Restricted Visibility Research Articles

Calculation of the Geometry of Ship Collision Zones

An account of the calculation of the geometry of collision zones surrounding vessels engaged in overtaking and meeting encounters is given. The zones are calculated for a range of mariners' decision times corresponding to clear and restricted visibility. The determination of encounter risk from the size of the zones is discussed.

The Calculation of Crossing Collisoion Risk at Sea

Mean relative collision risks for marine crossing encounters are derived from calculated encounter rates by the use of a two-part weighting function. The relative importance of the two parts is determined from data concerning the collisions which have taken place during the last few years. The method is applied to the crossing traffic in the English Channel to obtain the optimum crossing angles in both clear and restricted visibility.

Habitat, Group Size, and the Behaviour of White-Tailed Deer

AbstractThe behaviour of white-tailed deer on Ossabaw Island, Georgia was examined in three habitats which differed in cover density and forage abundance. Forest had relatively dense cover but low forage availability; wooded pasture had relatively dense cover and abundant forage; open pasture had no woody cover but abundant forage. Deer groups were small in both the forest and the wooded pasture relative to groups in the open pasture. Group size in the open pasture did not vary with seasonal changes in forage supply. Groups were small in open pasture during the autumn rut when food was abundant, but were relatively large at other times of year, even during the winter when forage abundance was comparable to that in the forest. Deer in the open pasture spent more time feeding, less time moving, and less time alert than did deer in the forest. Deer in the wooded pasture were intermediate between deer in the other two habitats for percent time feeding, more similar to deer in the open pasture for percent time moving, and more like deer in the forest for percent time alert. Differences in alert behaviour suggest that deer in dense vegetation (e.g. forest and wooded pasture) were more wary than deer in open areas. In all habitats, deer in larger groups (four or more deer) spent more time feeding and less time alert than deer in smaller groups. More aggressive interactions were seen in the open pasture; more nonaggressive interactions were seen in the forest. The rate of aggressive interaction was not clearly related to group size. Temporal variation in nearest-neighbor distance within groups was greater in the forest than in the open pasture, possibly due to loss of contact between deer under conditions of restricted visibility. Although these data suggest that cover density rather than forage characteristics was related to deer group size, no support was given for the hypothesis that this relationship was a consequence of different anti-predator strategies. Groups may have been smaller in dense vegetation because deer had difficulty maintaining contact with other group members when visibility was restricted.

視界制限状態における情報の性質と航法についての考察

In restricted visibility, information concerning another vessels will be scanty. So, it is more difficult to expect effective action to avoid collision than in sight of one another. Although 1972 Regulation rules conduct of vessels in restricted visibility, it is always depending upon a correct judgement of navigation officers by radar and sound signal information. In this paper, author considered characteristics of information and conduct of vessels in restricted visibility, and investigated actual cases of ship's collision. Finding are as follows. (1) Number of cases of ship's collision is not decreased. (2) Radar look-out is not appropriate. (3) Vessels do not proceed at a safe speed. (4) Action taken to avoid collision is not sufficiently put into practice according to regulation. (5) Proper use is not made in radar observation.

Sailing Problems Within and Near Traffic Separation Schemes

Traffic separation schemes have been established all over the world with the aim of reducing the danger of collision. Field observations have shown that despite the adoption by IMO and the laying down of the schemes on nautical charts a good many vessels do not comply with the steering and sailing rules applicable at traffic separation schemes. This paper attempts to review the apparent difficulties met. Some suggestions for improving of the situation are made.The separation of traffic into two streams moving in opposite directions has been introduced with the aim of reducing the incidence of collisions. Such a measure results in a decrease of the rate of encounters and an almost total elimination of head-on or fine crossing meetings which are considered dangerous especially in restricted visibility. Investigations have confirmed the effectiveness of the measure in achieving the purpose provided that the steps taken are reasonable from a practical point of view.

関門海峡における風速・視程の出現頻度および衝突海難に及ぼす影響

The sea collision generally occurs as the results of complicated interaction of the natural and human factors, the representatives of the former being the topography, oceanographic and meteorological conditions, and those of the latter being the conditions of navigators in connection with the ship's performance. The collision in the Kanmon Strait apt to occur under strong wind and restricted visibility. For the purpose of safety traffic management, it is necessary to represent numerically the actual states of wind, visibility, and their relation to the frequency of sea collision therein, for only insufficient information were avairable in spite of the cardinal importance of this strait for marine traffic. In the present report, the following two formulae for evaluating the frequency of sea collision in the Kanmon Strait under respective conditions were proposed, basing on the fomulae showing the distribution of wind velocity and visibility estimated from the records offered by maritime and meteorological authorities concerned. 1) For wind velocity pc[V_W]=sin^2{3.38-2.19√<V_W+1>+0.04(V_W+1)} where pc[V_W] =collision probability in the wind velocity V_w=wind velocity in meter per second 2) For visibility pc[D_V]=sin^2(1.31<D_V>^<-0.30>) where pc[D_V]=collision probability in the visible distance D_V=visible distance in kilometer

