A plane landed on a ship for the first time in 1910 (Green, 1988, p.13). This marked the beginning of the development of aircraft carriers. Aircraft carriers are large warships used to carry airplanes. Aircraft carriers were developed to act as mobile airbases for use by the navies thereby providing a flexible means of launching planes for attacks from the sea. As such, aircraft carriers are designed to be so large that they resemble airports. With an aircraft carrier, the naval force can project airpower anywhere in the world without necessarily having to depend on local airbases to stage aircraft operations. All aircraft carriers have the same basic form and the hull looks like that of other large ships. The top deck is similar to an airport runaway and usually referred to as the flight deck. A deck located under the flight deck is the hangar deck used to store planes. A flight deck is just like an airport runaway. However, unlike in airports, the runaways of aircraft carriers are shorter. For this reason, an aircraft carrier has features that help planes in taking off and landing. When landing, arresting wires are used while catapults are used to help planes take off.
The earliest aircraft carriers were very small for example the U.S navy carrier was 160m while modern carriers can be as long as 360m. Small carriers can displace as little as 20,000 tons while large ones can displace up to 97,000 tons of water with the fastest carrier travelling at around 40 miles per hour. Apart from equipment such as arresting wires, catapult, elevators, launcher etc, the design of an aircraft carrier also allows for the provision of a lifting device: crane. There are quite a number of things to be lifted on the deck. However, most of the things such as simple loads can be lifted with simple movable cranes or material handling equipment. In order to lift heavier and critical loads such as a plane involved in a crash or a malfunctioning plane, it is important to have a specialized crane on board.
Although all crane lifts require pre-lift planning to determine factors such as load weight, rated capacity, crane configuration, and site conditions, some cranes require more extensive planning by design team; often referred to as “critical lifts”. Critical lifts, as opposed to ordinary lifts, require a more comprehensive lift plan to minimize the potential of either crane failure or catastrophic loss; or both. A critical lift plan includes information such as description of the lift; crane position and configuration; lift height; load radius; boom length and angle; size and weight of the load; percent of crane rated capacity; personnel involved; rigging plan; communication method; ground conditions; inspection procedures; and procedures for hoisting personnel (Hartford, 2008, p.1).
Statement of the Problem
Certain equipment requires that they are designed to suit a particular use. In a case like that of cranes, it can be found that there are so many varieties to be chosen from the manufacturers or distributors. However, certain circumstances call for a modification/customization of the common equipment for specialized cases. A crash crane to be used in an aircraft carrier is one such example. A delivery of the ideal crash crane is a product of so many factors. The question is what are these factors?
Objective of the study
This study is about assessment of factors affecting the choice of a crash crane for an aircraft carrier.
The general objective is to study the factors affecting the choice of a crash crane used in an aircraft carrier.
The specific objectives are
(i) To examine if cost affect the choice of a crash crane
(ii) To investigate if the existing technology affects the choice of a crash crane
(iii) To study if the manufacturer’s restrictions have an impact on the type of crash crane
(iv) To examine if the client’s nature of design have an impact on the manufacture of a crash crane
Significance of the study
This study will be of great significance to
(i) The government
(ii) The navy department
(iv) Design engineers
(v) Procurement personnel
(vi) Safety department
Limitations of the study
This study will be limited to the cranes used in aviation particularly those suited to the aircraft carriers. The study will cover only those cranes capable of lifting planes.
CHAPTER TWO: Literature Review
The crane is a primary machine used for vertical and overhead horizontal movements of materials, equipment and construction materials. A crane can be designed to offer several economic and safety advantages depending on area and work situations. The most common types of cranes are: crawler, hydraulic truck, lattice-boom truck, rough-terrain truck, all-terrain truck, heavy lift, modified cranes for heavy lifts, and tower. There are studes and statistics for cranes such as crane fatality data and nature of the fatality; and crane accidents and nature of accidents. Selection of cranes are usually informed by height of reach required, working envelope, maximum load, time, and duty cycle (Assakkaf, 2003, p.2-33).
