Ships are my passion. Not just any ships, you understand, but old ones, the older the better. So, unlike many academics, I have no trouble deciding which of my many conference invitations to accept. For me it's simple: is there a historic ship to be spotted in the vicinity of the conference?

Not so long ago, I accepted an invitation to make a presentation at a conference in Dundee rather than a parallel event in Florence solely on the grounds that Dundee is home to a number of historic vessels that I'd not yet seen. These include the research ship RRS Discovery, which Captain Robert Scott took on his Antarctic expedition in 1901; the HM Frigate Unicorn, built for the Royal Navy at Chatham dockyard and launched in 1824, but never put to sea; and the North Carr, the last remaining Scottish lightship.

An invitation some years ago to present a lecture annually at the University of Portsmouth was particularly welcome, since this provided me with the opportunity to visit, successively: Nelson's flagship HMS Victory; Henry VIII's ship the Mary Rose (launched in 1511 and sunk accidentally in 1545); HMS Warrior (the Royal Navy's first iron-clad warship, launched in 1860); the HMCC Vigilant (a customs cutter launched in 2003); and M33 (a Navy vessel built in 1915, which later became a minelaying training ship renamed HMS Minerva).

An invitation to a seminar in Newcastle upon Tyne facilitated a visit to see Blossom, a longshore fishing boat dating back to 1887, and Glad Tidings, a fishing coble built in 1929. A meeting in Edinburgh allowed time for a tour of the Royal Yacht Britannia at Leith. A conference in Liverpool enabled visits to the Edith May, a Thames spritsail barge built in 1906, and the Edmund Gardner, a 1953 pilot cutter now sitting in the Albert Dock. I could go on...

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I've been ship-spotting for so long now that I can hardly remember the first one I went looking for. But like most deep passions, this one started young. As a small boy growing up in the North Wirral in the 1950s, I could look out of my bedroom window and see a long line of vessels waiting in Liverpool Bay for a berth in the docks to become free. At that time, the docks of Liverpool, Birkenhead and Wallasey were hives of activity, with a steady stream of Royal Navy vessels also making an appearance. I can still hear the haunting sound of the foghorns around the Mersey.

When I was 10, my brother and I were taken by our parents on the ferry across the Mersey to the Prince's Landing Stage in Liverpool, where the Royal Navy aircraft carrier HMS Ocean was making a courtesy visit. The queues were enormous, and after waiting for several hours we were eventually told that no further visitors could be admitted. On getting home, my mother, who was not known for her restraint when she felt a complaint was called for, immediately put pen to paper and deposited her letter to the ship in the post.

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The next day, a reply from the admiral himself was delivered by hand, telling us that he was most sorry that we had missed the opportunity to visit his flagship (I still have the letter). We were invited for a tour of the ship before it set sail that afternoon and the admiral sent his car to pick us up. We were piped on board, favoured with an audience with the admiral himself, and given a personal tour of the ship.

There were other early influences. My mother was a Geordie and her brother, my uncle, was a senior trade union official at the Swan Hunter shipyard at Wallsend. Our twice-yearly trips to Tyneside to visit our grandparents always seemed to coincide with the launch of one ship or another, and we invariably managed to get a grandstand view from within the dockyard.

Such experiences stay with us, and my enthusiasm for ships continued unabated. At secondary school we had a Ships Society, which offered visits to ships, talks about ships and films about ships. At lunchtime it was just a short walk from Wallasey Grammar School along Manor Lane to the riverside at Egremont. Here we could watch countless ships coming and going, including the big Empress liners at the start or end of their journeys across the Atlantic. And the comings and goings on the Mersey were reported nightly in the Liverpool Echo.

My familiarity with useful books on the subject grew in 1962 when I won a school essay prize. I spent most of the money on a textbook on anatomy, physiology and hygiene (rarely opened since), but I had 3/6 left over. This I spent on a little book by H.M. Le Fleming, with the glorious title Ships of the Mersey and Manchester (1959) - and it is still a treasured possession. On its inside covers, in full colour, were the funnel markings of 96 companies that sailed their ships into Liverpool. Within a short time I had memorised them all.

By the time I returned to Merseyside in 1974 to work at Alder Hey Children's Hospital, the opportunities for ship-spotting were much diminished. But the chance to visit ships in other parts of the country came to me more by accident than design. I received a small research grant to visit other children's hospitals in Britain to gather information about children's medicines. I soon realised that many of these hospitals were in port towns and cities, so off I went to Bristol, Glasgow, Edinburgh and London to collect information - and to visit ships.

