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EVALUATION OF ME SAFETY OF SHI P NAVIGATION IN HARBORS Donald A. Atkins William R. Bertsabe* Abstract Concern for safety of navigation in harbor waterways teas increased due to the huge economic and environmental consequences of potential accidents to those ships of rapidly escalating size operated or proposed for operation in harbors today. The authors describe a methodology for the determination of ship and waterway navigational safety, including the definition of measurement indices of safe navigation and the means for determining their values. This methodology is the result of extensive research sponsored by the Maritime Administration and the U.S. Coast Guard involving the study of navigation of ships in harbor waterways through real-time simulators. Ship operators, port authorities, and regulatory agencies can apply the methodology to establish port and waterway designs or to evaluate the safety of accommodating potential traffic. The methodology is applicable to evaluation of limiting environmental conditions (i.e., visibility, wind, current) beyond which piloting of certain ship types can be considered unsafe, and examination of the effects of alternative aids to navigation, redesign of channels and turns, new traffic policies, or less-maneuverable ships. Specific applications of the methodology and measures of safety to changes in ship controllability, turn design, and aids to navigation are included. An analysis of the channel characteristics of 32 U.S. harbors {i.e., channel widths, depths, turn angles, turn types) is included to serve as reference material for future U.S. ship designs. Introduction The advent of large ships carrying cargo harmful to the environment and the economic advantage of accommodating oversized vessels in existing ports has focused the attention of the public, port _. ~ ~ _ ~ agencies on the need for improvements in the safety of navigation in U.S. port waterways. To date, navigational safety in U.S. port waterways has been maintained at au~norleles, sole operators . and government *Presenter. 53

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54 a relatively high level by virtue of an evolutionary process. Ship size increased at a slow enough pace that channel requirements, aid to navigation requirements, and ship maneuverability requirements could be determined by trial and error. Given a number of near misses and an occasional accident, port and ship designs were improved to acceptable levels of safety. As one port showed its capability to accommodate particular vessels, another port sought the same type of traffic by improving its own design to be equivalent to the first. Out of this experience and limited research, rules of thumb and empirically derived design criteria evolved for channel dimensions, aids to navigation, and ship design. Our difficulty today arises from the rapid escalation in ship size and the potential outdating of the available design criteria. An analysis of shipping traffic in U.S. port waterways would show that by many existing design policies and standards, present waterways cannot safely accommodate many of the large ships using the waterway today, much less the larger vessels of the future. Are present operations of oversized vessels safe or are we in a time-bomb situation? What is the present margin of safety for navigating large ships in existing channels? What economical improvements can be made to increase the margin of safety? Clearly, analytical techniques need to be developed for quantitative evaluation of the navigational safety of narrow waterways for large ships. The evolutionary process is too slow to provide the criteria in a timely fashion and the environmental, economic, and social consequences of a major marine accident are too high to risk. Statement of the Problem Research conducted in the area of navigation of ships in narrow waterways was for many years focused on hydraulic channel testing and simulation of ships' hydrodynamic response in analog or digital computer models. These methods were used to evaluate a single transit of a channel by a ship. Typically, autopilot rudder and propulsion control algorithms were used to control the model or the simulation. The advantages of such research methods were repeatability, and the ability to isolate and study unique hydrodynamic responses. These research methods provided valuable data about the vessel's physical response in the waterway. The extent to which these vessels could safely transit the waterway, however, could not be ascertained, since theme methods failed to acount for the variability the pilot and helmsman introduce. Recognizing this deficiency during the past decade, several research institutions around the world have integrated the human element into research through the use of ship simulators. By considering the variability man's performance adds to the piloting process, we are truly considering the ultimate safety of the vessel in the waterway, for a waterway can be said to be safe to the extent that variability of ship tracks in the waterway can be contained within the boundaries of the waterway under stated environmental conditions.

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55 The variability under study is that normally resulting from differences in perceptual and cognitive behavior between different pilots and helmsmen, and differences in behavior over time or for unique ships or channels for an individual pilot or helmsman. Research in this area must therefore be conducted to assure that a representative sample of subjects has been analyzed, in order to achieve a level of statistical significance transferable to the real world. The research methodology and examples presented in this paper appear to achieve these goals. Methodology The process for determining the requirements for safe navigation in restricted waterways was developed to address the following critical design and operational questions facing ship operators, port authorities, and regulatory agencies. . . . Which environmental conditions preclude safe navigation in the waterways? Which operational procedures for specific ship types enhance their safe navigation in the waterway? What level of safe navigation is provided by the aid-to-navigation system in the waterway, or what is the effect of alternative aids to navigation? What maneuvering characteristics are required for proposed ships to navigate the waterway safely? Is the level of safe navigation acceptable for a proposed ship type in a given waterway, or what changes in the waterway dimensions are required to ensure acceptable safety levels? All these questions must be addressed using methods that recognize it is performance of a human pilot exercising his capabilities in navigation that must be analyzed. Safely navigating a ship which is large for the channel is relatively routine for an experienced pilot - the ship is maneuverable and directionally stable, and there is no wind, current, or other perturbing influences, suab as banks or traffic. Determination of safety, given an adverse environment with allowance for the variability in response by the pilot, is the objective. The basic methodology consists of the following steps: 1. Define the characteristics of the harbor and its environment. 2. Define the operational characteristics of the ship. 3. Explore the interaction of the ship and the harbor in the presence of environmental conditions that limit a human operator's control of the ship during simulated harbor transits. Analyze the results of that interaction through appropriate measures of safe navigation performance.

