GB2147168A - Anti-collision radar plotting aid - Google Patents

Abstract

A radar display in the form of a transparent LCD (14) is overlaid on a navigation chart (13a) so that a navigator can see target and track information obtained by a marine radar (11) in direct relation to the information on the chart, whereby to assist him in determining the best course for his vessel; for instance, the chart No. may indicate that a shipping lane alters course, and so that a ship on a potential collision course can be expected to change course, and so no evasive action is necessary. Hazards (such as shallow water) may also be shown. <IMAGE>

Description

SPECIFICATION Anti-collision radar plotting aids This invention relates to marine radar and in particularto anti-collision radar plotting aids (ARPA).

According to the present invention, there is pro videdan anti-collision radar plotting aid for use with marine radar, comprising a transparent display for superposition on a navigation chart, meansforstoring target and track information determined bythe marine radararidcausing said information to be indicated on the transparent display, whereby a navigator can view the targetand track information in direct relation to the information on the navigation chart.

Embodiments ofthe present invention will now be described with reference to the accompanying draw ings, in wh: Fig. -1 illustrates a true motion radar plot of a three ship situation, Fig. Zillustratesthe radar plot of Fig. 1 superim posed on the corresponding navigational chart; Fig. 3 illústratesatrue motion radar plot of another three ship situation;; Fig. 4 illustrates the radar plot of Fig. 3 superim posed on the corresponding navigational chart, and Fig. 5 illustrates schematically an arrangement of radar display overlaidonachart In December 1976the Liberian registered tanker "Argo Merchant" ran around on the Nantucket Shoals producing a large. ail slickwhich broughtthe threat of oil pollution to the coast of Massachusetts. This resulted in political pressure in the United States of America for action to reduce similar accidents.It was subsequently announcedthat a series of regulations would be drawn up concerning electronic equipment requirements and by 1;stSanuary, 1984 vessels of certain types andsizeswill be required to carry ARPA equipment iftheyaretotradewith the United States of America.

Considerableanxiety has been expressed by the Navigationicommunaywhich feels thatthe required sophisticattid:aids hidethe basic limitations inherent in radar and that accident reduction may well not take place unibsstheselimitations are understood by the navigator, andthey aretaken fully acount of in the navigation.

The anti-catlision task involves both equipment and personnel. Radar on one vessel is employed to determine range and bearing to targets (including othervessels) existing at the present moment. When used in conjunction with a store, forexample a CRT with long persistence, a pictorial presentation of past vessel tracks is given. A computer can be employed to enable forward extrapolation of vessel tracks and it can examine the consequence of various avoidance manoeuvres.Atthis point the navigator of the one vessel Enust evaluate these consequences, taking into accourZrit his estimate ofwhatthe other vessels are likelyao do. In the process ofthis he will seekto establish bridge to bridge communication with the other vessels to discuss with them a process which will ensu re safety for all vessels concerned, The chosen manoeuvre can then be executed.

This process of providing optimum safety is hindered by three fundamental obstacles. Firstly, any extrapolation forward relating to another vessel's track (prediction) assumesthatitwill continue on its present heading fortheforeseeablefuture. This is frequently an invalid assumption since if that vessel can see a danger it will endeavourto avoid the danger.

It will thus change its heading and possibily do so in a way which coupled with changes envisaged on the one vessel increases the danger of collision rather than reducing it. Secondly, before the one vessel decides what to do it is desirable to exchange information by voice communication with the other vessels to discuss various manoeuvres. There is, however, no information available from the radar as to the identity of the other vessels. This makes bridge to bridge VHF communication difficult. Thirdly, ships velocity sensors tend to be unreliable at slow speed, and there is sometimes confusion aboutwhetherthe ship's speed is relative to the seabed or relative to water mass.

A practical prediction problem will now be describedwith referenceto Fig. 1 which shows atrue motion radar plot of a three ship situation in St.

