COASTAL DISCOVERY

This month William Thomson explores the reassuring realm of the harbour, choosing Weymouth in Dorset to anchor up his catamaran Luna, while nipping over to nearby Portland for an exciting session of wing surfing

William Thomson continues his series on geographical coastal features by examining what makes a safe harbour

When three days’ notice was given for the second lockdown last November, our catamaran Luna was snug in Weymouth Harbour, Dorset. We had a decision to make; do we take to the high seas and sail south to warmer climes, or brave the winter in our noninsulated boat, safe in harbour? If I had an experienced crew and we knew the boat’s sailing capabilities well, I would have chosen the former. But both my crew and the boat were untested; we had only started cruising in her a week beforehand and that was Naomi’s first time sailing a yacht. As for the kids, Ottilie, aged six, and Arva, four, showed great potential, but they needed a little more training before crossing the Bay of Biscay. So we decided to bide our time, brave the winter and start cruising in the spring. This gave us a decision; which harbour do we make our home for the winter – Weymouth or Portland? I got out the chart to study topography and wind patterns, coming to the conclusion that despite their reputation as places of refuge, not every harbour is perfect and they all have own unique strengths and weaknesses.

Weymouth is as close to the perfect harbour you can get, but for its one Achilles’ heel – the beast from the east. Because of its orientation, when a strong easterly wind blows, the swell crashes into the harbour wall and makes the entrance a mass of whitewater. Furthermore, add a little north to the wind and the swell rumbles all the way up into the inner harbour, yanking the ships hard on their mooring lines. Despite this discomfort, the prevailing winds in the UK are from the south-west, from which Weymouth and Portland are protected by the famous Chesil Beach and Portland Bill (which we explored in the ‘Headlands’ feature). This means that the wind can blow from the south-west up to hurricane force and Weymouth Harbour will stay as flat as a millpond. Portland is an anomaly here, because its huge size means a swell can actually generate within the harbour. This is visible even when the waters close to Chesil Beach are flat, but as the ‘fetch’ (area of water the wind blows over) increases, the swell increases in the harbour and sometimes waves even break against the harbour wall, from the inside!

So the main consideration when anticipating what to expect from a harbour is the wind direction. Putting aside the swell breaking from the inside of a harbour, most harbours will be well sheltered from cross-shore and onshore winds. But it is the onshore you want to be especially careful with.

‘The wind can blow from the south-west up to hurricane force and Weymouth Harbour will stay as flat as a millpond’

In addition to the swell surging into the harbour, when the waves hit the harbour wall they often bounce back and collide with the oncoming swell, creating ‘rogue waves’ that look like a boiling cauldron being stirred. Secondly, if the tide is ebbing then it often generates currents flowing out to sea and when these hit the incoming wind, steep breaking waves form (as we discovered in the March feature exploring ‘Channels’). Another consideration with the tide is that many harbours in the UK actually dry out at low tide, so there is no water at all for half the time. To learn if a harbour dries out, look on a nautical chart to see the numbers. If there is a line beneath a number, such as

1.5 for example, it means that the harbour dries out when the tide is below 1.5m.