Certainly genuinely unavoidable aberrations in human behaviour exist. In surface navigation, however, these momentary blunders seldom lead to fatalities such as collisions or groundings, although in shiphandling they can cause collisions when coming alongside or when manoeuvring in a confined space, but usually only of a minor nature.

The examination in the R.N. Navigation School of some sixty collisions and groundings has revealed that in only two have aberrations played any significant part in the subsequent disaster. This is quite easily explained for two reasons. First of all ships at sea usually close one another or approach a danger at a comparatively low speed. Furthermore the prudent mariner reduces speed when danger exists and when the situation becomes tense. There is therefore usually time for the nature of a blunder to be recognized and for the necessary corrective action to be taken, which, if not resulting in immunity, will reduce the gravity of the incident. Sixty knots is an exceptionally high relative speed on the surface, yet this provides minutes for human reaction as opposed to seconds or even split seconds normally available in the air.