According to the Convention on the International Regulations for Preventing Coliisions at Sea，1972 ． ， is stated clearly in Rule 5 that aural look − ou 亡 shall be main 亡 ained at all t三 me ． How sha ！ l we do as a navigator keep a proper watch concerning aural look − out consider g the signa1 ？ So we practised the measurement of noise level of experimeta 工 ship and analysed them and then gained the total transmission loss and 皿 inimum audible sound pressure ． We compared dhe ． minimun ユ audible sound pressure in the op ed ・ bridge with closed − bridge． 1． NQise level Qf experimental ship ' s bridge is very high and so thresheld of audibility is high。 We need to contrive to deaden the n 。 ise of bridge． 234 Minimum audibility sound pressure level in the opened − bridge 三 s less 10-20 dB than closed もridge ． We must always keep a watch under opening windows and doGrs ， Distance of audibility on the experimental ship is extremely short ．

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This paper is ， to study navigators ' vistual acuity ， the result of investigation on cadets on training ships ． Weak sighters are obviously inferior to normal ones in looking out ， star finding etc ． It requires further examination