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~6 The elements of these four steps are discussed in subsequent sections of this report. Step 1. Define Characteristics of the Harbor and its Environment Many categories of information are required to describe a port sufficiently for a comprehensive study of safe navigation. The sources of the required data, however, are few, consisting of 1) navigation charts, light lists, and current direction and velocity data for the harbor published by the National Ocean Survey, and 2) weather information and statistics for the area published by the National Weather Service. Information collected from these sources should be compared with and enhanced by interviews with mariners and weather observers who have extensive local knowledge. The categories of data required for a port study include the following: Waterway configuration - Channel widths and depths - Turn types and angles - Bank and shoal locations - Type and location of hazards Environmental statistics - Wind direction and velocity - Current direction and velocity - Visibility range - Unique current conditions Aids-to-navigation system - Types of aids - Characteristics and patterns (day and night) - Location of aids Operational policies and conditions Traffic rules and congestion Tug availability and size Limits on operations Types of vessels accommodated . The foremost limiting condition to large ships has generally been channel width and depth. To assess the general limitations of U.S. ports and waterways, the authors have developed a data base, resident in a computer file, which contains data on the physical channel characteristics of 32 major ports of the United States. Each straight channel leg and each turn in these harbors has been examined, and data on depth, width, aids to navigation, turn angle, etc., recorded. To assist naval arabitects contemplating design of future vessels, summary tables that characterize ports of the United States have been assembled from this data. These tables and the list of ports used are provided in Appendix A of this paper.

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57 Step 2. Define Operational 'Characteristics of the Ship Each question of safe navigation in a waterway implies a potential ship or family of ships. Normally, the problem involves the extension of the operating limits of the channel to allow passage of a larger ship or a ship of specific characteristics. It may involve guiding ships through a channel that has been restricted by, say, channel-side construction, or extension of port operational environmental limits to increase possible port use. In each case, a required component in the study is a mathematical hydrodynamic model of ship motion with the proper set of response coefficients for the ship's propulsion and control forces. Mathematical models of ship's motion have progressed to a stage at which there are a number of ship types available as models. Additionally, hydraulic model tests can produce good estimates for models' coefficients, given the ship's physical characteristics. Today's mathematical models include factors such as bank influence, shallow-water effects, bow thruster and tug boat forces, passing ship effects, and wind and current effects. Step 3. Simulation of Waterway Transits Under Operator Control The objective of the simulation is to determine how consistently, given the environment (ship characteristics, channel design, aids to navigation and possibly external help from tugsl, a pilot operating with a helmsman can navigate the ship through the channel safely. An appropriate simulator facility which can address this problem is the full-scale ship simulator. The ship simulator normally consists of a full-scale ship's bridge with all normal equipment. Typically, there is a method for representing the visual outside world, the radar image of the world, and the progress of the ship through that world. The motion of the ship through the world is driven by the computer, using the hydrodynamic model, which is in turn driven by signals from the steering stand and throttle on the bridge. The technology of ship simulators has been most advanced in the Computer Aided Operations Research Facility (CAORF) which is located at the Kings Point Merchant Marine Academy and is sponsored by the National Maritime Research Center of the Maritime Administration. At CAORF, a 125-foot cylindrical screen extending for 120 degrees to each side of the bridge portrays a computer-generated visual scene containing ships, shorelines, navigational aids, bridges, and buildings, realistically shown and moving in real-time response to the ship's movement. The visual scene can realistically simulate any level of visibility (fog) under night or day conditions. The visual scene is projected on the screen by special television projectors. The radar image is generated by a computerized radar signal synthesizer and is programmed to coincide with the visual scene. Pilots and masters navigating the ship experience the equivalent sensations and use the same information from the visual scene, the radar, and from the instruments as when navigating in the real world. CAORF has proved to be a valid, valuable tool for studying navigation performance with Oman in the loop. n CAORF

