Question

cargo is loaded at the buttom of the ship why​

Answer 1

Answer:

The answer is: That is not so in all cases. It has to do with the stability of the vessel, which I’m not going to explain in detail, it can be quite complicated.

As a rule of thumb, it is advantageous to get the combined center CG of gravity (of ship and cargo) as low in the ship as possible, but only to a certain extend. The CG should be below the center of buoyancy (BC), which is the point where all the upward forces “acts” on the ship to keep it afloat.

Here a couple of examples which might give you some idea of what I talking about:

Take a coaster say 60 meters long, load the vessel down to maximum draft, by placing the cargo on the deck. The vessel will definitely capsize. The vessel is unstable.

Take the same vessel and put all the steel plates at the bottom of the hold and the vessel will most likely have excess stability, meaning it will be very uncomfortable for the crew to be on board when in waves. The horizontal acceleration forces at the bridge could be unbearable.

A compromise between the two extremes above could be to put part of the cargo on the deck and part on the bottom. Or if that is not possible, reduce cargo, leave the rest on the deck, and fill ballast water in the bottom tanks, now the vessel could be made stable, but you lose income due to the reduced cargo.

On passenger ships, the stability must be such that the vessel rolls softly, yet stable enough so it won't capsize, otherwise, the passengers get seasick! In order to achieve this, the big passenger ships are equipped with “wings” beneath the waterline, these “wings” can be turned mechanically so they artificially decrease the stability to a comfortable level.

Answer 2

Answer:

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Explanation:

it is not always that way. Some specialized purpose ships and barges have their cargo loaded on top of their main deck for easy loading and unloading their cargoes. Such vessels are designed to have high KM value that with proper stowage plan, the final GM will still have positive value which is enough to prevent the vessel to thumble during a voyage.