A little way up the River Tamar, past the wide and busy Hamoaze, where warships are moored in the dockyards and the big chain ferries clank across between Devonport and Torpoint, and just before Brunel’s railway bridge, is the confluence with the St Germans, or River Lynher. This is a wide expanse of water with extensive mudflats and tidal lakes. On the north side the Great Western Railway marches westward across inlets and tributaries on the stone arches of Victorian viaducts. The channel up the river is narrow and shallow, so I have to wait till past half tide, when there is enough water for Coral’s deep keel.

After about two miles, the river quite suddenly narrows and the banks steepen as it sweeps round a big curve. On the outside of the bend, just where a cluster of dark pine trees grow high at the top of the bank and alongside a patch of light coloured rock on the foreshore, there is a small area where the water deepens to twenty five or thirty feet at high tide. This is the Dandy Hole, where even a deep-keeled yacht can remain afloat as the tide drops away. It’s a suddenly quiet place, away from the bustle of the main river.

The south shore is steep and tree lined, mainly stunted oak, but some pine and alder. The lowest branches hang over the river, cut off abruptly in a horizontal line about a metre above high water. Today the trees are blown around by the fresh breeze, their spring fresh leaves dancing in a pattern of pastel greens. In contrast, on the north bank a hill rises in a gentle slope, open fields planted with a uniform green cereal crop, criss-crossed with lines where a tractor has systematically passed. Just above the shingle beach at the water’s edge stand a row of hawthorn trees in the full white of May blossom.

It is high tide, springs. The river is full to the brim. The afternoon’s fresh westerly wind has died back and veered northerly. The stream no longer pulls Coral against her anchor chain, for the flood has finished. The sun too is setting, the long shadows cast by trees and hedges are deepening, and only the high points on the undulating fields catch the light. There is a twittering of birds in the trees, from time to time the caw of a crow. And was that an owl I heard call?

The evening sun hangs low and, as the Earth rolls round, finally drops behind the trees up the river. Above where it set, the fattened crescent of the waxing moon, three days past new, appears in the darkening sky, Venus shining next to it. ‘Of course,’ I say to myself, ‘spring tides, and sun and the moon are on the same side of the earth pulling the water together.’ I have known this in theory for many years, but never before seen it so directly.

Everything is poised, as if waiting for the next move in the rhythm of days and nights, ebb and flow, wind and calm. Coral, too, is waiting, swinging quietly this way then that between wind and the remaining tide. And then, ever so gently, water begins to flow downstream. The pressure on her keel becomes more powerful than the force of the light breeze, and she begins to swing. For just a few moments she catches, broadside across the river as if holding the moment of anticipation, reluctant to commit herself; and finally firmly points her bow upstream. The ebb has begun.

And I have been sitting in the cockpit watching the turning of world for nearly an hour. Now the new phase has set in I feel released to go about my evening chores. I go below to get ready for the night.