Collision Avoidance Manoeuvres in Restricted Visibility

Circumstances of collision. Over a fourteen-year period more than 80 per cent of all collisions in the Dover Strait occurred in reduced visibility. The majority of the ships concerned were carrying radar, so a possible inference is that the information available from this source is less effective than direct vision in successfully resolving close-quarters situations. The introduction of the Imco recommended routing scheme, the support measures mounted from the two sides of the Channel and sustained improvements in navigation have together led to a significant reduction in the number of collisions in poor visibility. However the risks, though reduced, remain higher than in good visibility.The circumstances leading to collision are very rarely known reliably or in any detail, but such facts as are known can be helpful if treated with caution. Reference 1 gives details of manoeuvres preceding 47 collisions, nearly all in fog, where helm orders were noted in crew reports (Table 1). About three-quarters of these collisions (and of collisions as a whole) occurred when ships were on opposing courses, as defined by their ports of call.

I—A Mariner' View

In clear-weather conditions well trained mariners experience little difficulty in dealing with multi-ship encounters in all circumstances. In restricted visibility they do not display the same confidence in manœuvring even in the open sea, and the problem is amplified as the waters narrow and the traffic density increases. The plea of the mariner would be to find an anti-collision system that would make manœuvring in fog at least as straightforward as in clear weather. To satisfy such a request it might seem that there would need to be two systems, one for fog and another for clear, but it seems probable that a system evolved to work safely in fog would also be acceptable in the less demanding conditions of clear weather; this would in time be the only system adopted.

海上衝突予防法の視界外適用航法について

海上衝突予防法の視界外適用航法について

Visibility Changes in Ohio, Kentucky, and Tennessee From 1962 to 1969

Abstract Previous studies of changes in visibility over a period of years have indicated either a general trend toward better horizontal visibilities or no change. In this study, visibility, relative humidity, wind direction, and other related data from three National Weather Service Offices (Akron, Ohio; Lexington, Ky.; Memphis, Tenn.) are used to determine changes in daylight visibilities during the summer seasons of 1962–69. Analyses of the data indicate that the percent of restricted visibility was greater during the period 1966–69 than during the period 1962–65 both before and after adjustment for the effects of location, time of day, humidity, and wind.

A System of Rules for Preventing Collisions at Sea

The following proposed system of rules was presented to the Collision Regulations Working Party of the Institute by Admiral García-Frías and is referred to in the January issue of the Journal (24, 56–9).IT is evident that the revision of the Collision Regulations would only be effective with a system of Rules able to cope with all situations that may arise at sea. The system must include all that it is necessary and sufficient to solve the collision problem in the easiest and most effective way and consequently it must apply both in clear weather and in restricted visibility using radar; differences between these situations being defined, if necessary, in every Rule.

Practical Manœuvres to Avoid Collision at Sea

The problem of avoiding collisions at sea, particularly in restricted visibility, is not likely to have one simple solution. Indeed there are three main areas which need separate consideration because of their different requirements. First, in rivers and estuaries, port approaches and narrow passages traffic is rigidly confined. Second, in waters adjacent to coastlines and in some other areas dense traffic has limited space in which to manœuvre. Third, in the open sea there are fewer encounters and unlimited manœuvring space. It seems probable that the best solution to the first of these problems will be found in shore surveillance of the traffic and regulation of the traffic flow by a licensed authority. Prescribed routes with perhaps speed limits and policing may solve the second, but only ratification of an internationally accepted rule of behaviour will satisfy the third requirement. This paper proposes to develop a set of manœuvres which may be applied as a rule which will be accepted as a possible solution to the third requirement.

Cooling Tower Fog: Control and Abatement

Fogs from cooling towers are causing an increasing number of visibility problems in addition to icing of roads, sidewalks, powerlines, etc. during freezing weather. Enforcement of regulations on thermal pollution for water quality control will cause an increase in the number of cooling towers, spray ponds, etc. Violations of visibility obstruction will rise unless the problems associated with winter operation of low-grade waste heat disposal systems are incorporated in design criteria. This paper summarizes a study made to ascertain the best method of fog control or abatement at a refinery in Houston, Texas. The induced draft, counter-flow cooling towers of concern have design capacities of 750 × 106 Btu/hr and 225 × 106 Btu/hr under local climatic conditions. Several methods of alleviating restricted visibility were considered and cost estimates were made for the most promising methods. A summary of these is provided in the text.

