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SHIP CONTROLLABILITY J.P. Hooft Introduction This discussion gives special attention to methods for taking ship controllability into account in designing a waterway. In evaluating the merits of a waterway tharbor entrance or port), economic considerations will be based on the comparison between the costs (building and maintaining) and the benefits (amount of cargo to be transferred in the port). Both the costs and the benefits are influenced by (among many other factors) the navigability of the waterway." When determining the navigability of the waterway, the controllability of the ships is an integral part of a complicated system. 2/3 For this reason, attention is increasingly devoted nowadays to the controllability of ships as traffic densities increase, maneuvering properties change (owing to the increase in the sizes of ships), and more ships carry hazardous materials. The controllability of ships Is determined by the combination of the ship's maneuverability and the actions of an appropriate ~ ~ In addition, one will find that for a given combination of ship and control systems, the controllability of the two-component system will change with environmental conditions (such as harbor configuration). For this reason, one should be more interested in the navigability of a waterway as determined by the effects of the total "ship-control-environment system" rather than in the maneuverability of the ships alone. Reluctance to determine the navigability of a waterway, or even to determine the controllability of ships in a given waterway results from the fact that such determinations do not hold generally. For each type of maneuver {approach, stopping, docking) in each type of waterway (approach channel, canal, port or berthing area at sea), different man-mach~ne control system.s/ 6/ 7 solutions will be found. Although the quantification of ship controllability will differ for each case to be considered, the method will always be based on operational research involving statistical descriptions of systems. The results of such studies provide the possibility of performing risk analysis. 75 \
76 Even in the face of the difficulties mentioned, it would be very beneficial to develop systematic information on the controllability of ships for various waterway configurations. This information would be most useful in establishing the preliminary design of the waterway. This preliminary design can then be evaluated and the design corrected and refined. This second attempt--consisting of one or two alternatives--will need a detailed study of navigational aspects, B taking into account the ship's controllability. These detailed studies are often performed by means of simulation techniques (in a model basins or simulators. General Description Throughout this paper, the term "ship" should be understood to denote Ship-control system. n Separate consideration of the inherent characteristics of the ship in the dual system will be indicated by the term ~maneuverability. n Since no uniform definition of ship controllability is presented in the literature, use is made here of the following description, illustrated in Figure 1: A ship is defined to be controllable when it can be handled in such a way that the deviation of the actual maneuver (described by all stated variables of the system) from the desired maneuver remains within pre-set limits. The essence of the description lies in two items: a. Knowledge of the discrepancy between the actual maneuver and the intended maneuver. b. Knowledge of the preset limits indicating the acceptability of this discrepancy relative to Abe available space (domain available for the maneuver). With respect to (a), it should be remembered that the ship's controllability will depend on the environmental conditions as they influence the actual maneuver. With respect to item (b), the environmental conditions influence the ship's controllability as they affect the degree of acceptability of certain risks. This interaction between the influence of the ship's controllability on the requirements of the layout of a waterway, and the influence of the waterway configuration on the ship's controllability, necessitates complex definition and analysis of the navigability of a waterway. The executed maneuver shown in Figure 2 brings out these points. Of the many possibilities, two will be discussed here. 1. Assume the preset limit reads: The controllability of the ship should be such that the ship will never hit the banks of the approach channel. The ship in this case is taken to be a tanker, and the banks are rocks. It now will be obvious that the maneuver actually performed deviates so much from the intended maneuver that the preset limit has been exceeded. The loss of control in this situation could have been caused by:
77 disturbance i=desired manoeuvre · i_ . 1 l ~ W:}' . S= ship characteristics O=actual manoeuvre S = inherent ship characteristics - ship's manoeuvrab~lity - = behaviour of controlled 1 ship ~ ship's controllability Figure 1. General description of the controlled ship by means of a block diagram. lo ! l ! l l l 1 ~ i l l l sh ip touches bank 1 1 l l Figure 2: Manoeuvre performed with a simulated ship entering a harbour through a dredged channel.
