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Bounding Box: Determining Where a Ship Will Fit



The idea of a bounding box is everywhere in geometry and industry. Designers and engineers need to know if something will fit in the available space.

Sometimes it isn’t a matter of if it will fit in its final location but if it will fit through an opening like a door or hatchway to reach the final location.

In these cases it is referred to as a minimum bounding box. The object must fit into an imaginary box of a certain dimension so it can be moved into the final location without interference.

Shipbuilders and naval architects use this imaginary box to be sure a new ship can fit through constricted areas like locks in canals. Locks raise and lower a ship by filling or draining a watertight enclosure so it can reach a higher or lower water level in a canal or river.

Of course a ship must fit into this watertight box or it will not be able to pass through to the other side.

So a ship must be shorter and narrower than the lock which in nautical terms means that it must be limited in length and beam.

Now we have two dimensions covered, length and width. The next step is to add the third dimension.

Since a ship floats on top of the water we will divide the third dimension of height into the area above the water and the area below the water.

Below the water, or waterline as naval architects call it, there is the underwater portion of the ship’s hull. The distance from the waterline to the bottom of the hull, or keel is called the ship’s draft.

Draft is important since bad things can happen to a ship if it hits the bottom when it is moving. It can get stuck or worse if it damages the hull.

So now we will look at the top of the ship from the waterline to the top of the tallest point. This measurement is called air draft. Air draft is like draft but going up instead of down.

Air draft is important since ships must be able to pass safely under bridges.

All of these variables combine when a designer measures the locks, draft, and air draft of a particular route the ship must take to pick up and deliver cargo or passengers.

That is the reason many ships are designed for specific routes and cargo. Ships that are built to travel on a certain route are called classed ships.

There are many classes of ships and each one is built to the largest size possible so it can operate at full capacity and make the most profit from the journey.

The minimum bounding box, a simple three dimensional measurement, makes all of this possible.

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