Training / June 6th

The stability of the ship is a very important aspect of keeping the ship safe.  Not only does the proper management of the stability make the ride of the ship more comfortable, it can keep the ship from listing to one side or the other.  Most importantly, keeping the stability of the ship in the proper range, keeps the ship from rolling over.

Ships are designed to float upright when empty.  When you start to put things into the ship, you need to put the heavy things on the bottom and the light things on the top.  This way the ship will continue to float in the upright position.  If you put all of the heavy things on the top of the ship, it tends to roll the ship over. 

This is all an over simplification, but in general is true.  For comfort, we don’t put all the heavy weight in the bottom or the ship would roll back and forth to the swell very violently and make us very uncomfortable. 

When putting weight onto the ship, we also need to balance the weight from one side to the other, and from the bow to the stern.  From side to side, we want the ship up right.  From the bow to the stern, we want the ship either on an even keel or slightly down at the stern. 

When the stern goes down, the bow comes up.  If the stern is allowed to go down too much, the draft of the ship can be so great that the harbors are not deep enough for the ship.  If the ship is allowed to go down at the bow, the rudder and propeller get out of the water, and the ship will maneuver badly. 

Besides the cargo that is put into the ship, fuel, water and ballast are the other main weights that are moved around the ship and that change.  Whenever we move a weight, or add or subtract a weight, we calculate its effect on the ship mean draft and forward and after draft to make sure we are where we want to be.

We also calculate the GM (distance from the center of gravity of the vessel to the medicenter) of the ship which tells us how much the ship has to right itself when pushed over by the wind or a swell.  We keep the GM between 2 and 4 feet whenever possible.