Human error accounts for a number of collisions at sea; nevertheless, it is widely accepted that vessels are inclined to produce widely varying ranges of radar echo strengths in real sea conditions, in contrast to their ‘true’ anechoic strength, which tends to be minimal for a small and structurally non-reflective craft; even for the calmest possible water conditions.

In this paper experimental results for small craft will be presented and analysed in an exploration of potentially influential parameters in such cases. These results are based on three series of sea trials. Furthermore, an attempt is to be made to portray the inherent, theoretical and/or practical, limitations in the radar detection of small craft in real (estuary) sea conditions.

My background is that of a professional navigator but, although I have spent a lifetime at sea, my experience as a harbour master gathering knowledge about problems in inshore waters has been limited to only the last three years. My aim is to be moderately – but deliberately – provocative in order to help stimulate discussion, though I suspect, with the strongly held views on the subject, this may not be necessary. I do not suppose there is anything new in what I am going to say and far greater minds than mine have been hard at work for many years in seeking solutions to some of the problems I will outline. Given all the diverse interests in this subject, there will perhaps never be a perfect answer but one of the important things is that the dialogue is ongoing, and embraces many organizations and authorities. This paper reflects the problems we perceive in the area of the Solent and, although some issues can be read across in general terms for other areas in the UK, the Solent is a unique area with perhaps unique problems. So what better place to start-Before I outline the scope of the problem, I must stress that the views I expound in this paper are my personal views, and should not in any way be considered official MOD policy. I would also like to say (and some readers may take issue with this by the end) that I believe my views are impartial – my main task as Queen's Harbour Master is to protect the interests of the Ministry of Defence and, once that duty is fulfilled, I have no commercial or financial axe to grind. When I look at some of the maritime safety problems, I can do so free from hindrance or pressure.

Criteria and a methodology for evaluating the relative effectiveness of different navigation aids in a coastal region, taking account of the ship-borne equipment, human factors and the needs of the navigator, have been discussed in the Nautical Institute' recently-published book on Pilotage and Shiphandling. The method is based on the product of the probabilities that the equipment will be fitted, that it will be available (in reliability terms), that it will be properly used and that it will provide the required information.