Page 30: of Maritime Reporter Magazine (April 15, 1969)

LAD - A New Family Of Devices To Assist In Ship Conning Robert F. Riggs* Sperry Marine Systems Division has carried out extensive studies of ship conning functions for the Maritime Administration. Among other things, these studies included an analysis of the lookout's function in the conning of a vessel and a study of the feasibility of improving lookout efficiency with electro-mechanical aids. Hardware devices, called the lookout-assist-de-vice (LAD) were developed under this program to demonstrate the practical feasibility of auto-matically detecting vessels within set navigational ranges. Originally, the LAD concept was restricted to the function literally described by its name, but extensive studies have shown that there are many problems associated with the conning of a ship that can be more easily solved by proper sensors and displays. The word LAD has now come to connote a whole family of potential devices, sen-sors, and displays, of which the original lookout assist device is only a part. The studies demonstrated that a radar lookout-assist-device was theoretically feasible. This part of the LAD gear is called R-LAD. A feasibility demonstration of the equipment occurred at sea aboard the Humble Oil Company ship Esso Ban-gor during late 1965 and early 1966, with the result that feasibility of the R-LAD was proven to the satisfaction of both MarAd and ship oper-ating personnel. Further theoretical studies to consider feasibil-ity of a hearing lookout-assist-device (H-LAD) in the acoustic portion of LAD, were begun soon thereafter with the ultimate result that a feasibil-ity model of H-LAD has been constructed and is now undergoing trials aboard the Great Lakes bulk carrier Edward B. Greene of the Cleveland Cliffs Tron Company fleet. Results of the trials thus far have been largely satisfactory. The in-stallation aboard the Edward B. Greene combines both the radar and acoustic detection systems in a single system. Since detections with LAD use two sensing methods, radar and acoustic, the probability of detection will be greater than either one acting singly. Actually, a good deal of studs went into the choice of these two sensing techniques. Be-fore the choice, all known eligible sensing tech-niques. including radar, microwave radiometry, passive and active underwater sonar, laser radar, infrared, passive sound-in-air, and passive fog-horn listening were compared. The comparison involved sensor capabilities to search and detect an intruding merchant vessel within a reasonable time during unfavorable weather conditions. The sensor performance per dollar-of-cost became the sensor's figure-of-merit. The study showed that only passive foghorn listening and radar have acceptable figures-of-merit. Here we mean, of course, robot systems that automatically detect *Mr. Riggs, Sperry Marine Systems Division, Sperry Rand Corporation, presented the paper condensed here before the winter meeting of the Great Lakes and Great Rivers Section of The Society of Naval Architects and Marine Engineers. John L. Horton, assistant manager, Marine Department, The Cleve-land Cliffs Iron Company, presented a supplemen-tal paper reporting on the actual use of the LAD system. Figure 1?Experimental model of R-LAD showing how the guard-ring concept is incorporated in the bridge unit. other ships without the necessity for a human observer. '["lie concept of detection at a limited number of discrete ranges, as used with R-LAD, is called guard-ring detection. Figure 1 shows how the guard-ring concept has been incorporated into the exj>eriniental model of the R-LAD system. ()n the right of the figure is shown the display panel develo]>ed for the feasibility demonstration. Two dials rotate in synchronism with the R-LAD antenna. Each dial corresponds to a guard-ring. In this case there are two, an inner and an outer, which are usually set at approximately H/2 and 5 miles range, respectively. When a target crosses either guard ring, an alarm is sounded and the proper dial indicates bearing in relation to the intruder. In one mode, the dial can be made to stop altogether and the alarm made to continue until the conning officer resets the device. In another mode, the dial keeps rotating and an intermittent 'beep' and flashing light indicates that the intruder is still in the guard ring each time the R-LAD antenna scans past the target. In the combined If- and R-LAD system now undergoing trials aboard the Edward B. Greene, the R-LAD detections also initiate a recorded voice callout alarm which tells the conning officer in words that an object has been detected and in-dicates its bearing sector. A question often asked about R-LAD is. "What makes it so special?why can't any marine radar he modified to incorporate the guard-ring con-cept?" The answer is that R-LAD is required to fulfill several special requirements not normally adaptable to the usual marine radar design. In addition, the lookout can be considered as a sen-sor redundant to the ship's regular radar. In 11-LAD, the acoustic signals are picked up by a remote microphone array. The particular array being tested contains only three micro-phones -]x>rt. starboard, and aft. The array is about four feet in diameter and is enclosed in a teflon fabric windscreen. The windscreen has proven very effective; very little wind or rain noise has actually been ex|>erienced in the system. The electronic equipment is contained in the standard relay rack. The equipment consists of amplifiers, a recording system, audio-visual dis-plays. controls, an automatic alarm system, and a logic system for controlling the recorder. A simple block diagram of the entire H-Lad system is shown in Figure 2. Although at present only three receiving and amplifying channels are being used, the special amplifier system is capable of amplifying up to eight signals with equal gains and phase match over the band 100 to 4,000 Hz, the band of most interest to conning. Phase and gain balance allows faithful binaural reproduction of the signals to the observer's ears. This feature has been used iu one series of experiments to determine the bearing of sounds to within about 5 degrees ac-curacy. The amplified signals are also recorded with binaural fidelity and can be played back on command. Besides being recorded, the sounds picked up by the remote microphone array are continuously reproduced through a high fidelity speaker and stereo headset. Also, a visual display of the signals is available oil a cathode ray oscil-loscope that continuously indicates the bearings of all sound sources to about 45 degrees ac-curacy. Automatic alarms are given when a sound of sufficient amplitude and duration occurs in any RECEIVING ARR4V Figure 2?Block diagram of H-LAD system as currently being tested on the Edward B. Greene on the Great Lakes. one of the receiving channels. When this happens, appropriate alarms sound, warning lights are lit, and the recorded voice channel calls out the bear-ing to about 45 degrees accuracy. Coincidentally, the recorder system is made to store the sound that triggered the alarm. The storage time is ad-justable for a period of from zero to two minutes. If the recording is not played back within that time, the system automatically reverts to record mode. Results with this experimental version of LAD equipment have been encouraging. Detection prob-abilities of R-LAD have been about 97 percent against steel-lnilled vessels at six miles range. Compared to actual lookout performance, this is a considerable improvement and R-LAD works as well in bad as in good visibility. Acoustic reception by H-LAD has demonstrated about a one-mile increased detection range over the unaided lookout. The R-LAD and H-LAD sea trials have given Sperry Marine Systems Di-vision engineers valuable data necessary to de-sign a prototype version of LAD. Besides the new system, various other displays have been or are being considered that would permit the conning officer to formulate a safe and effective maneuver plan in a densely populated sea. without plotting or using a computer. The overall objectives are to improve safety, finesse in maneuvering, reliability, and to lower costs with-out compromising the conning officer's traditional role as the maker of decisions. 32 Maritime Reporter/Engineering News