound helper. My diving days had ended (or so I thought) seven years earlier, when excavation of the Armada wreck La Trinidad Valencera off Donegal, carried out with the City of Derry Sub-Aqua Club, had been completed.
In the meantime I had become a middle-aged academic, with out-of-doors research confined to archaeological aerial photography - an undemanding pursuit conducted from a comfortable seat detached from the world below, recording ancient landscapes at the click of a button. Much easier than diving, and therefore more congenial - or so I thought.
Martin Dean of the ADU persuaded me otherwise. Somebody had to take on the project for the long term, and ideally it should be an archaeologist who dived. Why not me? I suspect he couldn't think of anyone else.
But there was a catch. In the good old days I had managed well enough on the basis of questionable qualifications but long diving experience. This was no longer good enough. By the early Ô90s Health & Safety requirements for diving at work demanded a proper commercial ticket, and I could get this only by passing a full HSE assessment.
No problem, I thought - my old buddy Alan Bax at Fort Bovisand would surely put a geriatric colleague through with a nod and a wink. Did he hell! Assigning me to a class in which the next oldest member was less than half my age, and with instructors who had learnt their trade in the Royal Marines and weren't going to let anyone forget it, we were chased everywhere at the double (above and below the water) and expected to respond unquestioningly to barked words of command.
In mid-jump from the 6m Bovisand breakwater, I remember wondering whether it was all worth it.
It was. HSE diving is very different from the kind of sport-oriented diving with which I had been familiar, but it is geared towards conducting underwater work safely and efficiently. It has worked brilliantly for us at Duart. With our fixed shore location, surface supply and unvarying routines, we can concentrate on the archaeology, focusing our attention on the careful and tricky business of survey and excavation in dive stints which often exceed two hours.
Because it's such a small and tightly contained site, there is space for only two divers to work comfortably. During the initial part of the project, when survey was the main task, we worked with two pairs, swapping jobs in morning and afternoon dive sessions.
Excavation involves much more post-dive work - drawing and photographing finds, updating records, and providing first-aid conservation and storage for often very fragile objects, so a single daily dive is all we can fit in.
Our support staff on the dives become archaeological specialists afterwards - sons Peter and Edward help with the drawing and photography, while Dr Paula Martin (also my wife, and a one-time archaeological diver herself) combines the posts of deputy director and finds manager.
Slowly, over the years, the Swan is coming back to life. A substantial part of the ship's bottom has survived, pinned down by the stone ballast which had been placed forward and aft in the hold. We have excavated the saddle between these mounds to reveal frames and planking, including parts of the mast step and pump well.
Beyond the ballast we have uncovered part of the much-eroded bow structure, and have tentatively identified the stern skeg, giving an overall length along the keel of about 66ft.
The maximum beam, revealed by framing up to the turn of the bilge, is around 22ft, giving a length/breadth ratio of 3:1, characteristic of the sleek build of a light warship.
In the bilges we have found deposits of a glutinous and foul-smelling sludge - muck to some perhaps, but to the environmental scientists who will examine it, a fascinating source of information about diet and hygiene on board.
Quantities of butchered animal bones - mainly cattle and pig - will throw further light on contemporary diet, while a number of human bones have also been found. They were disarticulated and scattered widely around the stern area of the ship, but almost certainly belong to the same individual.
About 60% of the skeleton has been recovered, enough to allow forensic anthropologist Dr Sue Black to build up a remarkable profile of this shipwreck victim.
He was a young man of between 23 and 25, who in his childhood had suffered from rickets, which left him, at around 5ft 3in, several inches shorter than he might otherwise have been. But while his lower body was bow-legged and rather puny, above the waist he was built like King Kong.
His shoulder, arm and wrist muscles were exceptionally well-developed on both sides (unlike a modern tennis player, whose serving arm is normally much the stronger), suggesting constant and heavy activities such as pulling and hauling.
Our sailor also had a repetitive strain injury to his upper thigh joints consistent, thinks Dr Black, with regular jumping from a height of 2m or so.
