Validation of Radar Simulator Results by Comparison with Observations of Overtaking Manœuvres at Sea

Abstract

in the January issue of the Journal (34, £3), described an optical aid to the speed control of ships approaching their berths. There is repeated reference to the device measuring the speed of the ship. In fact, it measures bearing from the light source, which, if the ship's track is well defined, can be converted into position. It is position error that their ingenious display system gives to the master or pilot. If, however, he applies an acceleration to the vessel in an attempt to keep it at the planned position, the effect will be a pendulum-like oscillation in speed. (To correct a position error the vessel must travel at the wrong speed and after the error is corrected the wrong speed will produce a new position error with the opposite sign.)To hold the desired speed, the vessel should be controlled to hold the position error constant, not to correct it. There is now the difficulty that the accumulation of speed errors may cause the vessel to drift out of the useful cover of the traverse light, and it would then be necessary to select a new and more appropriate traverse.I NOTE with interest the paper by Dr Curtis and Mr Barratt in this issue of the Journal concerning validation of radar simulator results. At Plymouth we are constructing a computer model of ship behaviour 1 , the initial values in the model being extracted from data amassed from questionnaires. These questionnaires were given to practising navigators studying for Department of Trade examinations, one question being 'In fog you are overtaking a vessel steaming 4 knots slower than your own on a parallel course. What is the minimum track separation at which you would pass without altering course?' A range of answers was provided between 3 cables and 2 miles. By extracting the results of those respondees who were serving on board 16-knot vessels (as used in the simulator experiments) the following 'probability acceptance' graph is drawn for comparison.The minimum safe overtaking distance (MSOD) given by Dr Curtis for this situation is 8£ cables 2 ; nearly all questionnaire respondees said they would