Your vessel is preparing to lift a weight of 30 tons with a boom whose head is 30 feet from the ship's centerline. The ship's displacement not including the weight lifted is 8,790 tons. KM is 21.5 ft, KG is 20.5 ft. What would be the angle of list when the weight is lifted?
• Transverse shift of center of gravity (G) when lifting a weight with a boom off the centerline • Formula for GM (metacentric height) and how it relates to small-angle list: ( ,\tan(\theta) = \frac{GZ}{GM} ,) • How to compute the horizontal movement of G using the virtual work method: ( w \times d = \Delta \times GG_1 ,)
• How does the lifted weight act on the ship once it is just clear of the deck: as part of the ship’s displacement or as an external load? • What is the horizontal lever arm of the weight relative to the ship’s original centerline, and how does that create a transverse shift in the ship’s center of gravity? • Once you find the new transverse position of G, how do you convert that off-center distance into an angle of list using GM and small-angle stability relationships?
• Be sure you are using the total displacement including the lifted weight when you relate ( w \times d ) to ( \Delta \times GG_1 ). • Confirm that you are working in consistent units (all distances in feet, all weights/forces in tons). • After finding ( \tan(\theta) ), double-check that the angle you compute is in degrees, not radians, before comparing to the multiple-choice options.
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