George's Channel offthe Irish Coast 4. One track indicates the position, and the direction is indicated by an arrow, of one vessel 1 ("ourvessel")whilstthe other two tracks indicate the positions of two other vessels 2 and 3 moving in nearlythe opposite direction. Our vessel 1 might find it tempting to turn starboard to avoid vessel 2, butthis could increase the danger with respectto vessel 3. From this radar plot there is no further information astowhateithervessel 2 or3 might do.While a good navigator will tryto manually transfer radar information to a chart, it is difficult to do so for manytargets. In any case, chart and radar may not be close together on the ship's bridge and the ambient illumination required for radar and chart may be sufficiently different to make such transfers difficult on a regular basis.

If, however, the radar information is superimposed on the relevant chart as shown schematically in Fig. 2, for clarity some of the chart information has been omitted, then it can be seen that vessel 2 which appears two present danger is moving generally south in a one-way lane and will shortly come to a bend Sin the one-way structure and can then be expected to turn starboard. Vessel 1 should, therefore, notturn until it knows whether in fact vessel 2 does as expected. This would be the safest and collision will then be avoided with both vessels 2 and 3.

Fig. 3 shows another true motion radar situation of three vessels in the Dover Strait, 6 indicating Dover Harbour wall. To "our" vessel 7 which is proceeding south-westerly, vessel 8 represents a threat. It might be tempting for vessel 7 to turn starboard to avoid vessel 8, but that could increase the risk of a close encounter with vessel 9. Superimposing the radar information on the corresponding chart as in Fig. 4 shows that vessel 8 is, however, close to the traffic lane 10 boundary. In orderto adhere to the general rules of navigation vessel 8 will, therefore, shortly have to altercourseto starboard in orderto cross the traffic lane at near 900.

Athird example of course prediction is concerned with sub-sea level features. The radar shows only what is above sea level whereas a chart shows what is below. Thus the radar plot superimposed on a chart gives clues as to what anothervessel may do if it is aware of dangerous features ahead, such as effecting a turn to steer awayfrom a shallow sandbank.

The above three examples showthat if the track of othervessels is shown on a chart then on can predict with a reasonable probability of being correct what another vessel will do, before it does so. This is significantly betterthan relying on the radar which can only indicatewhatthevessel will do assuming no course changes are made. As mentioned above a good navigator will tryto manuallytransferthe radar information to a chart, however, this is not easy. Fig. 5 illustrates, schematicaly, an arrangement whereby the radar information is automaticallu displayed relative to (overlaid on) a chart. A conventional marine radar equipment 11 isconnectedtocontrol unit 12 which is mounted nearto astandard charttable 13.

The control unit 12 is connected to a liquid crystal display 14which is transparent. This display may be of rectangularshape with dimensions equal to a proportion of the chart 13a. The control unit includes a store which is under microprocessor control. The store has a record of positions and velocity oftargets being tracked and these are displayed on the display 14.

Thustheliquidcrystal display 14holds information extracted from the radar in a plan position indicator form and my be considered as a remote radar display.

The control unit includes a keyboard which enables the navigator to input chart scale, orientation and starting position such that a track of "our" vessel, that is the one being navigated, will move on the display with a speed corresponding to chart scale and such that the other vessels will move correspondingly.

Claims (4)

1. An anti-collision radar plotting aid for use with marine radar, comprising a transparent display for superposition on a navigation chart, meansforstoring target and track information determined by the marine radar and causing said information to be indicated on the transparent display, whereby a navigator can view the target and track information in direct relation to the information on the navigation chart.

2. An aid as claimed in claim 1, wherein the display comprises a liquid crystal display.

3. An aid as claimed in claim 1 or claim 2, including meanswherebythe navigator can input chart scale, orientation and starting position whereby the vessel which the navigator is navigating appears on the displaywith a speed corresponding to chart scale.

4. An anti-collision radar plotting aid substantially as herein described with reference to the accompanying drawings.