While the above data relate to stopping from full speed, we believe a more important matter involves stopping from a slow maneuvering speed such as 6 knots. Table 2 summarizes approximate reductions in stopping distance for various design changes for a VLCC operating at 6 knots. For most of these design changes, the reduction in stopping distances must be called significant. Yet a one-knot reduction in maneuvering speed can overshadow the effect of any of these design changes. To state it more precisely, a tanker operating at 6 knots can reduce required stopping distance by 20% with a reduction in speed of just .6 knots. Therefore, the advantage of using a somewhat slower maneuvering speed must still be stressed even at the slower speeds normally used in channels. Finally we should mention that research is proceeding on a number of possibly promising maneuvering devices not previously discussed. Included among these would be a steering Kort nozzle as shown in Figure 11, and a rotating cylinder rudder as shown in Figure 12. Each of these devices have shown both at model scale, and in smaller ship installations a proven capability for reducing turning circles and helping a vessel to stop under directional control-that is, on a predetermined course. The real questions center on whether there is any need for such devices on large tankers, and if so the mechanical means for applying them to VLCCs. Far more research is needed before either of these questions can be answered. SUMMARY This is not a paper from which hard and fast conclusions can be drawn. Nonetheless, it is our hope that it has given an over-view of some of the technical aspects of large tanker maneuvering, as well as an appreciation for work underway in this field and the capability for reliably predicting large tanker maneuvering performance. More needs to be done, however, particularly along the following lines: As pressures mount to specify maneuvering performance of tankers, a rational definition of what is meant by maneuvering must be evolved. This definition should include not only ship and control force capabilities, of the types described herein, but consideration of environmental and physical limitations in port areas together with rational methods of controlling traffic in such areas. Accordingly, it is a coordinated task for mariners, ship operators, and technical people with both ship and harbor design backgrounds. More work must be done to produce the most useful form of presentation for ship maneuvering data to mariners. In all of the above, greater use of ship handling simulators is encouraged not only for personnel training, but for research studies fitting tankers and other large vessels to harbor environments. In closing it is appropriate to describe one of the key technical findings of our maneuvering research programs in laymen's terms, since we think it adds an important perspective to studies of tanker maneuvering problems. Our research has clearly shown that a good man handling a poor ship is a far better combination than a poor man handling a very good ship. We believe this finding is particularly pertinent when one starts to consider measures needed to prevent ship accidents. |