UNIT 2 MARINE VEHICLES Marine vehicles operate in or on water, for the purposes of transportation, recovery of natural resources, warfare, research or pleasure. This makes marine vehicles very important in the maritime industry. Like road vehicles differ, so does marine vehicles. In this unit, we shall explore the various classes of marine vehicles existing.
What You Will Learn Identify the classes of marine vehicles at work in the maritime industry; Categorize ships by the: – Jobs they are used for; – Type of freight aboard; – Areas of operation.
Classes of Marine Vehicles Generally, marine vehicles are in three (3) groups: – Surface vehicles; – Submarine vehicles; – Offshore structures.
Surface Vehicles Ships in this class, have a portion of the hull in water, and the remaining out of water. Hence, such ships are visible in operation. All ships used in the merchant navy, are of this class.
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Ships in the class of surface vehicles can be put into three (3) groups: – Displacement hull ships; – Planing hull ships; – High performance ships.
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Displacement hull ships have their hulls partly immersed in water. They float because their weight is entirely supported by the force of water. Hence they experience lot of resistance from water and consequently, move slowly. However, they carry more cargo.
Cont’d….. Displacement hull surface ships are in three (3) forms: Monohulls Catamarans Trimarans
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In terms of speed, trimarans are faster than catamarans and monohulls. And catamarans are also faster than monohulls. In terms of cargo carriage, monohulls would carry much more load than catamarans and trimarans. And catamarans would also carry a little more load than trimarans.
Cont’d….. Planing hull ships at normal speeds, operate as monohull surface ships. However, at high or cruising speeds, a lift is generate which enables a greater portion of the underwater hull section to come out of water leaving a small portion of the underwater hull area planing on the water surface. Meaning, in operation planing hull ships are subjected to minimum water resistance when compared with displacement hull ships.
Cont’d….. This makes planing hull ships faster than displacement hull ships. But planing hull ships cannot carry much cargo as displacement hull ships do. This is because with much cargo, the load on the ship is increased, and planing hull is unable to generate the appropriate lift. Hence, planing hull ships are smaller in size and often employed as pleasure boats.
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High performance ships in normal operation can be likened to displacement hulls. But at designed cruising speeds, their hulls are completely out of water. This reduces water resistance to approximately zero. Ensuring that ships in this category, sail faster than those discussed previously.
Cont’d…… High performance ships exist in three (3) forms: Hydrofoils Surface Effect Ships (e.g. Hovercrafts) Small Waterplane Area Twin Ships (SWATH)
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Submarine Vehicles Marine vehicles in this category are designed to operate below the surface of water. They are in two (2) forms: Conventional submarines Diving bells Conventional submarines are for military purposes only.
Cont’d….. Diving bells are experimental basins which could house a person or an equipment. It is let down into water for research purposes.
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Offshore Structures Ships in this category are employed in the offshore industry. They serve as platforms for the recovery of natural resources (e.g. crude oil) in some water bodies and installation of structures on water (e.g. VLFS). Some operate as ships (i.e. they can move on their own) whilst others need to be moved to location.
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Monohull Ships Monohull ships can be classified based on the kind of service they provide:
Merchant Ships
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Industrial Ships
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Fishing Ships
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Governmental Ships Conventional submarines
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Private Ships
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Summary Several ships exist and they vary based on size, cargo capacity and type, hull design, etc. When choosing a ship, decision has to be based primarily on the size and speed of the ship, and type of cargo to be transported.