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58 has been used to study many port design problems, including those of Valdez, Alaska;t Puget Sound; 2 Point Conception, California; 3 Galveston, Texas; 4 Pascagoula, Mississippi;s and the Santa Barbara Channel. 6 A multiyear research program teas been maintained to systematically address a study of safe navigation in restricted waterways. Step 4. Analysis of Simulation Results and Measures of Safety To obtain the benefits sought in the methodology, performance measures must be defined that relate simulation results to safety. The objective of navigation in restricted waterways is primarily to maintain the position of the ship in the proper location relative to the channel boundaries or the channel centerline (i.e., establishing a proper crosstrack position). In the absence of traffic, the normal crosstrack position in straight channel legs is near the centerline. When meeting other ships, this position will shift toward the starboard boundary of the channel. The performance to be measured Is the consistency with which pilots passing through the channel can determine and control their crosstrack position, recognizing tbe necessity for tighter consistency near the channel boundaries than near the centerline. As will be discussed, measures of safety are principally descriptive of crosstrack variation. Along-track position in restricted waterways Is of minor importance, except in two instances. The first instance is the determination of the position to begin a turn, after which negotiation of the turn again becomes primarily a crosstrack and turn-rate control problem. The second instance is bringing the ship to a stop at some location. Measures of navigation performance in restricted waterways are therefore directed to measuring consistency of crosstrack position for repeated transits of the channel by many pilots under the same conditions. Changes in safety of navigation are defined by determining differences in the measures for changed conditions. Three principal measures have been derived and effectively applied across various experimental conditions. 1. The mean track location across the channel of the: Ship's center of gravity (CG), Port and starboard extreme points of the ship's hull. Statistical limits descriptive of the variability about the mean track: Standard deviation of crosstrack locations at points along the track, Location of the 95 percent limit of the track envelope of the CG. 3. Combined index. Measures 1 and 2 may be easily understood by considering the plot of these data along a sample channel. Figure 1 shows these data

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59 ;: ~1 ~l z. g g~ - - ~ - o - ~ - o - o ~ - v 5 ~ o Z~' o o o . ~o - o8 o I4E~I LINE I~EAN LINE . OF - ~, CG Of FORT EXTRE~E "INT _ 1 PORT IBOUNDARY . ~ . 1 l-WO STANDARD ~, DEVlATlOlIS OF / CG TRACK DISTRI~I~ EACH SIDE OF MEAN CG . hIEAN LINE -OF ST. . EXTRE~E ~INT ~e l . . , ST8D BoUNDiR Y . ~ l ~ . -o' ~i ',. _l _e -8 C" ~' I ~ 1. o ~ ~ -~ ~ iN: ! ~ C MB I~DEX DlSTA - E CR~TRACK (FT) . . y AID TO NAVIGATICN ~ ~ ~ ST-. . Figure 1. Plotted measurement of per formance. STANDARD DEVIATI~ OF CROSS TRACK ~ITI~ Figure 2. Combined index. / :; / \ MEAN TRACK LINE Of CG OF SHIP STBD CHANNE L / IBOUNDARY \ _ AREA USED FOR VALUE OF THE COMBINED INDEX

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60 plotted at 600-foot increments along a channel. The dashed lines indicate the channel edges, and solid lines indicate the mean tracks of the ship's CG and the port and starboard extreme points. The square symbols s bow the CG standard deviation doubled on either side of the CG mean point. If the distributions of crosstrack variance are assumed to be normal, this envelope would contain 95 percent of all transits. Measure 3 is called the combined index because it combines the mean ship position in the channel and the variation of the transits about that mean position. This combination has desirable features for predicting navigational safety in restricted channels. Neither the mean ship position across channel nor transit path variability alone give a complete description of safety. When combined in one index, however, the index can discriminate between tolerance for higher path variability when the mean track is far from the channel edge and the requirement for low track variability when the mean track is near the channel edge or when passing another ship, and assign both conditions a favorable value. The index computation is shown graphically in Figure 2. A normal distribution based on the standard deviation of the center of gravity point is centered on the mean crosstrack position of the CG point. The index value is the integrated area under the distribution curve which lies beyond the channel edge. The values of the combined index are plotted on the right side of Figure 1. The two curves are for the values relative to the port boundary (P) and starboard boundary (S). Insufficient data are available to test if the assumption of normality is correct. In fact, it is suspected that a truncated distribution may be more characteristic of the crosstrack variance as the edge is approached. The assumption of normality, however, is conservative, and sensitive to changes in pilots' performance. Since it is not necessarily the proper distribution, the index should not be interpreted as a probability of grounding. The values for the combined index included in this paper have been calculated relative to the mean ship center-of-gravity location. The process can easily be applied to calculate values relative to the mean port and starboard extreme point locations at along-channel locations. The index values for the starboard extreme point would be relative to the starboard channel boundary only, and the values for the port extreme point index would be relative to the port channel boundary only. The resulting index would reflect mean channel position, track variance, and heading error. Application of the Methodology to Port Design Problems: An Overview of Findings The Maritime Administration has conducted a series of experiments with their CAORF facility to evaluate the performance of navigation in restricted waterways. These experiments have investigated those areas of performance in which the master's, the pilot's, or the docking master's variability is likely to cause the ship to exceed safe operating conditions. The experiments have provided an initial

