bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vertical Sextants give Good Sights
Authors: Dixon Mark 
Published: November 2009

Many texts stress the need for marine sextants to be held precisely vertical at the instant that the altitude of a heavenly body is measured. Several authors lay particular emphasis on the technique of ‘rocking’ the instrument in a small arc about the horizontal axis to obtain a good sight. Nobody, to the author's knowledge, however, has attempted to quantify the errors involved, so as to compare them with other errors inherent in determining celestial position lines. This paper sets out to address these issues and to pose the question: what level of accuracy of vertical alignment can reasonably be expected during marine sextant work at sea ?When a heavenly body is brought to tangency with the visible horizon it is particularly important to ensure that the sextant is held in a truly vertical position. To this end the instrument is rocked gently about the horizontal so that the image of the body describes a small arc in the observer's field of vision. As Bruce Bauer points out, tangency with the horizon must be achieved during the process of rocking and not a second or so after rocking has been discontinued. The altitude is recorded for the instant that the body kisses the visible horizon at the lowest point of the rocking arc, as in Fig. 2. The only other visual clue as to whether the sextant is vertical is provided by the right angle made by the vertical edge of the horizon glass mirror with the horizon. There may also be some input from the observer's sense of balance and his hand orientation.
The Anderson Theorem
Authors: Anderson E. W. 
Published: November 2009

In 1835 Gustave-Gaspard Coriolis proved that, if a ‘body’ travelling unaccelerated at a speed v is made to conform to a medium rotating at a rate w, it will be accelerated sideways at vw. Hence air travelling freely, if subjected to the rotation of the Earth's surface, will be accelerated at – 2vω sin ø, –ω sin ø being the rate at which the local surface rotates, with –ω the speed at which the Earth spins and ø the local latitude. (In the diagrams ω is presented as Ω).2. Coriolis also proved the converse formula from which, if air travels freely over the surface of the Earth, it will accelerate at + 2ω sin ø relative to the local rotating surface. This reversed Coriolis formula happens to be far more important than the original direct formula. It has been applied to long-range artillery, to aircraft using spirit-level sextants, to inertial navigation systems and to the ground tracking of space craft. It has also been applied to forecasting wind speeds.3. We can handle the duality of Coriolis by a loop diagram as in Fig. 1. The central link shows the direct Coriolis acceleration produced when air travelling freely is forced to conform to the rotating surface of the Earth, The link to the left depicts the reversed Coriolis acceleration which applies to air travelling freely as seen from the local surface of the rotating Earth.
An Examination of Criticisms of Automatic Radar Plotting Systems and their Advantages in Relation to Manual and Semi-auto Systems
Authors: Herther J. C. , Wylie F. J. 
Published: November 2009

The remarks of Mr. Harrison under the above title demand some further comment. One can certainly agree with his substitution of ‘prediction’ for ‘plotting’ but not with his deletion of ‘supposed’. The latter begs the whole question whether the operator will be dangerously deceived and this is far from proven. The latter part of his second paragraph is a generality; there will be many combinations of range and speed in which the result will not be satisfactory.Mr. Harrison implies, although he does not come right out and say so, that errors arising during ‘classical’ manual plotting are ‘operationally’ acceptable while the errors in automatic plotting are unacceptable. Such a conclusion is illogical if one is willing to concede that any manual plotting procedure can be automated by the use of a digital computer. To examine this assertion in greater detail one may consider the automatic plotter to be made up of a data extraction section and a data processing section.
Plotter Display Philosophy
Authors: Rinaldi R. G. 
Published: November 2009

In Captain F. J. Wylie's article, ‘Maritime radar automatic plotter display philosophy’ in the July 1974 issue of the Journal, he states that the IBM Maritime Application Bridge System (MABS) tracks only six targets for collision assessment purposes. This statement is incomplete and I would like to clarify the impression left with your readers.The IBM MABS tracks up to 21 targets continuously while performing either automatic or manual acquisition. However, since the MABS also prioritizes targets according to threat potential (based on C.P.A. and T.C.P.A.), only the six most threatening are displayed continuously on the alpha-numeric data display and on the PPI. Should the operator wish to obtain data on the fifteen targets of lower priority he can request them in groups of six, in descending order.
VLCC Drift
Authors: Cumming J. A. 
Published: November 2009