A whole new world of ship-spotting opened up as I was driving home from work at St George's Hospital in London one day in 1985. I was listening to a Radio 2 broadcast in which the presenter John Dunn interviewed maritime historian Norman Brouwer, who was talking about his latest book, the International Register of Historic Ships. Of course, I promptly rushed out and bought a copy. It was to have a profound impact on my travel arrangements for years to come.

I remembered my Alder Hey experience and realised that travel awards and scholarships provided an excellent opportunity to get to certain places that might not otherwise be accessible. One of my first successes was a North American trip. A fellowship in 1985, ostensibly to study clinical pharmacy performance indicators, facilitated a trip to the US, where ships waiting to be seen included the Lightship Ambrose and the iron sailing vessel Wavertree in New York, the Philadelphia in Washington, and the SS Clipper and the Marquette in Chicago.

A year later, in 1986, an ICI travelling fellowship facilitated a trip to Australia. This time the pretence was the study of workload-measurement systems, but in reality it was an excuse to visit a number of the historic vessels resting in Australian waters. These included several in the collection of the Australian National Maritime Museum in Sydney, and the replica of HMS Buffalo, the vessel that brought the first free settlers to South Australia in 1836, now moored at Glenelg near Adelaide.

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There was also my Council of Europe medical fellowship in 1991. This was nominally awarded to allow me to carry out a study of performance measures in Sweden compared with the UK. It was of course a carefully disguised excuse to visit one of the most important historic vessels in Europe, the Vasa. This was the first ship with two gun decks, built in the Royal Naval Shipyard in Stockholm. Unfortunately, it was too tall and too narrow, and sank off Beckholmen on its maiden voyage in 1628. It survived almost intact and was raised to the surface in 1961; it is now preserved at the Vasa Museum.

I've been back to Sweden several times for conferences and meetings, not least because Stockholm also boasts many other historic vessels. A walk around the island of Skeppsholmen is a must for the avid ship-spotter, since it is home to dozens of vessels, some of which can be visited. The largest of these, the af Chapman - originally a full-rigged cargo ship, and built in Whitehaven in 1888 - is now a hostel. And some of the historic steamships are still carrying passengers between the islands today.

The dedicated ship-spotter does much more than simply spot ships. He (and yes, it is usually a "he") often goes to great lengths to obtain a photographic record of the event. In fact, Ships Monthly includes a regular page for ship-spotters, telling them not only where to catch particular ships but also the locations from which to take the best photographs. There are a number of online communities for sharing ship photos and related images. Some of them now contain nearly one million pictures of vessels old and new, with images added at the rate of nearly 500 a day.

The fascination of old ships is the insight they offer into human ingenuity; how solutions were found to seemingly impossible problems, such as building wooden ships longer than the tallest tree. The history of ships is the history of mankind, of science and technology, of conflict and exploration. It is impossible not to wonder at the courage of those who sailed in these vessels, the hardships they endured, the adventures they experienced, and the lands and sights they encountered for the first time.

These ships' present-day locations, almost always by the sea, are of course an added bonus. In reality, ship-spotting is inextricably linked to the smell of salt air, rotting seaweed, freshly caught fish and the sound of squawking, circling seagulls.

Without these accompaniments, the ship-spotter feels distinctly cheated.

New ships are constantly being added to the registers of historic vessels worldwide, and one of the joys of ship-spotting is that you can never quite be sure which ones you are going to come across in a particular place. Sometimes historic ships look unpromising from the outside but are a source of great delight once inside. Some have become museum ships, while others are still in service, such as the paddle steamers that still ply their trade up and down the Mississippi River, or those that have been reinvented as hotels or conference venues, such as the RMS Queen Mary at Long Beach, California.

So are there any places left on my list of desirable conference venues where historic ships can be spotted? It's funny you should ask: there are quite a few. The MV Yavari was a passenger and cargo vessel commissioned by the Peruvian government in 1861. It was prefabricated at the James Watt and Company foundry in Birmingham and delivered in small pieces by mule to Lake Titicaca, two miles above sea level, where it was reassembled. Today it is berthed at the town of Puno on the shore of the lake.

And then there is The County of Roxburgh, a magnificent four-masted, full-rigged ship, built in 1886 by Barclay, Curle and Company in Glasgow. It currently lies beached on the Takaroa Atoll in the Tuamotu Islands in the South Pacific.

Now where did I put that list of forthcoming conferences?

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