To avoid a danger when a wave height of a prescribed value or more starts to generate by outputting a notification signal to a notification machine when a measured value or an arithmetic value from at least of either one of a distortion measuring device and an arithmetic part exceeds a prescribed value.
Distortion amount of a hull 5 is detected by a distortion measuring device, and a prescribed position 7 of the hull 5 and a first distance up to a top of a wave are measured by a measuring part. By arranging an accelerometer at the prescribed position 7 of the hull 5, detecting acceleration when the hull 5 moves in the vertical direction by the accelerometer, integrating acceleration according to oscillation of the prescribed position 7 from the accelerometer in an arithmetic part and calculating moving amount in the vertical direction of the whole of the hull 5, a second distance Z is determined. By subtracting the first distance 5 from the second distance Z, a wave height (h) from a still water level 9 is calculated. When a measured value or an arithmetic value from at least either one of the distortion measuring device and the arithmetic part exceeds a prescribed value, a notification signal is outputted to a notification machine. As a result, quantitative monitoring can be performed and a dangerous state is surely and quickly avoided even during the night and a safety voyage can be performed.
MIZUNO SHIGEYA
ISHIHARA TERUHISA
HIDA HITOSHI
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