A container vessel and sailing yacht collided while under way in heavy fog. The master had been on the bridge since sailing (a period of 15 hours). Why did it happen? 1. The container ship was proceeding at 25 knots in heavy fog conditions. 2. Her master was over confident in the accuracy of the ARPA and willingly accepted a too small passing distance. 3. The skipper of the sailing yacht was unable to use the radar effectively. 4. Both vessels did not keep an effective radar look out. What can we learn? When navigating in restricted visibility, it is important to assume a safe speed and to maintain a proper radar and visual look-out. Judgement can be affected by prolonged hours on duty.