They are built to 100-ton capacity and above and are built for lifting capability. However, they lack the heavier components for duty-cycle works. They are universal machines which incorporate heavier frames with heavy duty multiple clutches/brakes and more powerful systems for swinging. Crawler designs are good for quick changing of drum laggings which can be used to vary the torque or speed ratio of cables to the load. The time and cost to dismantle, investigate haul routes load, and reassemble the crane increases with increase in the size of the crane. To transport the largest crawler machines can require fifteen or even more truck trailer units. Although they have lower initial cost per rated lift capability, crawler cranes has one of the most expensive movements between jobs. As such, they are suited for jobs requiring long duration of usage at a given site (Assakkaf, 2003, p.2-33).
Hydraulic truck cranes
They have self-contained booms and their designs allow them to travel with their own power on highways with minimum dismantling. This feature ensures that there are minimum set-up delays. For jobs that require to be done in a few hours, a day or a few days, a hydraulic truck should be given a priority due to its ease of movement and minimum set-up time. Its hydraulic multi-section telescoping boom is part of a permanent part of the full revolving structure placed on a truck carrier. Three common power control arrangements are possible with hydraulic truck cranes. The first is where a single engine as both the truck and the crane power source, with a single cab used both to drive the truck and to operate the crane. The second is where a single engine is used to drive the truck and crane but with two separate cabs: one for driving the truck and the other for operating the crane. The third is where there are two separate engines and cabs for both the truck and the crane. These cranes have extendable triggers for stability. It is important to note that all mobile cranes are sensitive to stability and the rated loads are based on a level machine, ideal conditions no dynamic effects and calm air (Assakkaf, 2003, p.2-33).
Lattice-boom truck crane
It has a revolving superstructure mounted on a carrier/multi-axial truck with the advantage of lattice boom (a cable-suspended that acts as a compression member as opposed to bending member as in a telescoping, hydraulic boom). This model is lightweight meaning the machine can handle additional weight since the boom is not part of the weight to be lifted. It is easier to assemble and its light weight gives a less lattice-boom same hoisting capacity as a larger hydraulic crane. However, its disadvantage is time and effort required during disassembling and assembling them during transport and in addition the machine requires the use of another crane(Assakkaf, 2003, p.2-33).
They are mounted on two-axle carriers with cab of the operator that swings with the load sometimes mounted on the carrier. To improve maneuverability at the job site, they are fitted with large wheels. Although they can travel on highways, they are transported on low-bed trucks where long distances are involved since their maximum speed limit is 30 miles per hour. Most rough-terrain cranes have joysticks for controls. Common models are the 15-18 ton capacity range mainly used as utility machines used for lifting and capable of light intermittent duty-cycle jobs (Assakkaf, 2003, p.2-33).
All-terrain truck cranes
They are used for limited pick-and-carry work.They are dual cabbed cranes with the lower cab for use in fast highway travel and a superstructure cab which has the drive and crane controls. In cases where multiple lifts are required in scattered project sites or at multiple work locations on a single project, all-terrain truck cranes are ideal. However, its combination of two features makes it more costly than an equivalent capacity hydraulic or rough-terrain crane(Assakkaf, 2003, p.2-33).
Heavy lift cranes
They are machines where their lifting capacities is in the range of 600-2000 short-ton range. They consist of a boom and a counterweight each mounted on independent crawlers coupled by a stringer. To decrease compressive forces, the configuration utilizes a vertical strut and inclined mast (Assakkaf, 2003, p.2-33).
They take little space and provide high lifting weight with good radius. Three configurations exist for tower cranes. One configuration provides for a special vertical boom arrangement on a mobile crane. The second model provides for a mobile crane superstructure mounted on top of a tower and the third is where there is a vertical tower with a jib and operator’s cab at the top. While some towers are fixed with a swing circle mounted at the top, others are slewing types that have the swing circle located at the base and both the tower and the jib assembly rotate relative to the base. Tower cranes are usually recommended where state conditions are restrictive; where lift height and reach are extreme; and where there is zero mobility (Assakkaf, 2003, p.2-33).