78 a) Inadequate ship maneuverability, b) c) Inability of the mariner to control the ship, Malfunction of hardware elements in the steering system or the navigational aids, d) Poor channel conf figuration, or e) Unacceptable environmental conditions such as wind, waves, or currents. 2. Assume the preset limit reads: The controllability of the ship should be such that the banks will only be hit by a ship once in, for example, 10,000 passages through the channel. In this case, the channel bottom is muddy and the ships are dry cargo ships. It now will be obvious that the controllability of the ships passing the waterway is acceptable when the executed maneuver is a rare example of many maneuvers during which the banks have been cleared. Since the ship's controllability depends on so many items, it might be of interest to ascertain a basic value of controllability for a given ship. This value is principally sought to serve as a reference. Such a reference value would represent controllability resulting in minimum deviation between actual and projected maneuvers, or in other words, the ship is optimally controllable when it performs maneuvers that show the closest agreement with the hypothetical maneuver designed for the waterway. In the paper by the SNAME H-10 panel, the suggestion is offered that this reference value be def ined as the n inherent controllability. In addition to this suggestion, the following considerations might also be of interest. Returning to the description of ship's controllability, for the allowance of deviation of the actual maneuver f rom the intended, some area is required at each stage of the passage if many ships pass. This so-called width of lane can only be determined with some chance that the ships will pass within the area. According to the S NAME H-10 panel, this width of lane is determined by the piloted controllability of the ship. The reference (optimal) amount of piloted controllability is called "initial controllability, n and can be defined as that amount of controllability for which the width of lane will be minimal for the situation considered, ignoring all types of disturbances. To s bow the difference between this latter concept and the definition of the H-10 panel, the following observations can be made: . Inherent controllability refers to the best abilities of the ship resulting from its maneuverability characteristics. Initial controllability refers to the best behavior of the ship resulting from the combined effect of "ship-controller-waterway" characteristics. For the evaluation of the navigability of a waterway, both considerations--~inherent controllability" and "initial controllability" (= best piloted controllability)--have to be considered to arrive at a most beneficial waterway design (minimal costs and risk of accidents).
79 A hypothetical example will be discussed in the next section to elucidate the analysis of ship's controllability in a particular waterway. Considerations in Designing a Port Starting Points of the Design A harbor is to be designed alongside a coast for the docking of LNG carriers only of 125,000 ma or smaller. (The schematic plan for the design is illustrated in Figure 3.) The port is to accommodate the arrival of 136 ships per year over a period of 20 years (about 5500 passages in the harbor). In the approach channel, the ships sail through currents and waves, while the channel depth is designed for 15 percent keel clearance to the ship. The maximum current amounts to 3 knots while the ships sail in prevailing winds of either 5 Bft or 8 Oft. The first decision to be made is the approach speed of the ships. Assuming a 2750 m length for inner and outer harbor--based on experience from earlier studies--it is stipulated that the ships will pass the outer piers at a speed of approximately 5 knots, with a maximum variation of 1 knot, while 4500 m in front of the outer piers their velocity is 8 knots. The port design will also be based on the fact that the tugs will fasten inside the outer harbor region. Another shore-based decision for the design stipulates that only one ship at a time will approach and dock in the harbor. At this stage, the question arises what the dimensions of the approach channel (to be dredged) and the distances between the piers should be. When design charts for the width of shipping lanes are available, a compromise can be attained for the optimum harbor mouth. This compromise would fall somewhere between as wide a harbor mouth as possible for navigational purposes and as small a harbor mouth as possible to minimize wave penetration into the harbor. Exploring the waterway dimensions required to facilitate the entry of ships into the harbor, the inherent controllability will lead to a width of the approach channel dependent on the ship's drift angle against current and wind, while the dimensions of the harbor mouth and the area behind it will depend on the current shear in front of the outer piers. Further exploration will show that the initial controllability of the (piloted) ship leads to the following design alternatives, assuming the ship approaches a channel 500 meters wide under conditions of no current, but some wind disturbance typical of normal operations. Design Alternative A Available width of outer harbor mouth 500 m Required width of lane in the approach channel -290 m Required width of lane between the outer piers -240 m
80 outer piers inner piers at Cal ,rre . I ~ approach channe 1 ( dredged ) outer .~ inner harbour ~ harbour L berthing area leading 1 ine of 1 ight s 900 m 1 850 m Figure 3. Schematic plan of the design.
