Beware of the surge

Harbours locked in by an automatic tide gate over a sill are often subject to a surprising amount of surge for the first quarter-hour or so after the flap opens. This is especially noticeable in North Brittany, where spring tides may be rising at 10 feet per hour on ‘hours three and four’. Since ‘low water plus four’ is typically when the door flips up, the tide can literally pour in through the gap until levels equalise. Many a normally well-handled yacht has found herself driven beam-on into the neighbour’s davits as her skipper tries to steal a march by nipping out as soon as he sees the green light.