What is gom in ship stability


  • Ship Stability – Understanding Intact Stability of Ships
  • What is Stability requirements for Grain Loading?
  • What is Stability requirements for Grain Loading? Before loading bulk grain the master shall, if so required by the Contracting Government of the country of the port of loading, demonstrate the ability of the ship at all stages of any voyage to comply with the stability criteria required by this section. After loading, the master shall ensure that the ship is upright before proceeding to sea.

    Stowage of bulk grain as per grain code All necessary and reasonable trimming shall be performed to level all free grain surfaces and to minimize the effect of grain shifting. In any filled compartment, trimmed, the bulk grain shall be trimmed so as to fill all spaces under the decks and hatch covers to the maximum extent possible.

    In any filled compartment, untrimmed, the bulk grain shall be filled to the maximum extent possible in way of the hatch opening but may be at its natural angle of repose outside the periphery of the hatch opening.

    If there is no bulk grain or other cargo above a lower cargo space containing grain, the hatch covers shall be secured in an approved manner having regard to the mass and permanent arrangements provided for securing such covers. After loading, all free grain surfaces in partly filled compartments shall be level.

    In filled compartments, trimmed; filled compartments, untrimmed; and partly filled compartments, longitudinal divisions may be installed as a device to reduce the adverse heeling effect of grain shift provided that: The division is grain-tight; The construction meets the requirements of raincode.

    Note :- This Code applies to ships regardless of size, including those of less than tons gross tonnage, engaged in the carriage of grain in bulk, to which part C of chapter VI of the SOLAS Convention , as amended, applies. The term grain covers wheat, maize corn , oats, rye, barley, rice, pulses, seeds and processed forms thereof, whose behavior is similar to that of grain in its natural state. The term filled compartment, trimmed, refers to any cargo space in which, after loading and trimming as required under grain code, the bulk grain is at its highest possible level The term filled compartment, untrimmed, refers to a cargo space which is filled to the maximum extent possible in way of the hatch opening but which has not been trimmed outside the periphery of the hatch opening either by the provisions of grain code for all ships or for specially suitable compartments.

    The term partly filled compartment refers to any cargo space wherein the bulk grain is not loaded in the manner prescribed in grain code i.

    But let us imagine we together built a ship. Or something looking like a ship. A smaller one may be. With all our efforts, we put this small ship in the water. What will happen? Will the Ship sink or float Will the ship tilt list on starboard side or port side Will the ship have any trim or not.

    If yes, will the trim be by the head or by astern? If I want to know the answers to these questions, one thing is for sure. We need to be able to understand the language of ship stability. Trust me, I know. But not if you know the basics of ship stability. Once you know these basics, all other parts of ship stability will be as easy as eating a pancake. And I am talking about most basics things here.

    Understanding these basics forms the foundation of ship stability. In this post, I will discuss 6 of these basic things of ship stability. Let us start. Archemidies Principle Why does a small metal ball sink in water but not ship? Probably the first question that a Pre-sea cadet is asked during his training. While the question is quite basic, the answer forms the foundation of ship stability.

    The answer lies in the Archimedes principle. So what exactly is Archimedes principle? As per Archimedes principle A body wholly or partially immersed in a liquid is subject to an upthrust equal to the weight of the liquid displaced by the body. Let us first understand two keywords in the Archimedes principle.

    Upthrust Liquid displaced Upthrust Try to force a ball down into the water. You will feel a force stopping you from doing that. This is the upthrust we are talking about in Archimedes principle. This upthrust will be there on any object you place in water. Liquid displaced When we place any object into the water, that object would displace some water.

    I bet everyone knows it because even the birds know it. Remember the story of thirsty crow? So if we drop a stone in a jar completely filled with water, some water would spill out of the jar because the stone has displaced some water. The volume of water displaced would be equal the volume of the stone. Now let us see what Archimedes principle is trying to say? It is giving us a way to calculate the amount of upthrust that an object will feel when immersed in water or in any liquid.

    This upthrust will be equal to the weight not volume of liquid displaced by the object. How do ships float? So if we have to make something float, all we have to do is to make sure that it displaces more water than its own weight. And we have a solid cube of T weight made of same material. If both are put in water, while the ball will sink, the ship would float. The weight is same, the material is same and both are placed in the same water.

    As the weight of both is same, the downward gravitational force acting on both is same. But the upthrust acting on the ship will be more than that acting on the ball.

