‘A’ Frame – A support structure to provide rigidity to the shaft of a twin-propeller construction. It is shaped like a turned-over ‘A’, hence its name, where the propeller shaft is supported at the apex of the structure.Aft Peak Tank – A water tank set right aft of the vessel. It will either be a designated freshwater tank or a ballast water tank used for adjusting the ship’s trim.Beam Knees – Triangular steel plates secured between beams or half-beams and the side frames. They tend to compensate for racking stresses and localised stresses from heavyweights.Beams – These are usually in … [Read more...]
The Inclining Experiment – Ascertain the GM of Vessel
Purpose Ship’s stability calculations not only rely on the ship’s geometry but also on the knowledge of where the ship’s centre of gravity (G) is positioned. Although the distance of G from the keel can be ascertained for various conditions that the ship may be in, it is essential that it is accurately known for one specified ship condition.To this end, the need to carry out an inclining experiment becomes necessary and from this, two facts should become known:the displacement; and the position of G in a known ship’s condition.The inclining test is carried out to find the … [Read more...]
Ship’s Log and Log Distance
An instrument for measuring the speed of a ship through water is called a ship's, or maritime, log. The same word is also applied to the daily record of a ship, though it is more properly termed a logbook. History In the years of sailing ships, the Dutchman's log was an early method of calculating ship speed. An object that would float was thrown into the water near the forward part of a ship. In the after, or rear, section, a sailor with a sandglass noted the time taken for the ship to pass the object floating in the water. From the time and the known distance between the two points on the … [Read more...]
The Marine Chronometer
The spring-driven marine chronometer is a precision timepiece used aboard ship to provide accurate time for celestial observations. A chronometer differs from a spring-driven watch principally in that it contains a variable lever device to maintain even pressure on the mainspring, and a special balance designed to compensate for temperature variations.A spring-driven chronometer is set approximately to Greenwich mean time (GMT) and is not reset until the instrument is overhauled and cleaned, usually at three-year intervals.The difference between GMT obtained directly from a radio time … [Read more...]
Ship’s Magnetic Compass – Dry and Wet Compass with their care, maintenance and bubble removal
As per Chapter V of SOLAS 74, as amended, a magnetic compass is a compulsory part of the shipborne navigational equipment. This is in addition to the gyro compass & suitably placed repeaters on the ship. This is so primarily because of the reliable dependence one can place on the magnetic compass, as a standby compass in the event of failure of electrical power on board. The regulation also stipulates that the magnetic compass should be properly adjusted and a table or curve of deviations is available on board at all times.Our intention is only to give you a brief description and … [Read more...]
Gyro Compass – Basic Principle, Operation and Usage on Ships
Gyro Compass is a navigational compass containing gyroscope motor that registers the direction of true north along the surface of the earth and it does not depend on magnetism. or A compass with a motorized gyroscope whose angular momemtum interacts with the force produced by the earth's rotation to maintain a north-south orientation of the gyroscopic spin axis, therby providing a stable directional reference. The Principle of Gyroscope A gyroscope consists of a spinning wheel or rotor contained within gimbals which permit movement about three mutually perpendicular axes, known as the … [Read more...]
Coefficients of Form – Ship’s Waterplane, Block, Midship and Prismatic Coefficient
The Coefficient of Form shows the relationship between the actual form of the ship and the dimensions of the ship.Waterplane Area Coefficient (Cw) It is the ratio of the actual area of the waterplane to the product of the length and breadth of the ship. As seen below, the area of the ship’s waterplane is shown shaded and a rectangle having the same length and breadth of the ship:Coefficient of fineness (Cw) = Area of waterplane ÷ (Length x Breadth) Example: Q. Find the area of the waterplane of a ship 200 meters long, 30 meters beam, which has a coefficient of fineness of … [Read more...]
The Aneroid Barometer and How to use it…
A barometer is an instrument for measuring the pressure of the air, due to the weight of the column of air above it. As the earth’s atmosphere gets thinner with increasing height, it follows that as we ascend from sea level and low-lying parts of the earth’s surface, the weight of the air will decrease. That is, the pressure will fall.An ordinary clock face type barometer placed in your car will give an estimate of the changes in altitude as you drive through the country. If we use rough figures, we can say that the reading decreases by three hectopascals for each twenty-five … [Read more...]
UNCLOS – Salient Features, Objectives, Maritime Zones, Passages and Duties
United Nations Convention on the Law of the Sea (UNCLOS)UNCLOS lays down a comprehensive regime of law and order in the world's oceans and seas. The 1982 convention was signed by 117 states and it establishes rules governing all uses of the ocean and its resources. The convention also provides the framework for the development of a specific area of law of the sea. The convention is a lengthy document having 446 articles group in 7 parts in 9 annexes. UNCLOS came into force internationally on 16th Nov 1994.Baseline As otherwise provided in the UNCLOS convention, the … [Read more...]
Master Pilot Exchange – Duties, Responsibilities and Elements of effective Relationship
It is a given fact that invariably pilotage is compulsory and the majority of accidents occurring during berthing occur with a pilot on the bridge. No berthing guide would be complete without reference to the master-pilot relationship.Pilotage Why are Pilots engaged? For their expertise in navigating in close proximity to land in narrow channels. For their ability to anticipate accurately the effects of currents and tidal influences. For their understanding of local traffic. For their ability to work effectively with the local VTS. For their language ability when … [Read more...]