Speed through water arpa The ship’s course and speed were more or less steady except for the usual variations experienced at sea in auto pilot mode. Bridge Team need to use both Speed Over Water as well as Speed Over Ground cau ously. Speed over ground should be used for navigation. Details of Training: Why speed through water is used in ARPA for collision avoidance purposes . The most accurate speed available D. A ship with her engine stopped in water with 2 knots currents will have zero speed through water but will have 2 knots speed over ground. Sep 25, 2016 ยท So in this case the vessel is making way through water. The waves that are reflected from the layers of seawater the speed shown will be speed over water. sound waves travel at a constant speed through water b. Navigator should make full use of these speeds where these best fit. dqpphz dmojv kht lph qxykfyc jfhw wsjm rsujf coolu mqxa