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Stability
Seamanship Midterm 1
| Term | Definition |
|---|---|
| stable | If a ship is this, it rights itself when it is moved out of a horizontal plane |
| unstable | If a ship was this, an external force would continue to roll the ship over, rather than allow it to come back to the vertical, a most undesirable state of affairs |
| stiff | A ship with a great deal of weight in the bottom, and none in the upper parts of the hull, might be termed this |
| tender | A ship might be called this if it had too much weight in the upper part of the hull, and insufficient bottom weight, might equally well be stable, but the period of roll would be very slow. |
| stability | Important elements in the calculation of the ship’s ___ will be the centre of gravity and the centre of buoyancy. |
| metacentre | The point at which the vertical line representing the force of buoyancy acting on an inclined ship cuts the centre line of the ship |
| Trim | It's the difference between the drafts of the ship at the bow and stern and will dictate whether the propeller is adequately submerged, and ensure the bow does not slam into oncoming waves. |
| Centre of Buoyancy | the centroid of the underwater volume of the ship. |
| Centre of Gravity | the center of mass of the ship. |
| negative stability | G is above M |
| positive stability | G is below M |
| neutral stability | G is coincident with M |
| Trim | The longitudinal equivalent of list |
| By the stern | When aft draft is greater than forward draft, trim is positive or "__" |
| By the bow/head | When forward draft is greater than aft draft, trim is negative or "___" |
| MCTC | Change in trim is measured by this |
| load lines | the marks punched into and painted on the sides of a merchant vessel. |
| freeboard deck | The uppermost complete deck exposed to weather and sea. |
| freeboard | It is the vertical distance measured amidships, from the upper edge of the deck line, to the upper edge of the related load line |
| Samuel Plimsoll | Advocated the creation of legislation about load lines |
| Winter Load line | This is one forty-eighth of the summer load draft below the summer load line. |
| Tropical Load line | This is one forty-eighth of the summer load draft above the summer load line. |
| Draft | The vertical distance between the waterline and the bottom of the hull(keel). |
| Mean Draft | Obtained by calculating mean (average) of fwd (bow) and aft (stern) draft. |