Reproductive Success and Age Distribution of Black Brant

Reproductive Success and Age Distribution of Black Brant

The Revision of the Rules

If the present Collision Regulations are defective, it is largely because the principles underlying them are not sufficiently developed for today's circumstances. In this paper Admiral García-Frías of the Spanish Navy attempts such a development and proposes a new set of rules, adapted to present circumstances, for vessels in sight of one another. These proposals, with the set of rules previously suggested in this Journal for restricted visibility using radar, form a complete system for avoiding collisions in both situations so that it would be easy to pass safely from one situation to the other when necessary, because of the unity of principles they present.It is encouraging for certain schools of thought—which started some years ago advocating the revision of the Collision Regulations for occasions when radar was being used in restricted visibility—that there now seems to be a general dissatisfaction amongst seafarers with the lack of guidance provided in the rules. Consequently, they are at last interested in a fundamental review of the Regulations.

霧堤付近の行動等(日本航海学会第43回講演会)

Making an attempt to show a concrete guide to practical affairs, signal and conduct of a vessel in the neighbourhood of a fog bank were considered. In this paper were shown chiefly the cases for restricted visibility in the neighbourhood of a fog bank to correspond to the fact of restricted one in Regulations and the points for signal and conduct of a vessel under actual circumstances and conditions to shift to lawful ones in Part C of Regulations.

Collision Avoidance in Restricted Visibility

In the January 1966 edition of this Journal Captain Wylie has given a lucid summary of the factors involved in the presentation on radar displays of true and relative motion. He also stated a conclusion on the combinations of display and ancillary equipment which he considers best satisfy the requirements for use when plotting to avoid collision at sea. Whilst acknowledging with respect all the work he has done to clarify the issues raised on this important but contentious subject over a number of years, a number of us has found it impossible to agree with his latest findings. As these may influence opinion in the shipping industry, the Board of Trade, the Courts of Law and the radar manufacturing industry, both at official and unofficial levels, they should not go unchallenged. Our disagreement concerns the priorities defined for display equipment and the method to be used for plotting. There can be no disagreement on academic principles.

レーダ航法における大角度変針について船用レーダシミュレータ実験による一考察(日本航海学会第34回講演会)

When a vessel is navigating with the aid of radar in restricted visibility, it is recommended that the alteration of course angle be substantially increased in order to prevent collisions. The substantial action is recommended not only because this would probably have the greatest effect, but also because it would be more likely to be noticed on the radar screen of the other vessel. As regards alteration in course angle, it is recommeded that a minimum alteration of 60 degrees be the standard navigational practice. However, the purpose of this recommended angle is not generally known to and understood by many navigators. In the study of the problem in question, the authors have made some studies and conducted some experiments with the use of the Marine Radar Simulator. As the result of these actions, one of the most important experimental studies was the study to determine the observer's notice of target's motion change which arises from the different angle of course alteration. We, therefore, advocate the results of experimental studies in substantial action which can make effective pictures on the radar screen to the navigators who are continuously watching it.

The Design of Ships' Bridges

The following discussion on the design of ships' bridges took place at a technical session of the Institute held in London on 6 January 1965. Captain Wacher illustrated the layout he proposed with a diagram.Captain J. F. Wacher, P. &amp; O.—Orient Lines. Existing general arrangements of the bridge, wheelhouse and chart room are inadequate for the needs of fast modern ships; the disposition of navigation, control, communication and safety instrumentation also leaves much to be desired. In recent years this has been recognized, prompted by an alarming increase in the number of ship collisions, particularly those which have occurred in restricted visibility.

Shore Radar Control in the Port Entrance Area

The paper discusses the measure of control to be exercised by the Port Authority in a Port Entrance Area where shore radar enables tracks to be made of all ships present. The problem becomes acute where great numbers of ships are trying to enter and leave in restricted visibility, creating danger and confusion.In a previous paper presented at the conference, Commandant R. Betton, Captain of the Port of Le Havre, suggested that it was perfectly possible for shore-based guidance radars to be used to reduce collision risks at the entrances to harbours, provided this supplementary function is precisely denned in terms of how much authority harbour administrations can exercise over ships outside the harbour. Betton stipulated that any control should only be exercised by experienced seamen and that they should not have the right to interfere in manœuvres for which masters should have sole responsibility.