    Let us see why? The upthrust acting on the steel cube will be T. As the weight of the cube downward force is T, the cube will continue to move downwards and will sink. Now let us see the forces on a ship with lightweight of T. A ship of this light weight is generally of the approximate size of Length: meters Breadth: 30 Meters Height from keel to the main deck: 20 meters If it is submerged to its full height, it would displace m3 m x 30m x 20m x 0.

    This is considering the block coefficient of the ship is 0. This means that the upthrust acting on the ship would be T. The downward force is same as was for the steel cube.

    So why did the ship float while the steel cube sank? That is because the upthrust Buoyancy for the ship is much more than that of the cube of the same weight. Watch this simple experiment and you would understand.

    Buoyancy We saw that the ship in the example was able to generate T of buoyancy when immersed up to the deck line. As the weight of the ship was T, this means that the ship will have a net upward force of T.

    This upward force will keep on raising the ship until the upthrust is equal to the weight of the ship. So at the equilibrium, the upthrust buoyancy will be equal to the weight of the ship which is T. The remaining buoyancy of T will act as reserve buoyancy.

    So when a ship is at rest, the upthrust buoyancy acting on the ship will be equal to the gravitational force acting on the ship. When we add a weight on the ship, this equilibrium is offset as the gravitational force increases. This will cause the ship to sink, till the time buoyancy becomes equal to the downward gravitational force. In short, if a ship will float or sink, how much will it sink and how will it float is the function of these two forces acting in opposite direction Upward-acting force of buoyancy Downward acting gravitational force 4.

    Center of Gravity The center of gravity of any object is the point on that body at which the total weight of the object is assumed to be acting vertically downwards. This point is an imaginary point. For objects in uniform shapes and made of a uniform material, knowing the center of gravity is an easy task. For these objects, the center of gravity is the centroid of the shape.

    For objects of irregular shape such as ships, the center of gravity is again the centroid of this irregular shape. But in this case, it is too difficult to find the centroid of the shape. But what is the significance of center of gravity of any object?

    First, for the stability calculations, this is the point where we can consider the gravitational force acting downwards. Second, this is the point from which the object will balance. If you still have any doubt over what center of gravity is, this considerably old video will definitely help.

    So where is the center of gravity acting on a ship and how can we know its location? Center of gravity of the ship is measured from three dimensions. From the centerline of the ship The first dimension is knowing the location of the center of gravity from the centerline of the ship.

    If the COG is on the centerline, the ship will be upright no list. So guess which side the ship would be listed if the COG is as indicated in the above photo? More away the COG is from the centerline, the larger will the ship be listed. Sometimes this distance is also referred as TCG transverse center of gravity Location from the forward aft or midship of the ship The second dimension is the location of COG from the forward perpendicular, aft perpendicular or from the midship of the ship.

    This term is called Longitudinal center of gravity or LCG. LCG is tabulated in the hydrostatic particulars of the ship for different drafts and tr The location of LCG decides which way the ship will be trimmed. If the location of LCG is exactly at the midship, the ship will have no trim.

    But if the LCG is forward of the midship, the ship will be trimmed by the head. Same way, if the LCG is aft of the midship, ship will be trimmed by the stern. If the heavier weights are loaded on the top part of the ship, then COG of the ship will be towards the top of the vessel. In this case, KG of the ship will be a larger value. If the heavier weights are loaded on the bottom part of the ship, COG will be towards the bottom of the ship and KG of the ship will be a smaller value.

    We have already discussed that TCG value decides to the list of the ship and LCG value corresponds to the trim of the ship. To understand the significance of KG, let me ask you a question. If you are given a task to carry a cube weighing few kilos attached with a rod, how will you hold it? From the rod position A or from the cube position B? I am sure you would agree that it is much easier to hold the cube than to hold the rod.

    Same goes with the ship and any other object. So in the case of ships, larger the KG, less stable the ship would be. Center of Buoyancy Just as the weight of the vessel was assumed to act downward through the center of gravity, the buoyancy force is assumed to act vertically upwards through a single point as well. This point is known as the center of buoyancy.

    The center of buoyancy is the centroid of the underwater part of the vessel. For the sake of understanding, we can say that center of buoyancy is the center of gravity of the underwater volume of the ship. As with the COG, COB can also be measured from three dimensions but measuring it from the centerline of the ship has no significance.

    With all our efforts, we put this small ship in the water.