There has recently been some discussion on the suspected ‘sailing effect’ experienced by ships lying immobilized in a seaway. It was suspected that drift direction may not be truly down-wind, and that on VLCCs in the ballasted condition the sailing effect could be magnified. Few practical data were however available and could easily be spoiled by the effects of current, or become unreliable if established under the influence of light to moderate winds.An unusual set of circumstances combined on the 3 August 1977 when I was Chief Officer of the Shell tanker SS Lima on her maiden voyage to the Persian Gulf. As can happen early in a ship's life, trouble developed in the engine room requiring the boiler to be shut down for about two days. The first signs of the problem were discovered a few days earlier but the stoppage was planned so that the ship would have plenty of sea room when undergoing repairs. A position off Maputo was chosen, and when within the selected area the ship was stopped and the repairs carried out. During this period the ship was allowed to drift freely and as usual daily positions were obtained at morning and evening twilight and at noon. Figure 1 is an outline chart of the area showing the observed positions. For these times the ship's head is also given, in addition to the associated wind direction and speed.
Crossing Traffic Separation Schemes
Authors: Richardson R. S. 
Published: November 2009

The provision of Rule 10 of the 1972 Collision Regulations, that if vessels are obliged to cross traffic lanes they shall do so as nearly as practicable at right angles to the general direction of traffic flow, would appear to be simple enough. Could it be however that in areas of high traffic density, such as the Dover Strait, the theoretical simplicity of the right-angle crossing introduces problems of its own?Crossing the Dover Strait several times a week, I am constantly alarmed by the apparent lack of regard for Rules 15 and 16 by vessels using the traffic scheme (The rules governing crossing situations and action required by the give-way vessel). I accept that some vessels using the lane believe, albeit incorrectly, that they have the right of way, but feel that a large proportion of these ‘port-side charlies’ are the result of the right-angle crossing.Because of the pattern of traffic the speed of crossing vessels in the Strait is generally considerably greater than that of vessels using the lanes. Under the present Regulations a situation frequently arises in which a vessel using the lane finds herself as the give-way vessel to another six points or more on her bow. An initial reluctance to alter course by this amount is followed by the thought that there is not sufficient sea-room in which to alter, and the give-way vessel stands on.
The Reduction of Astronomical Sights
Authors: Sadler D. H. 
Published: November 2009

The object of this paper is to describe, in principle, a method of reducing astronomical sights, of plotting the resulting position lines and of calculating a position from two or more sights. The method, which is thought to be new, requires neither a calculator nor extensive tables and appears to possess some advantages over more conventional methods. After a general description, and illustrations of two variations, the method is analysed in sufficient detail to indicate that its practical realization, to meet any specific requirement, is a straightforward matter of detailed design.No attempt is here made to translate the principles of the method into a form for practical use. The paper is mainly addressed to those interested in the theory of astronomical navigation; the description, together with the analysis and the illustrations, is available for use as a basis for a practical method of sight reduction – should anyone consider that there is a requirement! The treatment is intended to be rigorous, though much elementary mathematical detail has been omitted; in a practical application some care may be required near the singularities.
The ‘Manav’ Integrated Navigation System
Authors: Millar I. C. , Hansford R. F. 
Published: November 2009

The history of manav goes back fourteen years to 1967 when Esso placed a contract with the Ministry of Technology (mintech) to carry out work to develop a system to assist in ensuring the safe operation of its Very Large Crude Carriers, which were then coming into service. The 1967 era saw much public, governmental and company concern about the stopping and manoeuvring ability of large tankers, particularly when close to shore in estuaries or when berthing.manav was therefore one of a number of developments or studies initiated by the introduction of VLCCs. Some years were to pass before coordination of the various study results proved possible.The Racal-Decca (or Decca as it then was) involvement began in 1969 when Esso and mintech decided that an industrial partner should be sought. From the firms approached, the Decca Navigator Company was contracted to undertake a design study. The cost of this study, which started in January 1971, was equally shared between Decca and mintech. This said, it is remarkable how even with a wealth of supporting data having been collected in the intervening fourteen years, the objectives for manav, as set by Decca and mintech, have not radically changed.The present Department of Industry involvement in funding the sea trial evaluation of manav has its roots in yet a different study; namely the Bridge and Wheelhouse Ergonomics Study, which resulted in the DOI Code of Practice for Ship's Bridge Design.
The English Channel Passage Planning Guide
Authors: Halliwell H. R. W. 
Published: November 2009