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61 understanding of the complex and interdependent relationships of harbor design parameters. They have uncovered a number of mitigating measures that can be applied in specific problem areas to achieve satisfactory performance in heretofore marginal situations. Six harbor design issues have been addressed at CAORF. These are: channel dimensions, environmental limits, operating procedures, tug requirements, aid-to-navigation requirements, and ship maneuvering requirements. The influence of each of these issues on the variability of masters, pilots, or docking masters is described briefly in subsequent sections. Specific data are not quoted in these sections, due to the large number of experiments from which conclusions were derived and the difficulty of comparing findings from specific experiments. Examples of performance measurement in several of the areas are presented separately in a succeeding section Examples of Analysis...". Channel Dimensions The adequacy of channel dimensions has been addressed in several harbor design experiments. Most recently, studies have been concluded on the Galveston ship channel, the Restricted Waterway Experiment" IIIA (8), and IIIB (9), and the Pascagoula ship channel. Experiments in channel dimensions generally addressed channel width, turn configuration, or both. Typically, worst-case wind and current combinations were selected. Experimental conditions tested whether subject pilots could safely maneuver in the proposed channel under the selected conditions. As a result of the wind and current variability and the requirement for the pilot to maintain a high drift angle against the wind and current, a ship's tracks displayed a high level of variability in crosstrack position both within runs and between runs. Although this variability does not show a large dependence on channel width, the channel width must contain it and allow for an additional margin of safety. Depending on the turn design (effective maneuvering radius allowed), the crosstrack variance in some cases was significantly affected when exiting the turn: the smaller the required turning radius, the higher the crosstrack variance during and exiting the turn. Analysis of performance in turns has indicated pilot control actions are initiated in anticipation of the turn. For small-radius and narrow turns, the pilot's anticipated actions must be accurate in magnitude and precisely timed. For large-radius turns, there is more room for error in the anticipatory actions, and for making corrective actions during the turn. Proper turn design has been shown to reduce crosstrack variation in a narrow waterway. -

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62 Environmental Limits The selection of appropriate wind and current conditions, and even the limits of visibility, is an important issue in any harbor design study. Typically, a ship operator or port authority specifies limits below which he requires 100 percent operation. Limits are defined by the frequency and distribution of local weather conditions and the economic consequences of occasional delays in delivery or shipment. In studies where the port is to be open to many operators (e.g., Galveston), environmental conditions are selected to provide, for example, 90 to 95 percent harbor availability based on weather and current statistics. The effect of environmental conditions on the ship and pilot are twofold. First, the ship must "crab" along the channel with a specific drift angle to maintain a ship's course equivalent to the channel course. Second, due to the presence of high drift angles, the pilot's perception of his position, and therefore the accuracy of corrective orders is degraded. Drift angle increases the "swept width" of the ship's path, thus occupying a wider portion of the channel. The effect of the degradation of the pilot's control process is to increase the crosstrack variability. The net effect of environmental conditions is thus seen to be a reduction in safety, placing the extreme points of the ship closer to the channel edges and increasing the crosstrack variability of those points. Current and wind combinations may also degrade performance in turns. Typically, the most severe effect evolves from a following current when the ship's ground speed appears high while the water speed is low, impairing maneuverability. Excessive windage can contribute to difficulties in turning depending on the topsides and superstructure configuration. In cases where environmental conditions degraded turn performance, crosstrack variation exiting the turn was high, and the only solution appeared to be widening the channel following the turn. Operating Procedures Many design studies involve handling ships in new harbors or modified waterways. Until recently, there was little experience in the United State" with oversized vessels (e.g., 150,000 DWT tankers and above). Most harbor design studies of today, however, involve accommodating such vessels in U.S. ports. With increased environmental pressures, authorities must consider establishing operational limits, be they environmental (wind strength, current cycle, etc.) or procedural (specified routes, speed, traffic conditions, etc.~. Procedures also need to be established that could act as mitigating measures to ship system failures. Several port studies at CAORF have addressed these issues: the Valdez tanker study, Puget Sound speed limit study, and Point Conception LNG* study. - *Liquefied natural gas e

