Rigid inflatable boats RIBs

Inflatable boats have been in use for many years and, with a small pay-load, can achieve high speed. The first rigid inflatables came into being in the 1960s with an inflatable tube surrounding a wooden hull. Much research has gone into developing very strong and durable fabrics for the tubes to enable them to withstand the harsh treatment these craft get. Later craft have used reinforced plastic and aluminium hulls. RIBs come in a wide range of sizes and types. Some are open, some have...

Acquiring Seakeeping Data

Computations of performance criteria require good data input, including that for waves, response operators and limitations experienced in ship operations. The sources of wave data have been discussed. The designer must select that data which is applicable to the design under review. The data can then be aggregated depending upon where in the world the ship is to operate and in which seasons of the year. Obtaining the response amplitude operators The designer can call upon theory, model testing...

Representing the hull form

The hull form is portrayed graphically by the lines plan or sheer plan (Figure 3.4). This shows the various curves of intersection between the hull and the three sets of orthogonal planes. Because the ship is symmetrical, by convention only one half is shown. The curves showing the intersections of the vertical fore and aft planes are grouped in the sheer profile the waterlines are grouped in the half breadth plan and the sections by transverse planes in the body plan. In merchant ships the...

Info

Made of the weight and centre of gravity position at the time of launch. To facilitate this a detailed record of all material built into the ship is kept, often backed up by actual weighing. In manual calculations the procedure adopted is to treat the launch as a quasi-static operation. That is it assumed that all forces and moments are in balance at every moment. A profile of the ship is moved progressively down a profile of the launch ways, taking account of the launching cradle. The moments...

Spreadsheets

It will be appreciated that the type of calculations discussed above lend themselves to the use of computer spreadsheets and Microsoft Excel is very convenient here as it is in many engineering situations as presented in Liengme (2002). A spreadsheet can be produced for the calculations in Table 4.1. This has been done to create Table 4.4. The first four columns present the ordinate number and the values of x, y and Simpson's multiplier. Assuming the x values are in cells B3 to B11, the y...

Appendix C Glossary of terms

In many cases the fuller definition of these terms, and the context in which they are used, will be found in the main text. They can be found by reference to the index. Where appropriate the usually accepted abbreviation is given. Terms shown in bold in the explanations are defined elsewhere in the glossary. Added mass. The effective increase in mass of a hull, due to the entrained water, when in motion. Added weight method. One method used in the calculation of a ship's damaged stability when...

Wind

Unfortunately for the ship designer and operator the air and the sea are seldom still. Strong winds can add to the resistance a ship experiences and make manoeuvring difficult. Beam winds will make a ship heel and winds create waves. The wave characteristics depend upon the wind's strength, the time for which it acts, its duration and the distance over which it acts, its fetch. The term sea is applied to waves generated locally by a wind. When waves have travelled out of the generation area...

Some General Design Attributes

It has been seen that a ship will need to possess certain characteristics, or attributes, to meet an owner's requirements. It is constructive to consider some general attributes of design which apply to all, or most, ship types. Different ship types are discussed in a later chapter. Usually there will be a certain volume of goods the ships of a fleet need to carry. This may have been established by a market survey. The 'goods' may be cargo, people or weaponry. How many ships are needed and the...

Multihulled vessels

These include sailing catamarans, trimarans, offshore rigs, diving support vessels and ferries. Catamarans are not new as two twin hulled paddle steamers of about 90 m length were built in the 1870s for cross channel service. They were liked by passengers for their seakeeping qualities but were overtaken fairly soon by other developments. The upper decks of catamarans provide large areas for passenger facilities in ferries or for helicopter operations. Their greater wetted hull surface area...

Directional Stability And Control

It was seen in an earlier chapter that when a ship, at rest in still, water is disturbed in the horizontal plane there are no hydrostatic forces to return it to its original position or to increase the movement. The ship is in neutral equilibrium. When a moving ship is disturbed in yaw it is acted upon by hydrodynamic forces which may be stabilizing or destabilizing. If stabilizing, the ship will take up a new steady line of advance but unless some corrective action is applied, by using the...

The impact of technology and computers

Over the last half-century technology has had a tremendous impact upon how ships are designed, built, operated and maintained. One could mention a myriad of examples but the following will serve as illustrations (1) Satellites in space have made it possible for ships to locate their position to within a few tens of metres using global positioning systems. The satellites can also pick up distress signals and locate the casualty for rescue organizations. They can measure sea conditions over wide...

Crude Oil Carriers

These carry the unrefined crude oil and they have significantly increased in size in order to obtain the economies of scale and to respond to the demands for more and more oil. Designations, such as Ultra Large Crude Carrier (ULCC) and Very Large Crude Carrier (VLCC), have been used for these huge vessels. The ULCC is a ship of 300 000 dwt or more the VLCC is 200 000-300 000 dwt. Crude oil tankers with deadweight tonnages in excess of half a million have been built although the current trend is...

Ship Handling

Several aspects of the handling of a ship are not brought out by the various manoeuvres discussed above. At low speed any hydrodynamic forces on the hull and rudders are small since they vary as the square of the speed. The master must use other means to manoeuvre the ship, including 1 Using one shaft, in a twin shaft ship, to go ahead while the other goes astern. 2 When leaving, or arriving at, the dockside a stern or head rope can be used as a pivot while going ahead or astern on the...

Full Scale Trials

The final test of the accuracy of any prediction method based on extrapolation from models must be the resistance of the ship itself. This cannot be found from speed trials although the overall accuracy of power estimation can be checked by them as will be explained in Chapter 10. In measuring a ship's resistance it is vital to ensure that the ship under test is running in open, smooth water. That is to say the method of towing or propelling it must not interfere with the flow of water around...

GZ curve See curve of statical stability

A term applied to bulk carriers of 40 000-65 000 DWT. Heave. The vertical movement of a ship, as a rigid body, in a seaway. Heel. The slow angular movement of a ship about a fore and aft axis. Angular movements as a result of waves are referred to as rolling. Hogging. A ship is said to hog when the hull is bent concave downwards by the forces acting on it. Hogging is the opposite of sagging. 418 APPENDIX C GLOSSARY OF TERMS Horizontal prismatic coefficient Cp . One of the...