The first edition of the English Channel Passage Planning Guide was published in February 1981, over a year ahead of the July 1982 routing changes, to familiarize navigators with this new type of publication and to gain experience from users. Edition 2 was published on 2 April 1982 to give advance warning of the full details of the new routing measures; it includes many suggestions from those who answered the questionnaire printed at intervals in Admiralty Notices to Mariners. Even before publication of Edition 1 we had had much useful advice from various professional bodies and, throughout, we have tried to meet the known wishes of those who would be using the Guide.Format is not the most important feature but it is one on which strong views were expressed. Edition 1 was plainly over-large and unwieldy. We have now reduced the width to standard chart size and completely redesigned the panels to permit folding to a size of about 10 × 14 inches. This compromise between chart and booklet should combine the virtues of a chart (quick correction and filing with other charts where its existence will not be overlooked) and some of the virtues of a booklet (folded, it will not cover the whole of a standard chart which may be in use at the same time).
The Still Undiscovered Origin of Portolan Charts
Authors: Freiesleben H. C. 
Published: November 2009

The term ‘portolan chart’ first occurs in Italy in the thirteenth century, not long after this aid to navigation came into general use on board ship. The Italian word portolano, however, can best be translated as ‘pilot book’ or ‘sailing directions’, a different aid to navigation of which one example survives from the fourth century b.c., and pilot books are indeed still published in modern form by all seafaring nations. References by Herodotus in the History make it probable that such documents already existed in his time, and under the name of periplus they continued up to the sixth century a.d.; after which they do not appear again until the golden age of navigation in Italy and Catalonia in the late Middle Ages, apart from some much simpler early medieval types. The portolano or periplus is a description of ports, with information required by the navigator concerning anchorages, dangers threatening landfall and the winds and weather over wider areas. Commercial information was sometimes included, obviously also a matter of interest to the mariner who could read, though it may be doubted if many of them then could.Italian portolan charts exist from almost the same period as the portolani, both of them denoted by the same word compasso, but while the pilot books have their modern successors the charts were only produced up to the beginning of the seventeenth century and are not really the forerunners of the modern sea chart.
How Children Navigate
Authors: Spencer Christopher , Blades Mark 
Published: November 2009

The paper by Spencer and Blades, both of the Department of Psychology in the University of Sheffield, was presented on 14 March 1984 at an Institute meeting held in London to discuss Psychology and Navigation.From its earliest moments, the young organism has a need to track and integrate into some scheme of knowledge the location of salient objects and places; and thence to develop navigational strategies for efficient movement through space. In the case of human young, their initially limited mobility constrains the extent of their active explorations, and thus their range of experience; and adult protectiveness (somewhat heightened in the modern, suburban nuclear family setting) continues to limit such explorations even when the child is fully capable of extensive movement round the local area (Pick and Acredolo, 1983).
The Effects of Sonic Boom on the Ecological Environment
Authors: Cerri C. 
Published: November 2009

It is expected that the number of military and civil aircraft operating supersonically all over the world may remain the same during the next decade. The problem of sonic boom, which has been by-passed for military aircraft through the assignment of specially allocated ranges for supersonic operation, is still with us and is likely to influence the operation of supersonic transport (SST) aircraft, the Concorde and the Tupolev 144. Concorde is still short of reaching the break-even point, despite the large traffic gain registered on the routes to North and South America. The problem is to get overland routes; the difficulties encountered by the UK in the discussions with India and Malaysia for the establishment of a London–Bahrain–Singapore route are well known.Before presenting the effects of the sonic boom on the ecology it may be well to summarize the nature and the main features of this phenomenon.(i) The N-wave signature. A complex body like an aircraft, moving in supersonic flight, generates a pattern of local shock waves which tend to coalesce in two main shock cones, the front (or bow) and tail, as the distance from the aircraft increases. A shock wave is a discontinuity surface for the thermodynamic characteristics of the fluid, the most important being the static pressure jump responsible for the N-shaped pressure signature characteristic of the sonic boom. Other parameters are of minor importance to the environment. A shock signature is denned by the following parameters:
Development of Routing in Coastal Waters
Authors: Cockcroft A. N. 
Published: November 2009

Traffic separation schemes and other routing measures have now been established in the coastal waters of many countries and new schemes are being introduced each year. Traffic separation was originally intended to reduce the risk of collision between ships proceeding in opposite directions but this paper explains how routing measures are now being used mainly for coastal protection. Improvements in navigational aids may lead to more extensive routing schemes in the future with increasing restriction on the movement of shipping.The first traffic separation schemes adopted by IMCO (now IMO) in 1965 and 1968 were based on proposals made by the Institutes of Navigation of France, the Federal German Republic and the United Kingdom. In the report submitted to the Organisation by the Institutes in 1964 it was stated that ‘the object of any form of routing is to ease the congestion and lessen the likelihood of end-on encounters by separating opposing streams of traffic …’.
The Estimation of Losses Resulting from Marine Accidents
Authors: Fujii Yahei 
Published: November 2009

