The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship. It is the distance between center of gravity (c) and Metacenter. It is the measure if static stability of floating body. Large the metacentric height more is the stability. AIM: To determine the meta-centric height and position of the meta-centric height with angle of heel of ship model. APPARATUS REQUIRED: Water tank.

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An ideal boat strikes a balance.

A larger metacentric height implies greater initial stability against overturning. Technically, there are different metacentric heights for any combination of pitch and roll motion, depending on the moment of inertia of the waterplane area of the ship around the axis of rotation under determinationn, but they are normally only calculated and stated as specific values for the limiting pure pitch and roll motion.

The righting arm known also as GZ — see diagram: These are gravity acting downwards at the centre of mass and the same magnitude force acting upwards through the centre of buoyancy, and through the metacentre above it.

This is known as the free surface effect. KM is the distance from the keel to the metacentre. It is the interplay of potential and kinetic energy that results in the ship having a natural rolling frequency.

Experiment – Various Parts of Hydraulic Bench. The metacentre can be calculated using the formulae: Calibration Of Rectangular Notch. Sailing vessels are designed to operate with a higher degree of heel than motorized vessels and the righting moment at extreme angles is of high importance. Desirable and Undesirable Characteristics of Offshore Yachts.

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The period of roll can be estimated from the following equation [2]. This is because the stiff vessel quickly responds to the sea as it attempts to assume the slope of the wave.


In the diagram, the two Bs show the centres of buoyancy of a ship in the upright and heeled conditions, and M is the metacentre. When an edge is tipped, the water rushes to that side, which exacerbates the tip even further.

Metacentres are usually separately calculated for transverse side dteermination side rolling motion and for lengthwise longitudinal pitching motion. As the hull rights, work is done either by its centre of mass falling, or by water falling to accommodate a rising centre of buoyancy, or both.

Seamanship in the age of sail. However, the center of buoyancy lies a depth below the surface of the water which corresponds to the plane. The righting couple on the ship is proportional to the horizontal distance between two equal forces.

Because the vessel displacement is constant, common practice is to simply graph the righting arm vs the angle of heel. If a ship floods, the loss of stability is caused by the increase in KB determiination, the centre of buoyancy, and the loss of waterplane area – thus a loss of the waterplane moment of inertia – which decreases the metacentric height.

Metacentric height

Metacentre is determined by the ratio between the inertia resistance of the boat and the volume of the boat. The piston tilted and suspended rod gave the angle of head, I noted the angle for respective displacements.

Worldwide Tonnage Gross tonnage Compensated gross tonnage Net tonnage. Similarly, the downflooding angle is the angle at which water will be able to flood deeper into the vessel.

The maximum righting moment is the maximum moment that could be applied to the vessel without causing it to capsize.

This is deternination to potential energy by raising the centre of mass of the hull with respect to the water level or by lowering the centre heibht buoyancy or both.

It is easily demonstrated that. The centre of buoyancy is at the centre of metacenyric of the volume of water that the hull displaces. As is easily demonstrated, the body’s new draft becomes. When a ship heelsthe centre of buoyancy of the ship moves laterally. Length overall Length between perpendiculars Length at the waterline. Coast Guard Technical computer program support accessed 20 December This potential energy will be released in order to right the hull and the heihgt attitude will be where it has the least magnitude.


The metacentre is considered to be fixed for small angles of heel; however, at larger angles of heel, the metacentre can no longer be considered fixed, and its metaxentric location must be found to calculate the ship’s stability.

Stability and Metacentric Height

Let and be the mean centers of these two volumes, and that of the whole volume. When the heitht is inclined, the fluid in the flooded volume will move to the lower side, shifting its centre of gravity toward the list, further extending the heeling force.

In such vessels, the rolling motion is not uncomfortable because of the moment of inertia of the tall mast and the aerodynamic damping of the sails. Retrieved from ” https: Deadweight tonnage Twenty-foot equivalent unit Intermodal containers.

The significance of this effect is proportional to the cube of the width of the tank or compartment, so two baffles separating the area into thirds will reduce the displacement of the center of gravity of the fluid by a factor of 9.

A simple extension of the previous argument reveals that if the body turns through a small angle about the -axis then the metacentric height is. It is necessary for the stability of a floating body, If metacenter is above center of gravity body will be stable because the restoring couple produced will shift the fo to its original position.

This is of significance in ship fuel tanks or ballast tanks, tanker cargo tanks, and in flooded or partially flooded compartments of damaged ships. Displacement Determinatio displacement Standard displacement Light displacement Normal displacement.