The Petula Transatlantic Expedition, 1953–4

Extract

Powered research ships are the basic vessels from which the science of oceanography is conducted. For the investigation of certain surface water problems, however, a large, powered vessel is not the most suitable platform, for, while affording ample accommodation and working space, she may have fundamental faults. Her deck may be far above sea-level so that in bad weather direct observation of marine life is impossible. More important, her mere presence may alter the very characteristics, both physical and biological, which are being studied. Thus her hull, rolling, pitching and threshing in a seaway may appear to some animals as a fearsome intruder. The throbbing of her propeller sets up low-pitched vibrations powerful enough to alert the fish for miles around. The sea close to the engine room becomes warmed and to it is added hot water from the condenser. There is violent water mixing by the bow wave. These factors in combination effectively alter both the sea temperature and the thermal stratification. The ship's wash, thrown away from the sides, may set up a heavy cross sea which distorts the shape of nearby waves, particularly in regard to their steepness and height.