The use of radar for preventing collisions at sea seems to have raised four main problems in applying the International Regulations for Preventing Collisions at Sea. These are: (I) In what, if any, measure radar contact covers ‘sighting’ within the meaning of Article 28; (2) whether the position of another vessel can be ascertained by radar in the precise sense intended in para. 2 of Article 16; (3) how, if at all, the use of radar should be considered to modify the ‘existing circumstances and conditions’ which, under Article 16, govern the use of moderate speed in poor visibility; (4) the application of the Steering Rules (Articles 17–27) when radar is in use.