The Aerial crane or ‘Sky cranes’ are the model of helicopters meant to lift large loads. They are applicable where it is hard to access since helicopters can travel to and lift in areas that conventional cranes cannot reach. Their most common usage is in lifting units/loads onto shopping malls and high-rises. They are able to lift many things using their lifting capacity, like cars, boats, and swimming pools. Adding to this, they carry out disaster relief after natural disasters for clean-up, and at times of wild-fires they carry huge buckets of water for fire extinguishing. Some aerial cranes have made used of lighter-than air aircraft, for example the aircraft. (Norman.Spencer, 2008-2012, p.4).
The Shipboard Aircraft Crash Handling and the Salvage Cranes for the US Navy is one type of crash crane used in aircraft carrier. It is designated CVCC for Carrier Vessel Crash Crane and AACC for Amphibious Assault Ship Crash Crane. They are self-propelled, six-wheeled and four-wheel drive, diesel-electric powered vehicles that mounted on pneumatic rubber tires. The cranes can operate aboard ship in the inclement weather. They are designed to be towed on the flight deck in an aircraft carrier or amphibious assault ship where they are exposed to extreme open-sea weather conditions and the corrosive effects of a salt water atmosphere. In service, the cranes will lift damaged aircraft (CVCC up to 75,000 lbs and AACC up to 70,000 lbs) from different locations and attitudes and carry loads on a rolling and pitching ship to a create parking zone on the flight deck (NAWCAD, 2011, p.1).
According to the US Department of Navy (2003) circular Carrier cranes for aircrafts and boats are designed with key performance parameters in mind. Of special focus are hoist and travel capability; hoist and slew capability; launch and recovery of ships’ boats and mean time between critical operational failures. In addition, the crane for aircraft carrier must meet military standards; meet other key requirements such as reliability and maintenance; incorporate safety features; electromagnetic compatibility; of appropriate design and construction; manufactured from recommended materials; workmanship; environmental requirements and quality assurance provisions (Naval Air Engineering Center,1985 ).
This chapter presents the methodology, which was used to carry out the study, the target population and sampling methods and the techniques, that was used to select the sample size. It also describes how data was collected and analysed.
Research design is the outline, plan or scheme that is used to generate answers to the research problem Kothari (200, p.315). It is basically the plan and structure of investigation. Descriptive research design will be used in the study. A questionnaire will be prepared to collect the relevant data and a statistical data analysis tool will be selected. Descriptive research seeks to establish factors associated with certain occurrences, outcomes, conditions or types of behavior. Descriptive research is a scientific method of investigation in which data is collected and analyzed in order to describe the current conditions, terms or relationships concerning a problem. This method will be preferred because it enables an in depth study of the phenomena. The research design is not only simple to but also convenient.
According to Kothari (2005, p.31) sampling is the process by which a relatively small number of individual, object or event is selected and analyzed in order to find out something about the entire population from which was selected. A sample is a small proportion of targeted population selected using some systematic form. The research used decisive sampling because it enabled generalization of a larger population with a margin of error that is statistically determinable.
Questionnaires will be used in this study. Questionnaires will be delivered using electronic means such as e-mails and collected after a few days. The types of questions used will be close- ended. Close-ended questions will be used to ensure that the given answers will be relevant. The research will phrase the questions clearly in order to make clear dimensions along which respondents answers would be analyzed. The presence of the researcher will not be required as the questionnaire will be self-administered.
Data Analysis Method
According to Kothari (2005, p.95), data analysis procedure includes the process of packaging the collected information putting in order and structuring its main components in a way that the findings can be easily and effectively communicated. After the fieldwork, before analysis, all questionnaires will be adequately checked for reliability and verification. Editing, coding and tabulation will be carried out in a systematic manner. The data will be analyzed using qualitative and quantitative techniques. Qualitative method involves content analysis and evaluation of text material. Quantitative method involves the use of tables and charts.
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