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63 The issue of many procedural studies is to determine the safest approach and departure routes to a harbor across the environmental conditions. In Valdez, the departure route proved to be the design issue. By reducing a turn angle along the route, cro"strack variance passing by a middle rock was reduced. For the Point Conception operations, the evaluation of the approach route concluded that crossing an oncoming traffic lane would present little hazard. The findings of several port-related studier have indicated that safety may be inversely dependent on ship's speed over a limited range. The first impression is that slow ship speeds will be inherently safer. Data indicate, however, that with reduced speed comes a reduction of maneuverability and an increase in crosstrack variability. Increased speed not only increase" maneuverability, but also significantly reduces the required drift angle for adverse wind and current conditions. Tug Assistance Harbors planned for accommodation of oversized vessels often assume the use of larger shiphandling tug. than are generally available in U.S. ports today. Several port design experiments at CAORF have addressed the use and size of tugs for oversized vessel operations. Notable are the Point Conception Study, the Galveston Channel Study and the Pascagoula Channel Study. The use of tugs as rudders, and for slowing vessels by means of long lines astern, i" frequently practiced in Europe and Japan for oversized vessels, but has not yet received much attention in the United States. The interdependence of tug power and ship type and size with environmental conditions is important, but is yet largely unknown. A high-fidelity simulation of tug forces has been recently added to CAORF and will be applied in a number of experiments in the near future. Aid" to Navigation Visual aid" to navigation appear to serve as a mitigating factor to some of the perturbing environmental and channel design variables. Providing extra aid. in a channel has resulted in lower crosetrack variance and improved performance in difficult turns. Experimental conditions with fewer aids resulted in higher variance and unacceptable performance in channels of equivalent design and environmental conditions. Deficiencies in some harbor waterways might thus be overcome with additional aids to navigation. Evaluation of precise radio aid navigating systems teas been undertaken to evaluate potential performance gains achievable through a highly accurate positioning system. Data gathered so far indicate excellent trackkeeping performance. Just as visual aids to navigation, advanced radio aid systems may be employed to overcome marginal operating conditions in ports in place of port modifications, such as widening channels.

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- 64 Ship Performance The ef'fects-o'f ship cof~tol~a~ility on'variabi'1ity of 'trackkeeping has suggested that newly construdted''ships'might tee 'custom-designed for a specific pert or t'ype.of'wate`way. ING operations are particularly suitable for't. 8-i8 'typetof investigation'6ue 'to the ships' commitments to certain'termina-1-^s. 'I'' "''I'""' '''''' '" ' ' " ; " '''' An experiment'conducted'at ChORF"'indfcated that back'' variability increased~w1'th a-red~o'tia'n'i'n'th6' tbr'~ingiresponse of a Charge tanker. Tm~'rovem'ents'~n ma*-euvera'bili~ty Off' fa'rge'vess~el's using'-a'dvanced'desig'n- concepts~mat,'p'rove-'6ighly; behe'fi'cial 'to safe nav1'gat~ion'in restr'zcted' waters. ~-Of interest-is' rudder side, number 'of rudaers','~umber;-of ' propellers an8-perhaps`;bul1 'form.'; If higher turning moments could be pr~d'u;cdd at~ld'w`-spee'd''.(e.g.~,'.tWin.'-9ct'ews),'pe'rhaps'safe;;opera~elons could^8e~~con~ducted'~'at' very low;speeds.'~"Thirs are;a of' performance is still at the basic research level, but the gains to'be'ac'hi'eved are' '' ~ prOmlSlng e _. _ , . . . . ..... .. _. . ~. . . Examples of Analysis of Relative . ~ Navigational Safety in..Nar;row Waterways Specific compar'~sons'''.$'f navigatzon^performance'evaluationifor alternative ship character~stics,'channel design, and aids'to ' . . . navigation have been drawn' from two recent experiments at CAORF. During these experiments, Restricted Waterways Experiment Phase IIIA and IIIB, trained pilots navigated an 80,000 DWT tanker along a 500-foot-wide channel containing three turns connected by straight channel segments. This channel configuration is shown in Figure 3. Five pilots made transits through"the channel for each variation In a specific condition, providing a statistical basis for 'evaluating the - .. . .. .. . . . . relative effectts).of tbe.goodition on safe navigation. Results for these experiments have been reported in references'8 and 9. For this paper, several experimental conditions have been selected to illustrate the value of analysis of navigation safety using the measures previously described. Ship Maneuverability The amount of control force required to enable ships to negotiate waterways is one factor to be considered in the design of a new ship. There teas been a feeling among mariners that given enough training and experience, man is sufficiently adaptable ' to overcome difficulties with slow-re'sponding ships. The purpose of this comparison was to determine, in relatively severe environmental' conditions, what actual effect.a reduction of maneuverability would' have on safe navigation of a ship in restricted waterways. Would the pilots compensate for the slow response or would overall safety be reduced? ' ' For this experiment,'th'e'ship'was modeled with two alternative'' rudders. One rudder was the"standard rudder us'ed for an 8'0,"0'00 DWT

