Today on a seismic ship no one could steer as fine a course as required hour after hour to satisfy the peculiarities required , and even the automatic steering that most of us were brought up with , such today would be considered off the Ark. computers control the Automatc steering and the helmsman is just adjusting the computer to suit the weather and sea conditions , more than half a degree of deviation from the course required could result in the loss of hours of survey , which means huge monetary losses . Speed is also a big factor and is usually 4 knots over the ground this to is computer driven . JS