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As we neared the site, I popped into the wheelhouse and watched the echo sounder as the boat slowed on our approach to the site. On the first pass, the familiar multi-coloured silhouette of a wreck far below, rising a good 5–10 metres off the seabed, appeared on the sounder. We were in business – and the crew readied the shotline, a weighted line with a large buoy at its other end.

The UK has semi-diurnal tides, which means that the seawater flows in one direction, say south, for roughly six hours, before turning to move in the opposite direction, north, for another six hours. The current gets progressively stronger from the beginning of the six-hour period until midway through the cycle, after which the strength of the current begins to drop away and lessen towards the point when the tide begins to turn, at which point the water goes slack; there is little or no tidal flow.

The actual strength of the tide at any one time in the cycle depends on celestial mechanics and the alignment of the sun, earth and moon. There are two types of tides - the stronger are called spring tides, whilst the weaker are called neap tides.