Implications of Performing Tugboat Stability Analysis with Fixed Trim Assumptions
JMS published a technical paper Implications of Performing Tugboat Stability Analysis with Fixed Trim Assumptions that they presented at the Society of Naval Architects & Marine Engineers (SNAME) 2010 Annual Meeting in Bellevue, WA.
Tugboat and towboat stability analysis may be performed with either “fixed trim” or “free to trim” methodologies under the current Code of Federal Regulations (CFR). The “fixed trim” method allows the vessel’s draft to change with increasing heel angle, while maintaining constant trim until the trimming moment is zero. The “free to trim” method is representative of how the vessel will behave, allowing the vessel to trim until the trimming moment is zero, with no restrictions on draft or trim. The use of the fixed trim method originally simplified the calculations performed by naval architects and produced accurate results for traditional model bow tugboats that were predominant. However, as tug styles and computers have evolved, the methodology is no longer as relevant or necessary.
The paper quantifies what affect the fixed trim method has on the calculated righting energy at large angles of heel and determines when the method is no longer valid. The analysis looks at tugboats currently in operation representing a range of design characteristics and ages. The results show that the fixed trim method may provide a reasonably accurate righting arm curve for traditional model bow tugboats in some loading conditions. However, the fixed trim method can result in unrealistic and exaggerated righting arm curves for many foc’sle bow tugboat designs, particularly in the intermediate and load line conditions. As older tugs are modified and new design trends evolve, it is important that naval architects understand the underlying reasoning behind the regulations that are applied to these vessels.
U.S. Navy Salvor’s Handbook
$30.00Released by the Navy in 2006 to replace the 1990 version. 242 pages, pocket-sized soft cover.
An abridged version of the 6 volume U.S. Navy Salvage Manual Series. The book is designed as a ready-reference to be taken along to the salvage site and is conveniently sized to fit in the hip pocket.
U.S. Navy Underwater Cutting and Welding Manual
$95.00164 pages, 3-ring binder.
This manual incorporates the U.S. Navy’s state of the art equipment and tried and proven underwater cutting and welding techniques. It is a collection of Navy fleet and commercial experience and has been reviewed by technical experts with extensive salvage and underwater cutting and welding experience. It is the most current information on equipment and procedures available.
U.S. Navy Towing Manual
$110.00301 pages, 3-ring binder.
This manual supersedes the May 1987 edition in its entirety and all other towing manuals. Various towing manuals have attempted to go beyond the cookbook type approach of providing detailed information for accomplishing one or at most a few specific kinds of towing missions. This manual includes the full spectrum of Navy towing and provides the user an improved feel for the logic behind the recommendations and guidance. This manual completes previously incomplete appendices by providing more consistent format and graphics work and by including the results of recent R&D efforts to estimate peak towline loads in varying sea states.
U.S. Navy Ship Salvage Manual Vol. 1 [Standings and Harbor Clearance]
$110.00Released by the Navy in 2008 to replace the 1990 versions of Vol 1 & 2. 398 pages, 3-ring binder.
This volume focuses on strandings and provides expanded material on the application of naval architecture to marine salvage. The naval architecture chapters are background for all the volumes. An understanding of salvage naval architecture is vital to salvors’ understanding of how a ship will respond in situations for each she was not designed. All calculations are presented so they may be made by salvors in the classroom or in the field with only a hand-held calculator.
This volume also focuses on the salvage of sunken ships, and in a broader sense, harbor clearance, where actual ship salvage is secondary to obstacle or wreck removal. It presents practical information to the Navy salvor conducting sunken ship salvage or harbor clearance operations, and incorporates specific techniques previously employed to solve real problems associated with actual wreck removal operations. Organizational relationships, both external to and within the Navy, are defined to assist the salvor in planning during major salvage operations in periods of hostilities or in the wake of natural disasters. Appendices containing technical information about U.S. Navy salvage equipment, commercial equivalents of many standard stock items, innovative tools, and environmental effect of extreme cold weather operations have also been included for ready reference to the Navy Salvor.
U.S. Navy Ship Salvage Manual Vol. 4 [Deep Ocean]
$95.0068 pages, 3-ring binder.
Salvage of objects from the seafloor has been a major technical challenge for many years. The U.S. Navy has acquired extensive experience through cumulative research and development, both at naval and commercial laboratories. Long days at sea combining both new technology and seamanship have developed the world’s best deep ocean search and recovery capability. This manual addresses principles and methods of deep ocean recovery. It is intended to serve as a guide for shipboard and deep ocean recovery personnel.
U.S. Navy Ship Salvage Manual Vol. 5 [Emergency Petroleum Offload]
$95.00148 pages, 3-ring binder.
The increasing importance of preventing pollution at sea, and the large quantities of oil carried in ships has made emergency petroleum transfers an important part of salvage operations. Because of the nature of the material being transferred, petroleum operations are inherently dangerous. This volume describes procedures for removing oil from the fuel systems of casualties and for the special and complex task of removal of cargo oil from tankers and replenishment ships. Salvors must be aware that the latter is not a routine matter of “flanging up and pumping.” Salvage transfers require extensive planning, a high level of technical competence and good seamanship by salvors. Appendices containing technical data on petroleum transfer equipment and transfer checklists complement the text.
U.S. Navy Ship Salvage Manual Vol. 6 [Oil Spill Response]
$95.00202 pages, 3-ring binder.
Having accepted responsibility for a casualty, salvors are expected to endeavor to stop or reduce spillage in progress, to conduct salvage in a manner that minimizes the risk of further spillage, and to respond to spills that occur as a result of salvage work. This volume provides guidance to the salvor facing a major pollution incident resulting from a ship stranding, sinking, fire, collision or explosion. This volume is intended for use by all personnel who may be tasked to participate in oil spill response or contingency planning. Salvage and spill response efforts often proceed simultaneously, and may either complement or conflict with one another. Only a thorough knowledge of the methods and requirements of both efforts can ensure a smooth, successful operation.
U.S. Navy Salvor’s Handbook ver 5.0
This version includes 12 easy-to-use calculators based on the most popular formulas in the US Navy Salvor’s Handbook!
– Estimate Bollard Pull
– Hydrostatic Pressure
– Flooding Rate
– Moment to Trim One Inch
– Shaft Diameter
– Tons per Inch Immersion (TPI)
– GM from Roll Period
– Freeing Force
– Ground Reaction
– Patch Thickness
– Change in Draft
– Current Force