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65 tanker. The alternative rudder had only one-balf the effective area of a standard rudder. The results should be of interest to naval architects as well as port authorities and ship operators. The channel transits through the first leg, first turn, and second leg of the channel shown in Figure 3 were compared. The first leg required compensation for a crosscurrent, while the second leg had a following current. Graphic presentation of the results is shown in Figures 4, 5, and 6. The results show that the pilot was not able to compensate fully for the reduced maneuverability. Transits with the less-maneuverable ship resulted in greater variability in track position in the straight legs and turns, as illustrated by the crosstrack standard deviations. The mean track line is more sinuous on both straight legs for the less-maneuverable ship. The mean extreme point violates the channel boundaries in the first leg, as illustrated in Figures 4 and 6. The combined index values averaged along each segment are given in Table 1. In all instances, the more highly maneuverable ship allowed smaller combined index numbers. There is clear indication that with less-maneuverable ships, pilots require more channel width for safe navigation. Turn Configuration Turns in channels of the United States are generally of two types, non-cutoff turns and cutoff turns. The basic difference in the two types is that the vertex of the channel boundaries on the inside of the turn has been cut back on the cutoff turn, while it teas been left intact on the non-cutoff turn, Figure 7. The two types of turns are about equally common. Navigation through 30-degree cutoff and non-cutoff turns were investigated during the CAORF experiments. Graphic display of the results for turns is shown in Figure 8. Experienced pilots navigated cutoff turns more smoothly and safely than the non-cutoff type. Their mean cross-channel position through cutoff turns was close to ideal, while the combined index values are uniformly negligible. On non-cutoff turns, the pilots entered the turns and exited the turns wider and with greater variance in track line position. There is a focal point on non-cutoff turns at the turn apex at which the track variance is very low. The pilots apparently must pass through this point on the turn regardless of their position entering the turn and without regard for the effect on turn recovery. This effect is not apparent on cutoff turns where the pilots can establish a smooth curve through the turn and continue the line through recovery entering the next channel with a low crosstrack standard deviation. A rather dramatic reduction in the average combined index for the cutoff turn may be noted in Table 2.

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66 ` ~WIND ; ~ RENT 2 NM y~\NM VESSEL INBOUND FROM SEA l Figure 3 . Characteri sties of experi- mental channel. \ \\\' \ \ ', \ * ~ . ~ ' 1 hi. 1 6;. 1 ; 1 . ~ | d . -/ IQ turn. ~llj 350 ~ ~ no at. 1 O - race cam IT' o, Effect of rudder size in 0 I. TABLE 1. AVERAGE C - BINED INDEX CC~PARI SON FOR NO - AL AD SMALL RUDDY SHIP Average Combined Index Leg One Cross Current Turn Port ST8D Port STBD Normal Rudder . 151 .014 .085 .009 Emu 1 1 lludder .23 3 .260 .1 14 .226 Leg Two Followin ~ Current Port STBD I .029 L .os' . .00 .0 on _ _~ _1 00 250 500 00 250 DISTANCE CROSSTRACK (FT) 1. ~ Normal Rudder Leg I Small Rudder Leg 1 . 500 Figure 4. Effect of rudder size in Leg ~ 1 1 . 4 _. - o - . l ! . 1 ~ 1 ~ AWL RUOOl. LlD 2 MILL RU~OER tEC 2 .` Figure 6. Effect of rudder size in Leg 2.

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67 W :\ \ 500 -~ ~ ~"~"~: VN \ \ '\ \ \ V\$ ~\ N~\~\  ~\ \ \ \\ ~ :\ \ \ \ \ \ \ CU1.OFF 7UIt~ HO CUTOFF YU~ Figure 7 . Cutoff and non-cutoff turns . \^ CUTOFF TUIIBI \ ~ V, .-\\ V- ~\~- \ "ka _~. 30 KTS Figure 8 ~Ef f ects of type s of turns . ~ ~0w, 5. Figure 9. Experunental channels with and without midleg buoys. TABLE 2. EFF=T OF ~N CONFIGURATION ON COMBINED INDEX Turn Condition Non~cutoff Turn with Corner Buoys (Small Radius) _ _. Cutoff Twn with Geted Buoys (Larger Redius) _ Average Combined Index _ Port Starboard _ 0.056 O.032 TABLE 3. EFFECT OF ADD ING MIDL" BUOY Without treffic ~, n.~3 n~0ol ~I ~ _-i i ~ _ l, `,j, 1 . ~| `-1 1 ! ~, ~, ~i ss1 1 111: ~ . AVZ GE CO INZD NDEX _ | WITHOUT GATE | WITH ADOlTIONAL iATE 31 | | | | O PORt STBD PORT ST8D 3.| ~1 1 ~ ~ 1 . _ O.O0O O. 276 0.000 O.Og4 - 1 1 1. 1 _ _ o-~ c~-clt Im fUI~ F01~? ~ - TURN ~ - H0 ~IOLl. "n - ~e "n ~o Figure 10. Effect of adding midleg buoys on straight legs.