81 . Required width of lane in the outer harbor ~30 m Design Alternative B Available width of other harbor mouth Required width of lane in the approach channel Required width of lane between the outer piers Required width of lane in the outer harbor 300 m -600 m -220 m -245 m The results presented in Figures 4 and 5 have been reduced from the average value and standard deviation of many maneuvers of ships entering the harbor in the conditions specified. For the winds blowing from starboard, half the required width of lane is determined by the average and the standard deviation presented in Figure 6. Assessment of Initial Controllability Before comparing the two options to be developed, more attention is devoted to the theoretical meaning of the information provided. The question arises: are the required widths of lane in Figures 4 and 5 completely described by the initial controllability of 125,000 m 3 LNG carriers in the harbor considered? This question can be answered affirmatively if all boundary conditions {ship speed, prevailing wind, etc.) mentioned in the starting points of the design are taken into account. This means that in the option of an outer entrance 300 meters wide, the ships' controllability is such that an approach channel at least 600 meters wide is required. The channel width has to be 600 meters sat least, n because the initial controllability is considered to provide the minimum deviation between actual and intended maneuver. During normal operations, the ship's controllability will be less (leading to larger channel widths) than the initial controllability, as will be shown later. The navigability of the waterway can only be improved when the starting points of the waterway design are changed or by reference to another ship system (maneuvering characteristics of the ship in the combination-of-control method). The controllability of the ship can be improved, for instance, by giving the pilots special training, by providing other aids to navigation to the pilots, 12/~3 or by increasing the water depth, by which the turning ability of the ship increases. Taking these additional considerations into account, it can be assumed that from a practical point of view, the results presented in Figures 4 and 5 represent the initial controllability of the 125,000 m3 LNG carrier in the two alternatives.
82 - L 500 m 290 m 240 m 230 m required width of lane Figure 4. Initial controllability of ship in design alternative A. ~ l _~_ ~ ~ 600 m 300 . l m 220 m required width of lane 245 m SOO Figure 5. Initial controllability of ship in design alternative B. approach channe 1 . ~ 4) 4, E ~ a. 2 5 m _ ~ · - - 5 0 m _ o SO m_ Oc 25 m~ ·. - ._, Q. c v up o outer piers outer harbour 4 km3 km 2 km 11 1 1 km ~ centre of channe 1 __~ 4 km 3 km 2 on 1 km width of outer harbour mouth 300 m 500 m Figure 6. Description of the ship 's tracks in design alternative A or B.
