Problems and Opportunities in the Design of Entrances to Ports and Harbors Proceedings of a Symposium (1981) / Chapter Skim
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Evaluation of the Safety of Ship Navigation in Harbors
Evaluation of the Safety of Ship Navigation in Harbors
Pages 53-74
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From page 53... ...
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.
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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.
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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.
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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 .
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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.
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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)
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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.
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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.
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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.
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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.
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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.
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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.
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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 .
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_ 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 .
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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.
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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.
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Seattle Juneau Valdez Honolulu Coos Bay Gulf Coast Tampa Mobile New Orleans Port Arthur Houston/Galveston .
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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.
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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".
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