Studies have already been published on the probability of collision at sea, the effect of darkness and reduced visibility on the probability of collision, and on the distribution of collisions in particular areas. Only Minorsky and Comstock appear to have studied the extent of the resulting damage and sufficient data are not available for detailed analysis.The establishment and operation of any traffic management system calls for a considerable outlay, so that an objective estimate of the extent of collision losses is often required. Such a cost/benefit survey was carried out by the Japan Transport Economics Research Centre on the assumption that a traffic management system can greatly reduce the incidence of collisions involving vessels of over 3000 g.r.t. Since half the aggregate loss is shown to relate to these large vessels (and considering their increasing capital value), an expenditure of ten billion yen or more (£20 million) over a period of ten years would appear to be cost effective if its primary purpose were to avert accidents to large vessels.
A New Navigation Computer
Authors: Richey Michael 
Published: November 2009

Through the mediacy of Professor Torao Mozai and the courtesy of Captain T. Iimura of Omron Tateisi Electronics, Tokyo, I was lent a prototype Omron lop NC Astro-navigation computer to evaluate during the course of a singlehanded race in Jester from Newport, Rhode Island, to Bermuda and the subsequent voyage back to England. Although it has been developed as an all-purpose navigation computer, the particular requirements of single-handed oceanic navigation might, it was thought, provide a useful commentary on this kind of instrument; and the environment of a small boat, so close to the sea surface and inevitably inimical to electronic equipment, would be an austere test of the instrument's seaworthiness.This note is intended for navigators and so far as possible computer terms will be avoided. (The instrument is named a computer by its makers and will be referred to as such, rather than as a calculator, throughout.) The computer weighs 2·5 kg. and measures 200 × 289 × 91 mm. It operates from either the mains or batteries, and can be used for 10 hours continuously without a battery recharge.
The Dover Strait Information Service: Recent Progress
Authors: Emden R. K. 
Published: November 2009

This paper, which was presented at a meeting of the Merseyside Branch of the Institute on 24 February 1976, is a sequel to Captain Emden's paper on the setting up of the Dover Strait Information Service which was published in the April 1975 issue of this Journal.It will be recalled that in 1971 the Marine Division of the Department of Trade set in motion a number of activities designed to improve the safety of navigation in the Dover Strait. It is convenient to group these activities under three headings: scientific studies of marine traffic, surveillance and the Information Service, and future developments. It is the purpose of this paper to give an up-to-date report on each of these subjects.
Concorde Navigation
Authors: Calvert B. J. , Guest T. C. R. 
Published: November 2009

This account of the practical steps taken by British Airways to provide the Concorde with a reliable navigation capability which meets the needs of supersonic flight on commercial routes covers: the features of supersonic flight which lead to new navigation requirements, the social and political constraints on supersonic flight, and the need for the crew both to be well informed of the progress of the flight and prepared for the possibility of return to subsonic flight. These factors have led to special techniques for route planning, flight planning, documentation (including charts), and accuracy of navigation.All these techniques are based on a navigation system constructed from standard components, but meeting the aircraft's needs for accuracy and automation.
Sources of Latitude Error in English Sixteenth Century Navigation
Authors: Forty Gerald 
Published: November 2009

An examination of accounts of sixteenth-century voyages shows that the estimations of latitude then arrived at by astronomical means were subject to widely varying error. The purpose of the present study has been to discover by practical experiments at sea, with replicas of instruments in use at the time, to what extent the size and irregularity of the errors can be attributed to the characteristics of the instruments and to what extent they arise from other causes. Observations were made from a 9-ton yacht under conditions not wholly dissimilar to those obtaining in some of the very small ships whose voyages are recorded.The evidence for latitude errors is derived from published studies and from the writer's own analyses of three voyages made in northern waters by ships of the Muscovy Company: those of Stephen Borough of 1556 and 1557 and that of Arthur Pet and Charles Jackman of 1580. These were chosen because the masters in that Company's service received the best nagivational advice of the time3 and from the early 1550s onwards regularly recorded both latitude and compass variation. Furthermore, the relatively low altitude of the Sun in the higher latitudes was conducive to greater accuracy with a cross-staff.