83 Assessment of Ship's Controllability in the Design Port In order to proceed to the design of the harbor, some decisions have to be made from a practical point of view. For example: At this stage, changing the starting points of the design to improve the initial controllability of the ship is not recommended. It is assumed that a harbor entrance of 500 m is acceptable from the point of view of wave penetration in the berthing area. Widening of the approach channel from the point of view of initial controllability of the ship has to be rejected. Based on these arguments, the development of the harbor design now continues with alternative A presented in Figure 4. It is decided that the time ships wait to enter the port at an appropriate current velocity has to be minimal. When the ships have to enter the port at any moment of the tide, the following values are found: Required width of lane in the approach channel Required width of lane in the outer entrance Required width of lane in the outer harbor Required width of lane in the inner entrance -620 m -410 m -525 m -385 m With respect to the values indicated in Figure 7, the following comments should be made: 2. 3. 1. The widths of lanes determined are preliminary values that hold only for the initial design stage, in which the starting points of the design have not yet been evaluated from economic, hydraulic, and other points of view. The widths of lanes have been determined in a more or less ideal environment in which, for instance, the visibility is clear and information about the current speeds is known to the pilots. When the hydrographical information to the pilots is not accurate, then the waterway has to be much wider to allow the pilot to experience the environmental conditions in which he is sailing. The widths of lanes have been determined using the average track and standard deviation of many maneuvers, as shown in Figure 8. For the determination of the width of lane, it is assumed that there is a chance (P) of 50 percent that never during the 5500 maneuvers in the waterway will the width of lane be exceeded. When taking into consideration the number of extreme deviations of an outer point of the ship (taking into account ship's length and breadth) from the centerline of the waterway, one finds n = 6930 extremes during the 20-year lifetime of the harbor considered, leading to a chance (1-p) of
r 84 Boo ~ m 5~ ~ L 385 required w, dth of lane Figure 7. ;25 m_ I ~ . - SO m_ m Required width of lane of the ship in the first draft design. approach channel 4 km :3 km - outer piers inner piers 1 , , , , ~ 1 /1\ 1 2 km 1 km - / i~ ·_i ._, 0 In n .. 0 o 4 km 3 km 2 km 1 km Figure 8. Description of ship's track in the first draft design (see Figure 7) -
85 O.9999 percent that the largest extreme will not exceed the boundaries of the width of lane (P = (l-p~n). Based on the chance p of 0.0001 percent of exceeding the boundaries, these are determined by a factor n, the relation of the maximum and the standard deviation: n =~-2 In 0.0001 = 4.29 (average) from which w = 2 (n om + am) in which w = required width of lane om = standard deviation of plots of extreme points of ship am = average value of plots of extreme points of ship. 4. The values shown in Figure 7 are a consequence of the high level of safety used in the calculations presented above. However, in the initial stage of design, the harbor dimensions seem acceptable relative to the controllability of the ship considered when one neglects these required widths of lane, instead considering the chances of exceeding the given waterway dimensions. One then obtains the following picture: chance of exceeding dimensions of an extreme in the 500 m approach channel p = 0.015. chance of exceeding dimensions of an extreme between the 500 m outer piers p = 0.001. chance of exceeding dimensions of an extreme in the 500 m harbor p = 0.004. From the preliminary values in Figure 7 (determined by the ship's controllability), it can be decided that a first-draft design of the harbor can be: width of channel 500 m width of outer entrance 500 m width of inner entrance 500 m This draft plan should be further evaluated from hydraulic and economic aspects. It is advised that a detailed draft developed in this way be tested afterwards for its navigational merits. In such a final nautical study, a search can be made for optimum navigability by improving the ship's controllability through a variety of measures specific to the harbor. In such a detailed nautical study, due attention should also be given to real-life disturbances that exercise an adverse influence on the ship's controllability. Suab disturbances include the breakdown of machinery onboard the ship, failures in connecting tug boats, and hindrance of unforeseen obstacles (e.g., maintenance dredges).
