Oil tanker in typhoon Judy, Japan Sea 1963
The Derbyshire was lost on either 9 or 10 September 1980 in typhoon Orchid.
A typhoon is the name given to a tropical revolving storm in the China Sea and off the coasts of Japan. In other places such storms are called hurricanes or cyclones.
Typhoons are seasonal, occurring principally towards the end of the hot seasons. They have winds of force 12 or greater on the Beaufort Scale – that is upwards from 118 km/hr (73 mph).
The behaviour of typhoons is closely observed by satellite, aircraft and radar. Although the rate of movement of the centre of a typhoon is generally less than 15 knots, they are still difficult to predict because their course can be very erratic. In fact, various forecasting bodies gave different positions for typhoon Orchid.
It can be impossible for the crew to know exactly what the sea state is during a typhoon. Visibility can be severely limited by the spray blown off the massive wave crests combined with driving rain. In these conditions all the crew can do is feel the ship’s violent movement and try to keep on a heading where she will suffer the least damage.
For all these reasons, typhoons can have a devastating effect on ships.
The maximum wave height that the Derbyshire might have encountered during typhoon Orchid was 10.86 metres (36 feet). Yet reliable sources now say that freak waves up to 30 metres high (100 feet) do exist and they are not infrequent. Could the Derbyshire have encountered such a wave?
For centuries sailors have blamed rogue waves for causing mysterious sinkings, but others would not believe them. However there is now evidence that massive waves are more than just a maritime myth.
Conditions for the Derbyshire
We can only guess what the conditions were on board the Derbyshire during typhoon Orchid.
It seems that on 7 and 8 September, the days immediately before the Derbyshire was lost, the wind and sea conditions almost 250 nautical miles west-north-west of the typhoon’s centre made it unsafe for the ship to change course to the south-west to avoid the typhoon.
By 5pm on 9 September 1980 (the day that the Derbyshire sent her last ever message) some waves rose to a peak of 10.86 metres (36 feet) and the wind speed was over 56 knots.
It is estimated that, when the Derbyshire was lost, the waves were just slightly longer than the length of the ship, so her bow would have been submerged before she had the chance to rise above the waves.
A characteristic of typhoon Orchid was that its wind field caused high swell and seas were abnormally extensive. High waves they tend to have very steep fronts, which allow little time for a ship to rise above them.