Stability indicator for marine vessel
First Claim
1. A stability indicator for a marine vessel, comprising:
- sensor means for producing a first signal having a continuously variable characteristic, such as voltage magnitude, that continuously varies in a predetermined manner as the roll angle of the vessel continuously varies, such that the instantaneous value of the roll angle may be determined by measuring the instantaneous value of said characteristic; and
processing means including means for receiving said first signal and for repeatedly measuring said characteristic over a period of time to thereby determine a plurality of instantaneous roll angle values over the period of time, means for determining the vessel'"'"'s rolling period based on said plurality of roll angle values, and means for determining a GM value equal to the square of the vessel'"'"'s beam length times the square of the vessel'"'"'s rolling constant divided by the square of the vessel'"'"'s rolling period.
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Accused Products
Abstract
A stability indicator for a marine vessel. The indicator continuously determines a GM value for the vessel equal to the square of the vessel'"'"'s beam length times the square of the vessel'"'"'s rolling constant divided by the square of the vessel'"'"'s rolling period. The rolling period is determined by means of a gravity sensor whose output is an electrical signal corresponding to the instantaneous magnitude and direction of the roll angle. Electronic level adjustment and gain selection means are also provided, to compensate for the fact that the stability indicator may often be installed with the gravity sensor off-horizontal. The signal from the gravity sensor is input into a data processor that computes the rolling period by first analyzing the roll angle signal to establish a zero level and threshold levels above and below the zero level. The rolling period is then determined to be the time required for the roll angle to change from the positive threshold, to a value less than the negative threshold, and back to the positive threshold again. Successive rolling periods are averaged by means of a recursive filter, and the average rolling period is used to determine GM. In another embodiment of the present invention, the stability indicator includes means for calculating two average rolling periods. The first average rolling period is determined by averaging a fixed number of successive rolling periods, and the second average rolling period is determined by averaging a selectable number of successive rolling periods. First and second GM values are calculated based on the first and second average rolling periods respectively. Means are also included for providing a warning when the first GM value is less than an alarm level, and for displaying the second GM value.
22 Citations
15 Claims
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1. A stability indicator for a marine vessel, comprising:
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sensor means for producing a first signal having a continuously variable characteristic, such as voltage magnitude, that continuously varies in a predetermined manner as the roll angle of the vessel continuously varies, such that the instantaneous value of the roll angle may be determined by measuring the instantaneous value of said characteristic; and processing means including means for receiving said first signal and for repeatedly measuring said characteristic over a period of time to thereby determine a plurality of instantaneous roll angle values over the period of time, means for determining the vessel'"'"'s rolling period based on said plurality of roll angle values, and means for determining a GM value equal to the square of the vessel'"'"'s beam length times the square of the vessel'"'"'s rolling constant divided by the square of the vessel'"'"'s rolling period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A stability indicator for a marine vessel, comprising:
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sensor means for producing a signal corresponding to the instantaneous value of the roll angle of the vessel, the sensor means including level adjustment means for adjusting the average level of said signal such that said average level is approximately equal to a fixed reference level; and processing means responsive to said signal for determining the vessel'"'"'s rolling period and a GM value based on the rolling period.
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14. A stability indicator for a marine vessel, comprising:
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sensor means for producing a signal corresponding to the value of the instantaneous roll angle of the vessel; processing means responsive to said signal for determining the vessel'"'"'s rolling period and a GM value based on the rolling period, the processing means including means for sampling said signal, means for determining a zero level corresponding to the average value of the sampled signal, means for determining first and second threshold levels spaced apart from the zero level on opposite sides thereof, the magnitude of the difference between the first threshold level and the zero level being a predetermined function of the average absolute difference between the sampled first signal and the zero level, and means for determining the vessel'"'"'s rolling period by determining the length of a time interval that begins when the sampled signal changes from a value on one side of the first threshold level to a value on the opposite side of the first threshold level and that ends at the next subsequent time at which the sampled signal changes from a value on said one side of the first threshold level to a value on said opposite side of the first threshold level, provided that the sampled signal crossed the second threshold level during said time interval. - View Dependent Claims (15)
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Specification