86 Finally, the values presented in this section have been determined from experiments performed at the Netherlands Ship Model Basin ship maneuvering simulator. These figures hold only for the conditions of this specific harbor design and cannot be copied for any other situation without correlation to a range of experiences acquired under other conditions. The figures have been used in this paper only to demonstrate the recommended line of thinking for assessing the ship's controllability in the design of port and harbor entrances. Effect of Ship's Controllability on the Navigability of a Waterway It has been noted in the preceding section that many factors will influence the controllability of a ship in a waterway. Decision makers must consider such factors as acceptability of ship size, ship speed, tug assistance, aids to navigation, and others In relation to the available water depth, width of waterway, current patterns, and layout of the port (recommended maneuver). It will be of no interest to assess the influence of these factors within some subsystem (as for instance, the influence of tug boats on the turning ability of the ship, or the influence of position information on the performance of the pilot). On the contrary, each factor can have tremendous effects on the total system (the piloted ship in the waterway). The controllability of a ship has been described to this point by the performance of the ship indicated by the deviation of the actual maneuver from some reference maneuver (an intended maneuver or desired maneuver). To assess the navigability of the waterway in a broader sense, one should consider the sensitivity of this performance. In this respect, a very important aspect of the navigability of a waterway is the description, "ease of performing a given maneuver (sailing through the waterway) during operational conditions." The following example illustrates this idea. Compare approach channels, both 300 meters wide, to two different ports, A and B. For port A, the width of lane is required to be 290 meters for ships of different types while port B is designed for a specific type of ship for which a lane 200 meters wide is required. When the chance of an accident in port B is large for a ship that differs slightly from the specified type, then it will be obvious that the navigability of port A is more acceptable than that of port B. The same illustration could be given for the influence of the approach speed on the navigability of a port: the conditions in some ports are such that a variation in the approach speed will not affect the required width of the lane, while in other ports such a variation can lead to undesirable risks. From these examples it will be understood that the navigability (indicated by "the ease of sailing through the waterway") depends largely on the sensitivity of the ship's controllability to disturbances in daily operational conditions. The general definition of sensitivity leads to the following:
81 Ap/p AK/E in which s = sensitivity--the navigability Improves when s becomes smaller P = performance of the ship determined by its controllability AP = change of performance E = external factor influencing the ship's controllability AE = change of external factor When the external factor changes randomly, then the quantity ~ can be indicated by the standard deviation of the varying factor, while E is the average value of The varying factor. In this case, UP is indicated by the standard deviation of the performance index of the ship's controllability. As no routine exists for developing harbors from a nautical point of view, no methods have yet been developed to analyze the navigability of a waterway according to the paraphrase given above for the sensitivity of the ship's controllability to external disturbances. The most important missing aspect to develop for the analysis of the navigability of a waterway is criteria. In the future, when experience has been gained in using the term "navigability of a waterway, n practical criteria can be developed that provide a common-sense understanding of the acceptability of the waterway from a nautical point of view. In the absence of criteria to answer the question whether a waterway is acceptable when the sensitivity s is known, an elaboration of the meaning of the paraphrase for the sensitivity s will be given here with the help of a few examples. Example 1. It was seen in the previous section that in zero-current conditions the required width of lane in the approach channel changed from 290 m to 600 m when the width of the port entrance changed from 500 m to 300 m. The sensitivity of the ship's controllability to the 500-meter entrance will be: 310/290 s = --- = -2 ~7 we -200/500 ~ in which S D sensitivity to the width of entrance. we The sensitivity swe of the ship's controllability at a 300-meter- wide harbor entrance is -0.775. The conclusion now reads: the controllability in the approach channel is acceptable with a 500-meter
88 . wide harbor entrance; however, the sensitivity to the width of the harbor entrance is large. Small changes in the width of the harbor opening will have large effects on controllability. However, in the 300-meter-wide harbor entrance, the ship's contrc~-ability is unacceptable, while its sensitivity to the width I-- the harbor entrance is small. Little gain in controllability can be achieved by widening the opening' Example 2. It was seen in the previous section that for the design concept A, the required width of lane in the approach channel changed from 290 meters when there was zero current to 620 meters when the ship had to sail in a variety of crosscurrents with a maximum speed of 3 knots. Since the external factor (current velocity during each maneuver) is randomly changing, the sensitivity to current is a little bit more complicated than in the previous example. From the maneuvers performed one determined: Required width of lane: 290 m at zero current Required width of lane: 480 m at currents with a magnitude of either -1.5, 0, or +1.5 kn during various maneuvers Required width of lane: 620 m at currents with a magnitude of either -3, -1.5, 0, +1.5, or +3 kn during various maneuvers. When it is assumed that the 290-meter width of lane is indicated by the initial controllability of the ship in the design port without disturbances (no current), then the 290-meter width of lane is the initial (zero) width to be considered for the port. An additional 190 meters of width is required when the port is designed for ships to enter during crosscurrents of 1.5 knots maximum (see Figure 9~. However, when the port is designed for ships to enter during crosscurrents of 3 knots maximum, then 290 meters has to be added to the required width of lane at the initial controllability. In this way, one finds a sensitivity to current of 1 at zero current (~P/~E = P/E at E ~ current velocity = 01. Note: this amount of sensitivity has no absolute meaning, as it is used only to define a relative measure to the sensitivity at higher values of the crosscurrent. The sensitivity to currents of the ship's controllability in the design port is presented in Figure 9. From the results obtained earlier, it was concluded that the ship's controllability decreases at increasing current velocity: P (required width of lane}, and increases at increasing E (current velocity). However, it can be seen from Figure 9 that the port designed for ships entering as various currents reach the maximum velocity is considered the best navigable port when the channel width corresponds to the required width of lane. Note: this conclusion would have been reached much easier by considering ~P/~E. This latter consideration, however, only applies to the present case, and has been ignored because it seemed more interesting to show the general meaning of the definition of sensitivity offered previously.