A seaman with square-rigger experience recently told me that it is normal practice to jump that distance to the deck after coming down the ratlines, to avoid an awkward scramble over the bulwark and the possibility of falling overboard.
This Cromwellian seaman was evidently fit, healthy, and well fed, although if he had survived he would have had problems in store. His molars were ground almost flat by grit from the stone-ground flour which made up a major part of his diet; a few more years and they would have worn down to the nerves, with consequent agony. He also had a congenital spinal abnormality which would increasingly have disabled him in later life.
The question of human remains on wrecks is a sensitive one, and we regard the Swan as much as a war grave as more recent military wrecks on which life has been lost.
When the scientific investigation of our seaman is complete, his bones will be laid to rest, in memory of himself and his comrades who died so far from home three and a half centuries ago.
Other finds from the wreck have fleshed out the skeletons of the ship and its dead crew-member. Much relates to the running of the vessel and the specialised tasks of those on board: part of the binnacle and two mariners' compasses; navigational dividers; blocks, rope, and barrels; bits of wooden lanterns; and weights stamped with the official mark of Charles I.
Various pieces of weaponry have been found: part of a snaphaunce pistol, musket bullets and powder flasks, and two concreted swords. Eight cast-iron guns are scattered over the wreck site: most have been left in place because of the difficulty of conserving them, and to make the wreck an interesting dive for visiting divers.
One small gun has, however, been raised because it was found complete with its carriage and port cover: together these items will allow us to piece together much new information about contemporary shipboard gunnery.
Utensils and personal possessions are poignant and revealing reminders of those who owned and used them. We have found turned wooden bowls and staved mugs, pewter plates and flagons, clay pipes and pottery. Some of the pipes are stamped with the initials NW, apparently those of a Newcastle pipemaker who supplied Cromwell's forces in Scotland.
Three Bellarmine stoneware flagons, with their grotesque facemask decoration, have turned up on the wreck. One is still stoppered, and its contents are intact. They have yet to be analysed. Well-preserved ointment fills a small drug pot, the fingermarks of its last user still crisp in its surface.
The biggest surprise, apart from the carvings, was the lavish nature of the captain's quarters. Much of the stern appears to have collapsed inwards, and many of the finely fashioned interior fittings have been preserved. A small warship of this class was supposed to be free of interior panelling, for it added extra weight and made the hull less flexible, but the Swan was elaborately provided with moulded frames and panels, including an elegant door.
Along with the carvings, these finds confirm that Charles I believed it was more important for his ships to project kingly power and prestige than to maximise fighting efficiency.
Two more diving seasons are needed to complete work on the Swan. By then all the threatened areas will have been excavated, and their contents conserved for eventual display by the National Museum of Scotland. What remains will be secured for future generations and regularly monitored.
Archaeological reports and popular accounts will be made available for specialists and the general public. A television documentary has been shown in the BBC2 series Journeys to the Bottom of the Sea, and others are in the pipeline.
I'll be 65 by the time the project is finished, but I hope the Swan won't be my swan song. Having got a second diving wind, I see no reason to stop again, and there's a fabulous site in a Scottish loch I'm just itching to get my hands on!
The Swan site is a protected historic shipwreck in the care of Historic Scotland, and unauthorised diving on it is prohibited. However, a visitor scheme has been operating since 1995 for both the Swan and nearby Dartmouth sites. Details from Philip Robertson at Lochaline Dive Centre, 01967 421627, www.lochalinedivecentre.co.uk.
John Dadd (left), who discovered the wreck in 1979, hands a bronze cauldron to Colin Martin, to be deposited in the National Museum of Scotland
Archaeology under water is the same as archaeology on land - only wetter.
Colin and Paula Martin examine a recent carving recovered from the Swan
Forensic anthropologist Dr Sue Black examines the remains of one of the wreck's victims.
Three Bellarmine pots from the Swan. Two have their corks still in place
Excavation of the Swan's collapsed stern reveals an intact cabin door.
Colin Martin and archaeologist Graham Scott discuss the day's task, with Duart Castle in the background