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68 Additional Channel Markings Many channels consist of a series of relatively short (1.5 to 1.7 nm) straight legs separated by turns. The turns must be marked so their position is known. It has not been clear, however, that the addition of buoys along the straight legs away from the turns is cost-effective with regard to increased safety. During the CAORF experiments, the second leg of the channel provided an excellent comparison of the effect of turn markings only versus the addition of gated pair of buoys midway along the leg. The two configurations are shown in Figure 9. The results are presented graphically in Figure 10. The average combined index values are shown in Table 3. Conclusions from this comparison are that the additional buoys clearly caused the mean track line to shift toward the center of the channel away from the edges and reduced the variance between transits. The combination of improved mean track line position and lower track line variance reduced the combined index values to essentially zero. As shown in Figure 10, these results clearly illustrate the potential use of aids to navigation to reduce crosstrack variance in certain channels and to increase the relative safety margin by holding the mean track near the channel centerline. Conclusions Performance data gathered from experiments with the ship simulator at CAORF have shown that a number of port design parameters directly affect piloting variability and navigation safety in narrow channels. The safe operational configuration of any port can be seen to be an appropriate combination of channel dimensions, operating procedures, limiting environmental conditions, ship maneuvering characteristics, and aids to navigation. Such combinations must yield a variability in trackkeeping performance that will fall safely within the defined channel for multiple ship transits. In this context, the design of any particular port is seen to be unique, each of the factors listed above providing specific limitations on the design parameters. The evolving experimental data base in port design from CAORF is increasing our understanding of the complex relation of piloting variability to safety and port design parameters. Using the methodology and experimental analysis developed at CAORF, we are now able to find mitigating solutions to many cases of identified problems that are cost-effective and that may have minimal environmental effects. The effectiveness of the present methodology is demonstrated by its ability to sense changes in all critical port design parameters. The formulated performance measures are effective in addressing the following requirements: Summarizing along-track performance; Identifying specific problem locations and reflecting changes required to solve them;

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69 . Providing numerical indices for comparison of relative safety. The final requirements of these measures will be to provide absolute indication of safety relative to actual behavior at sea. Measures indicative of the actual probability of grounding per transit will be sought over the next several years through extended experimentation at CAORF and at-sea data collection. References McIlroy, W., MA Review of Valdez Experiment,. Paper presented at First CAORF Symposium, National Maritime Research Center, June 1977. 2. Riek, J., S. Tenenbaum, and W. McIlroy, Can Investigation into Safety of Passage of Large Tankers in the Puget Sound Area, Report to the U.S. Coast Guard, October 1978. 3. Reese, W. Phillip, "Maritime Risk Assessment Applied to California LNG Import Terminals, n Proceedings, Second CAORF Symposium, National Maritime Research Center, 1978. 4. Tenenbaum, S., investigation of Navigation into the Port of Galveston, n Proceedings, Third CAORF Symposium, National Maritime Research Center, 1979. 5. Cook, R., "Investigation of Limiting Channel Conditions for LNG Transit into the Port of Pascagoula, Mississippi, n National Maritime Research Center Report, October 1979. 6. Mara, T., P.R. Keyes, and J. Puglisi, Impact of an All-Weather Precision Navigation System for Channel Navigation Performance and Ship Control," Vol. 3, Proceedings, Fifth Ship Control Systems Symposium, Vol. 3., David W. Taylor Naval Ship Researob and Development Center, Annapolis, Maryland. November 1973. 7. Bertsabe, W.R., A.J. Pesab, J.L. Maskasky, J.G. Clark, and D.A. Atkins, Study of the Performance of Aids to Navigation Systems - Phase I, An Empirical Model Approach, Report to the U.S. Coast Guard No. CG-D-36-78, July 1978. 8. Atkins, D.A. and W.R. Berteche, 9. IIIA, Data Analysis and Findings, National Maritime Research Center Report No. CA0RF-24-7802-01, October 1978. Atkins, D.A., W.R. Bertsabe, and R.A. Cooper, Restricted Waterways Experiment ITTB, Results and Findings, National Maritime Research Center Report, May 1978. Appendix: The Physical Characteristics of Waterways in 32 Major Ports Information covering physical characteristics and present aids to navigation of 32 major U.S. ports has been collected and entered into a computer data file. The ports selected and their regions are listed in Table 4. Using the most recent U.S. Coast Guard navigational charts, data descriptive of the physical dimensions of channel segments in each port were documented for each of the following four categories:

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t 70 TABLE 4. COASTAL REGIONS AND PORTS EVALUATION IN THE DATA B=E East Coast Portland (ME) Boston Providence New London New Haven New York Albany Philadelphia Baltimore Chesapeake Bay Norfolk Wilmington (NC) Charleston (SC) Savannah Jacksonville Miami Great Lakes _ Duluth West Coast . Long Beach Los Angeles San Francisco Portland (ORE) Seattle Juneau Valdez Honolulu Coos Bay Gulf Coast Tampa Mobile New Orleans Port Arthur Houston/Galveston . . Straight channel: the space between turns or larger areas of water that is delineated by dashed lines on navigation charts. Turn: a change in direction coming out of one straight channel and going into another. Bay: an open area of water with no dredged area or delineation of channels. Boundaries are land masses. River: as given on a chart. Boundaries are the river banks. The physical data compiled were channel width, depth, length, turn angle, and turn type (dredged configuration). The remaining data were code numbers and chart numbers that allowed retrieval of data from the computer data base and cross-reference to charts. When necessary, averaged widths of the rivers and bays were entered, and generally where there were different depths, the shallowest was chosen. Dashed lines delineating the channels on the charts were used as a basis for measurement. Depth is taken from the chart tabulation table or measured directly. Only channels with depths of 29 feet or deeper were considered for this analysis. There were entries for 835 channel segments, of which 47 percent were straight channels, and 46 percent were turns. The remaining 7

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71 percent were rivers and bends. Only the two larger groups by occurrence (straight channels and turns) have been tabulated. Straight Channels Straight channel depth and width for each port is given in Table 5. Figure 11 in a histogram that summarizes the number of channels by categories of width for all ports. It is apparent from the figure that the greatest number of straight channel segments are less than 600 feet in width and that the majority are either between 350 and 400 feet or between 550 and 600 feet. The distribution of straight channel depths is shown in Table 5. Turns Distribution of depths and widths of turns parallel the findings for straight channels. Physical data common only to turns are the types of turn configurations and the angles of turns. The determining factor of turn type (cutoff, non-cutoff, or bend) we" delineation on the navigational charts. A series of cutoff turns with extremely short (less than 1/4 nm) straight channels connecting them was counted as one bend, regardless of delineation. Bends amounted to approximately 50 nm, mostly in the ports of Houston/Corpus Christi. Figure 13 shows that of all turns sampled, more than 75 percent are 40 degrees or under, 34 percent are between 20 to 40 degrees, and another 43 percent are turns of 20 degrees or less. Of the 23 percent that are greater than 41 degrees, many represent turns on to a secondary channel. DISCUSSION JOHNSON: Does this apply to large bays and relatively shallow or dredged channels only, or does it also apply to approach channels, deep water, jettied entrances? BERTSCHE: It can apply to either problem. There are data bases that give the entire bottom, and the effect of shallow water comes in automatically. KNIER~M: The radius of the turn at several place" in New York Harbor where there are several marks for different circles in the same turn, necessitate" a different wheel. You have to increase the wheel to "et the "hip turning, then when you get in the middle of the turn, the arc flattens out and the radius becomes longer, and you have to ease your wheel, at times reverse wheel. At the end of the turn, you must increase the wheel sharply and get the ship "winging to stay on the course. Whenever possible, any turn, regardless of the degree

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72 TABLE 5. SUMMARY OF STRAIGHT CRANNEL DEPTE AND WIDTE FOR EACH MAJOR U.S. PORT (DEPTE IN FEET) - RARBORS WIDTH 400-500 500-600 600-800 . 35 40 35 35 35 35 35 35 40 40 32 32 31 35,33 35 35 35 35 42,40,45 45 40 40,38 40 38,39 34 42,38 38,35 36 36 40 42,40 40 36,33 40,30,38 45 47,47 42,40 45,30,35 35,30 40 40 40 40 l 350-400 800-1000 35 35 Portland Boston Providence New London New Haven New York Phildelphia Albany Chesapeake Baltimore Charleston Norfolk Wilmington Savannah Jacksonville Miami Tampa Mobile New Orleans Port Arthur Corpus Christ Houston Los Angeles Long Beach San Francisco Portland Coos Bay Seattle Juneau Honolulu Duluth 38 38 30 34,32 40 40 40,35 30 30 35 40 41,40 35 40 55 30 .

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73 of the turn, should have the same mark in the water and the same radius BERTSCEE: Yes, I would like to comment on that. In all my years of schooling, I really learned one thing in this area, and it became apparent as we looked at all the charts of all the ports to build a large statistical data base: all straightaways in the United States are connected by turn". m e turn is such a perturbative factor that attention to turning phenomena and their accommodation, if it can be facilitated, enables consideration of more narrow dimensions. .

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