89 w a 300 m 200 m 100 m O m 100 m m/see Aw /A a c w = additional required width of lane when the port is designed for ships entering at current velocities which are maximal as indicated on the base `~ : _ . _ - - _ O kn 1 kn 2 kn 3 kn 4 kn , , , 1 current velocity Aw /Ac . _ Aw /w a a Ac/c 1 -__ 1 , , , 1 O kn 1 kn 2 kn current velocity Figure 9: Schematic indication of reduction of the sensitivity to current. 3 kn 4 kn
go Example 3. In reference 14, the controllability is considered of a 200,000 OWT tanker sailing through a crosscurrent of 0.5 knots average. A peak exists in the crosscurrent of which the amplitude varies between 1, -1.25, -1.5, -1.75 and 2 knots during various maneuvers. When the exact magnitude of this peak is known to the pilot, a required width of lane of 350 meters is observed. However, when the information to the pilot about the magnitude of the peak current is less exact, then the required width of lane increases to: 410 m at an accuracy of 87% 670 m at an accuracy of 75% One thus finds: sad= 60/350 = 1.32 for 100% accuracy 13/100 sad= 320/410= 2.72 for 87% accuracy 25/87 sad= 260/670= 2.42 for 75% accuracy 12/75 in which: Sal = sensitivity to accuracy of information. From the above results it can be concluded that the navigability of a 350-meter-wide waterway with 100 percent accuracy of information about the current is better than the navigability of a 670-meter-wide waterway in which the accuracy of information about the current is 75 percent, while this latter design offers better navigability than a 450-meter-wide waterway in which the accuracy of current information is 87 percent. In other words, from the results obtained, one could recommend a choice between two alternatives. Alternative 1 is a waterway of restricted dimensions in which correct information about the current is supplied to the mariner. Alternative 2 is a very wide waterway in which the information about the current to the mariner is only a rough estimate. Safety of Navigation In the preceding sections, the navigability of a waterway, as influenced by the ship's controllability, is regarded only from the point of view, more or less, of economical operations. Some attention teas been given to the optimum use of a port: as many ships should enter the port as easily as possible under most conditions. However, when considering the controllability of the ship during its passage through the port, the ultimate test is the mitigation of
91 accidents. Of course, the safety of navigation depends largely on the ship's controllability, but the execution of a risk analysis will cover more than ship controllability alone. Though the navigability of a waterway is closely related to the safety of navigation in the waterway (and both are influenced by the ship's controllability), different procedures will be employed to specify each. A true risk analysis necessarily implies a three-step procedure. The first step includes the establishment of the probability of the occurrence of hazards and their associated consequences. (This would presumably include human errors that initiate a chain of events creating a hazard). The second step is an evaluation process to determine the level of risk the system is expected to be subject to, and the third step is the procedure whereby the originally derived level of risk is mitigated by the introduction into the system of certain design changes, actions, operative restrictions, and other factors. In evaluating any marine transportation system from the point of view of safety, one must utilize a systematic process that infers the level of safety from the aggregate of the individual risks, rather than the individual risks alone. This in itself suggests that a systematic process of risk identification and analysis is necessary to measure the safety of a system. The problem to date has been the inability to derive a systematic evaluation process that correctly considers all the complex interactive elements that contribute to the occurrence and activation of hazards; namely, The ship's inherent hydrodynamic characteristics, The ~skill" of the mariner in controlling the ship, The peripheral aids (either on board or external to the ship) that furnish data or control to the mariner, and The effects of a particular environment (port geophysics, wind, current, channel width and depth, other vessels, etc.) on the vessel and the operator. To approach this complicated problem, it is of primary importance to acquire reliable data from actual practice. To this end, good correlation must be available between what in fact occurred and the reports of persons involved. It is no surprise that accurate measurements are limited by instrumentation and the conditions under which marine casualties occur. Moreover, human perception is highly subjective. This has led to the generally accepted theory that there are more accidents than are actually reported. This problem can only be solved when the reports are scrutinized more closely and the hypothesis that accidents are intentionally concealed is disregarded. Another discrepancy in the reporting system derives from the physiological and psychological characteristics of men involved at the time of an accident. Since among other things, a clear definition of mental load is lacking, it is difficult to establish a criterion of Allowable stress.