    Ship Stability – Understanding Intact Stability of Ships

    What will happen? Will the Ship sink or float Will the ship tilt list on starboard side or port side Will the ship have any trim or not.

    If yes, will the trim be by the head or by astern? If I want to know the answers to these questions, one thing is for sure. We need to be able to understand the language of ship stability.

    Trust me, I know. But not if you know the basics of ship stability. Once you know these basics, all other parts of ship stability will be as easy as eating a pancake. And I am talking about most basics things here.

    Understanding these basics forms the foundation of ship stability. In this post, I will discuss 6 of these basic things of ship stability. Let us start. Archemidies Principle Why does a small metal ball sink in water but not ship? Probably the first question that a Pre-sea cadet is asked during his training. While the question is quite basic, the answer forms the foundation of ship stability.

    The answer lies in the Archimedes principle. So what exactly is Archimedes principle? As per Archimedes principle A body wholly or partially immersed in a liquid is subject to an upthrust equal to the weight of the liquid displaced by the body.

    Let us first understand two keywords in the Archimedes principle. Upthrust Liquid displaced Upthrust Try to force a ball down into the water. You will feel a force stopping you from doing that. This is the upthrust we are talking about in Archimedes principle. This upthrust will be there on any object you place in water. Liquid displaced When we place any object into the water, that object would displace some water.

    I bet everyone knows it because even the birds know it. Remember the story of thirsty crow? So if we drop a stone in a jar completely filled with water, some water would spill out of the jar because the stone has displaced some water. The volume of water displaced would be equal the volume of the stone. Now let us see what Archimedes principle is trying to say?

    It is giving us a way to calculate the amount of upthrust that an object will feel when immersed in water or in any liquid. This upthrust will be equal to the weight not volume of liquid displaced by the object. How do ships float?

    What is Stability requirements for Grain Loading?

    So if we have to make something float, all we have to do is to make sure that it displaces more water than its own weight. And we have a solid cube of T weight made of same material. If both are put in water, while the ball will sink, the ship would float. The weight is same, the material is same and both are placed in the same water. As the weight of both is same, the downward gravitational force acting on both is same.

    But the upthrust acting on the ship will be more than that acting on the ball. Let us see why? The upthrust acting on the steel cube will be T. As the weight of the cube downward force is T, the cube will continue to move downwards and will sink. Now let us see the forces on a ship with lightweight of T. A ship of this light weight is generally of the approximate size of Length: meters Breadth: 30 Meters Height from keel to the main deck: 20 meters If it is submerged to its full height, it would displace m3 m x 30m x 20m x 0.

    This is considering the block coefficient of the ship is 0. This means that the upthrust acting on the ship would be T. The downward force is same as was for the steel cube. So why did the ship float while the steel cube sank?

    That is because the upthrust Buoyancy for the ship is much more than that of the cube of the same weight. Watch this simple experiment and you would understand. Buoyancy We saw that the ship in the example was able to generate T of buoyancy when immersed up to the deck line. As the weight of the ship was T, this means that the ship will have a net upward force of T. This upward force will keep on raising the ship until the upthrust is equal to the weight of the ship.

    So at the equilibrium, the upthrust buoyancy will be equal to the weight of the ship which is T. The remaining buoyancy of T will act as reserve buoyancy. If there is no bulk grain or other cargo above a lower cargo space containing grain, the hatch covers shall be secured in an approved manner having regard to the mass and permanent arrangements provided for securing such covers.

    After loading, all free grain surfaces in partly filled compartments shall be level. In filled compartments, trimmed; filled compartments, untrimmed; and partly filled compartments, longitudinal divisions may be installed as a device to reduce the adverse heeling effect of grain shift provided that: The division is grain-tight; The construction meets the requirements of raincode. Note :- This Code applies to ships regardless of size, including those of less than tons gross tonnage, engaged in the carriage of grain in bulk, to which part C of chapter VI of the SOLAS Conventionas amended, applies.

    The term grain covers wheat, maize cornoats, rye, barley, rice, pulses, seeds and processed forms thereof, whose behavior is similar to that of grain in its natural state. The term filled compartment, trimmed, refers to any cargo space in which, after loading and trimming as required under grain code, the bulk grain is at its highest possible level The term filled compartment, untrimmed, refers to a cargo space which is filled to the maximum extent possible in way of the hatch opening but which has not been trimmed outside the periphery of the hatch opening either by the provisions of grain code for all ships or for specially suitable compartments.


    What is gom in ship stability