WHAT TO EXPECT...

STRONG CURRENTS

When currents hit a headland, they are deflected down its side and accelerated, as shown to the west (left) of Portland Race on the Tidal Compass opposite. In many ways a similar effect happens with the wind, and it has been noted that winds are especially fickle around headlands, ranging from calm to severe as you pass around.

OVERFALLS

When tidal currents are funnelled down a headland they often crash into an underwater extension of the headland. On a calm day, this will create a roaring cacophony of breaking waves, while the surrounding waters are completely flat. This often gives a false sense of security to the unprepared, and the transition from calm to chaos happens shockingly quickly. The best way to avoid these overfalls is to stay well away from the headland, or time your passage for Slack Water. Because the conditions are powered by currents, if there are no currents there will be no overfalls and you will have a window of opportunity to pass through safely – especially if it is Neap Tides just after a half moon when Slack Water lasts longer and the currents are not so fast.

EDDIES

Eddies are areas of water where the currents flow in a circular direction and they are often found on the ‘downstream’ side of a headland (see Tidal Compass opposite). The theory goes that a fast current will hit the headland and flow around it, leaving an area of low pressure immediately downstream. Nature’s response is an eddy circulating water against the prevailing current to ‘fill the gap’ of low pressure. The edge of the eddy, where the two currents collide, is called the eddyline and it’s where whirlpools are of often found, their size determined by speed of currents.