92 Concluding Remarks Ship controllability exerts a large influence on the navigability and safety of a waterway. In assessing a ship's controllability, no absolute measures can be defined because many factors related to the properties of the ship and of the waterway are important. To reach an improved understanding of a ship's controllability as it determines the nautical requirements to be imposed on the dimensions of a waterway, more basic research must be conducted. The results of such investigations would provide port designers the information to set up a first-draft design of the port. When such a draft has been evaluated from economic, hydraulic, and other points of view, adequate means are available to ascertain the final merits of the port from a navigational point of view. References 7. 1. Van Dixhoorn, J. et al., "Development and Criteria for the Design and Construction of the Port Approach and Harbour Area Entrance of Rotterdam Europoort, n Paper presented at Symposium on Aspects of Navigability of Constraint Waterways, I.A.H.R., Delft, 1978. 2. Keith, V. F. et al., Realtime Simulation of Tanker Operations for the Trans Alaska Pipeline System, n Paper presented at Annual Meeting of The Society of Naval Architects and Marine Engineers, New York, 1977. 3. Hooft, J. P., "Handling of Large Ships, n Paper presented at West European Conference on Marine Technology, The Hague, 1974. 4. Mandel, Ph., "Ship Maneuvering and Control, Principles of Naval Architecture (New York: Society of Naval Architects and Marine Engineers, 1967~. Crane, C. L., Jr., Estate of the Art on How to Include Human Control into the Method of Investigation, n Paper presented at Symposium on Aspects of Navigability of Constraint Waterways, I.A.H.R., Delft, 1978. Paymans, P. J. "Human Factors in Shiphandling, n Paper presented West European Conference on Marine Technology, London, 1977. Hooft, J. P., et al., "The Influence of Human Behaviour on the Controllability of Ships, Paper presented at Spring Meeting, Society of Naval Architects and Marine Engineers, New London, Connecticut, 1978. 8. Hooft, J. P., The Influence of Nautical Requirements on the Dimensions and Lay-out of Entrance Channels and Harbours, n International Course on Modern Dredging, Technical University, Delft, 1977. 9. Boylston, J. W., "Is Port Study Model Testing Really Worthwhile?" Marine Technology, 1974. 10. Hooft, J. P. and P. J. Paymans, Four Years' Operations Experience with the Ship Control Simulator," Paper presented at S.T.A.R. Symposium of The Society of Naval Arobitects and Marine Engineers, Washington, D.C., 1975. at
93 13. 11. Panel H-10 of The Society of Naval Architects and Marine Engineers, "Proposed Procedures for Determining Ship Controllability Requirements and Capabilities, n Paper presented at S.T.A.R. Symposium of the Society of Naval Architects and Marine Engineers, Washington, D. C., 1975. 12. Van Dixhoorn, J., "Feasibility and Profit of Navigation Information and Navigational Aids Offshore, n Paper presented at 23rd International Navigation Congress of the Permanent International Association of Navigation Congresses, Ottawa, 1973. Atkins, D. A. and W. R. Bertsche, "Evaluation of the Safety of Ship Navigation in Harbours, n Paper presented at Spring Meeting of the Society of Naval Architects and Marine Engineers, Coronado, California, 1980. . Oldenkamp, I., and P. J. Paymans, influence of Cross Current in a Channel on a Man-Steered Ship, n Paper presented at National Meeting on Simulation for Service of Traffic, Bremen, 1975. Porricelli, J. D. and V. F. Keith, "Systematic Processes for the Marine Decisionmaker in Regards to the Safety of the Waterborne Carriage of L.N.G. in Bulk, n Testimony before Senate Committee on Commerce, Washington, D.C., 1974. DISCUSSION WEBSTER: In your Figure 7, you show a required mean width of lane. As a result of the studies you conduct, is that the width you recommend to be dredged? If you were trying to minimize port costs, would you dredge the lane that way, or would you try something else? HOOFT: For these figures, suppose you had 500 