Quote:
Originally Posted by VenezianBlau 87
If a 20,000 ton displacement ship sinks to xx,000 feet to the sea floor, will it still weigh out at 20,000 tons at that depth? Assume no buoyant compartments or similar conditions.
Thanks,
Bob
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displacement of a vessel is an indirect method for assessing the weight of the ship by calculating the weight of the water which is replaced or pushed aside by the ships hull when it is floating, To laymen and for most purposes the weight and mass are rarely considered to be the separate metrics that they really are
a floating 20k ton displacement means that 20k tons of water is pushed aside to support the vessel
weight and mass are 2 different but related quantities
in the British Engineering System mass is measured in slugs
on the earths surface at nominal sea-level
20,000T/32 = 632k slugs
when the ship sinks no matter where it is, as long as it doesn't break up, it always has 632k slugs of mass
when it sinks the weight varies according to Newton F = GMM/r^2 so yes the gravitational pull on the solid structure decreases proportional to r^2
but
on the surface the hull is filled w/ relatively light weight air
at depth the air is replaced by much denser and heavier water so the next q is do you count the the mass of the water inside the sunken vessel in your estimation, for some purposes the answer is, yes, for instance suppose you wanted to know the force necessary to move the boat laterally or to lift it before hitting bottom. Here the interior volume of water is being moved along w/ the ship structure so it is necessary to account for it.
but
the answer most of the time is, no, as usually what you really want to know is the mass of the solid structure + tankage of the vessel whether it is afloat or not
in the vernacular weight and mass are often bandied about w/ no true concern for their actual definition