A new resolution on energy-efficiency regulation of ships was adopted at the 65th session of the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO),...
The fatal results of excessive roll and pitch are as nofollows:
1. First, the ship upsetting arising from excessive inclination due to roll.
2. In the next place, the hull structure damage because of sharp roll and pitch as well as the violent movement of bulk cargoes, or even worse the hull might break.
3. Still next, the affection on the propulsion plant, i. e. the increase of water resistance and the reduction of speed by reason of roll and pitch.
4. Then, the affection on proper operation of various kinds of machines and instruments.
5. Last of all, the hard working condition which causes the crew to be seasick.
Therefore, we have to take roll and pitch into our consideration during the design
stage, for they are closely related to the whole seakeeping performance.
As you know, the roll period is greatly concerned with the initial metacentric
height and, in some degree, stability is contrary to roll. It seems to be strange that violent roll, as many people might think, is not derived from poor stability.
So far different stabilizing units have been invented, and found wide application to
decreasing roll and pitch. Common stabilizing units now in practical use are bilge keels, stabilizers and wing,buoyant tanks.
Floodability states the ability for a vessel to keep afloat with sufficient floatability, stability and other seakeeping performances in case one or several compartments are flooded. Should sea damage take place, reserve buoyance would be the principal condition to keep a vessel afloat. With the help of the watertight bulkheads and decks which separate the inside of hull into a number of compartments and spaces, reserve buoyance enough is to be retained so that the intake of sea water may be confined to the damaged compartment without water pouring into the adjacent compartments.
The last seakeeping performance that we are coming to is maneuverability, which refers to the ability for a vessel to retain or change its course in accordance with the pilot's intention.
Maneuverability is composed of two abilities, that is, the directional stability and
the turning ability. The former indicates the ability for a vessel to keep to its given
course, while the latter sets forth the ability for a vessel to change its course. Ocean
going vessels require strict directional stability, whereas short-range ships ask for a
better turning ability. Moreover, the smaller the turning circle of vessels, the better their
In the guarantee of vessel maneuverability, a steering gear of fine quality is to be provided, rudder being its primary component.