meters available, and available information indicated that you required 620 meters. Then I would say, look at the higher requirements you would apply to this figure; for example, "I want 50 percent safety over 2000 maneuvers of ships," etc., and when you look at the other possibilities available for mitigating the chance of accidents at 620 meters, then I would say which is the just concept or first draft? Then look to see if 500 meters is acceptable from a hydraulic point of view. Do you have acceptable wave penetration in this inner harbor? Is the wave penetration of the docked ships excessive? Then you must take other measurements. For designing a harbor, you want some indicative requirements for deciding dimensions: information about controllability, for example. Then you must look from all the other points of view to see if the evolving design is acceptable for the controllability assumed and for safety. KRAY: The maneuverability of the ships you discussed, is that for an automatically controlled ship excluding all human elements. For example, is the delay in the transmission of orders to the engine room considered, or the response of the ships to the actions of the handler? It appears that you have considered rudders of the conventional type in these studies. Have you given attention to the
94 flat-belt type that is far more effective in keeping the ship on course and in preserving its maneuverability? HOOFT: What you are indicating is that the total system is composed of so many aspects' The human element you mention, for example. Your question is, was the skill of the shiphandler considered in the performance of the maneuver? The overall system can be improved by increasing the skills of the people involved. The ship's maneuverability can be influenced by the rudder configuration, the stern configuration, the dimensions of the ships. My plea in making this presentation is that when you are not satisfied with the ship- harbor interaction, it will not do--as was common 10 years ago--to blame the dimensions or characteristics of the ships. In the past three or four years, it has become common to cite human error. In another four years, the blame for accidents may fall on the navigational aids' Elements of the system cannot be singled out, as you and Bill Webster indicate by your questions. The decision about channel width and any other in the design is a compromise effected among all the concerns the designer is trying to meet, most importantly, the navigability of the waterway. HARDOW: On one hand, we're talking about balancing the capital costs and the operating and maintenance costs of a whole series of steps one might take dealing with the ships, the harbor, the channels, and so forth. On the other hand, we're talking about accidents. We should be looking at the consequences of certain kinds of accidents that will occur if proper steps are not taken, and the costs. We have never tried to do this in a systematic way that I know of, but if we did, we would have to look at other items, and make a full systems analysis. SEARLE: I want to endorse that. There is too great a tendency when an accident happens--and all I see is accidents--to cite human error as the cause. I've seen many accidents that were inevitable. The unusual aspect of many accidents is that more bave not occurred in the same place. There have been two major accidents in Tampa Bay since the first of the year. Both were inevitable. Seconding what Gene Harlow said, systems analysis ought to pinpoint those hazardous locations. Your presentation highlights the integration of ship maneuverability or controllability with harbor design: the system also needs hazard" analysis, failure mode and effects analysis. CRANE: I'm fully in accord with full systems analysis. We must accept certain constraints and givers: while it would be helpful if all shiphandlers were fully trained, for example, their range of ability must be accepted. Then we are in a position to work with channel dimensions, aids to navigation, vessel traffic systems, and other parameters to improve safety.
