Mid-July
2005
Table
of Contents:
Chesapeake Section |
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Pacific Northwest Section |
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Mid-July
2005
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Chesapeake
Section May 18, 2005 NATO:
design of offshore patrol vessels and small combatants On May 18th thirty-three members and guests attended a SNAME Chesapeake Section dinner meeting held at the U.S. Coast Guard Yard in Baltimore, MD. The evening’s events included a presentation by Mr. Christopher Cleary of the U.S. Coast Guard. Mr. Cleary is a Senior Naval Architect with the Engineering Logistics Center (ELC) of the U.S. Coast Guard and has served as Chairman of a NATO Specialist Team on Small Ship Design. Mr. Cleary’s presentation summarized the findings and recommendations of a working paper developed by this NATO specialist team on “Offshore Patrol Vessels and Small Combatants - International Technology and Design Practices”. The author noted that this working paper was developed by NATO to investigate acceptable criteria, standards and specifications for the design and construction of small littoral combatants and offshore patrol vessels with displacements of approximately 600 tons to 2000 tons. He also noted that a secondary purpose of chartering this team, beyond development of the working paper, was to acquire and spread new information on technology and materials suitable for small ships and stimulate new thinking in small ship acquisition programs between the nineteen NATO and Partner for Peace Nations that were involved in its development.
The
paper addressed eleven major areas, including the following: manning,
mission modularity, power generation and propulsion, marine environmental
protection, replenishment at sea, helicopter/small boat/ and unmanned-aerial-vehicle
launch and recovery, advanced hull forms, composites, signatures management,
vulnerability reduction, and total ownership costs. A full copy of this
working paper is available at – The members were pleased with the strong turn out at the new venue, and therefore can expect another meeting to be hosted again next year by the naval architects at the ELC. In addition, members have also expressed keen interest for a short yard visit next year. The Chesapeake Section is looking forward to renewed activity in the Baltimore sub-section.
June 15, 2005 Aerostats – effective platforms, but suffer from lack of technical advances Over thirty members and guests, including visitors from the Southeast and Texas Sections, attended the June 15th lunch meeting that featured a presentation by Dr. Pramud Rawat on the history and development of aerostats. He has been dealing with aerostat designs for the past fifteen years. Aerostats are light-than-air (helium-filled) tethered balloons. The larger sizes can fly at up to 15,000 feet and carry surveillance radar in a pressurized streamlined compartment. Smaller versions of aerostats fly from winches mounted on ships or on towed trailers. They are also generally used for surveillance purposes and for carrying communications or sometimes even advertising payloads.
Research and development of aerostat design has lagged behind most other vehicles for several reasons. The most apparent of these is that aerostats are unmanned and relatively inexpensive. However, Dr. Rawat proposed that this lack of interest should be re-assessed since aerostats can provide a key platform for several purposes. For example, in 1990 in Kuwait, an aerostat-mounted radar detected the approach of the Iraqi army. After Dr. Rawat briefly reviewed that status of current aerostat design, he described the major problem areas in design refinement. These involve the proper characterization of turbulent weather, which a stationary aerostat cannot avoid as can other aircraft, and proper analysis of an aerostat’s behavior in bad weather – problems as complex as motion prediction of offshore platforms in a heavy sea. Unfortunately, a lack of funding for testing or collection of environmental data frustrates the ability to study aerostat major failure modes using small deflection theory. However, because modern mathematical simulation tools of complex engineering systems are more economically available, Dr. Rawat believes that new analysis of aerostat problems involving coupled forcing functions and nonlinear responses are worthwhile.
Pacific
Northwest Section June 9, 2005 The June technical meeting took place at 5:30 PM on Thursday, June 9, 2005 at the Olympia Lodge of the US Naval Station, Bremerton, WA. It was also the annual joint meeting with the American Society of Naval Engineers [ASNE]. Approximately 30 people attended the meeting. After dinner, SNAME member Stan Stumbo gave a presentation titled “What’s Being Done About Wake Wash?” Mr. Stumbo is an independent marine transportation consultant with special expertise in wake wash matters, including wash measurement and analysis. Mr. Stumbo began with a brief overview of the current practice of wake wash data gathering. Although 14 variables could be collected from field measurements, the maximum wave height and energy (proportional to wave heights and periods) measured at a specified distance from the vessel’s course are often cited for comparison purpose. The de facto standard distance is 300 meters. Data of the complete wave train is often captured for use in other analyses. Vessel trials usually take one day, with instruments deployed at one location. The ambient data can often be extracted from NOAA weather records for wind and waves. The recent wake wash measurement that involved trial runs of the M/V Spirit in Puget Sound was explained in depth. The Spirit was used as the reference vessel in order to select the preferred characteristics of a suitable vessel for high-speed service through the Rich Passage. Typically, wake measurements in deep water are useful for comparing the wake wash characteristics of different vessels, whereas wake measurements in shallow water are only useful in studying the potential impact along a specific route. Because ‘conventional wisdom’ equates all high-speed vessels with excessive wave-making, wake wash studies have become essential parts of high-speed ferry programs. The objective of such a study is to collect data and to establish technical support to quickly and effectively quash the ‘data-free’ analysis of critics and complainers. A typical wake wash study may include the collection of data along the intended route, the prediction of wake wash impact of a new vessel, the determination of desired hull characteristics in terms of wake wash, and the verification of wake impact at a vessel’s sea trials. Mr. Stumbo cited recent studies commissioned by the Alaska Marine Highway System [AMHS], San Francisco’s Water Transport Authority [WTA] and other authorities. In the first case, AMHS’s study established with confidence that its new high-speed vehicle ferry (M/V Fairweather) will generate a lower wake wash profile than the existing cruise ship and ferry traffic on the intended service route. In WTA’s case, studies identified several wake-sensitive areas, along with the findings that vessel-generated wake wash will not exceed the wind-generated ‘background’ waves along some routes in San Francisco Bay. According to Mr. Stumbo, other areas where wake wash is an issue include Mobile Bay in Alabama, Rich Passage in Washington, New York Harbor in the USA, Halifax Harbor in Canada, Marlborough Sound in New Zealand and certain areas in Ireland. The presentation was followed by lively discussions.
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