Submersible patroller is seakindly and stable PATROL VESSELS
Center (NSWC) explained at a recent conference, recent gains in hullform design have enhanced the seakeeping ability of small types of combatants such as patrol boats. Exploiting these gains, the NSWC and Naval
A
Sea Systems Command (NAVSEA) have been working together with shipbuilder Oregon Iron Works on the design and construction of a 71ft Technology Demonstrator, designed to be more seakindly and stable than earlier craft – and have the added advantage of being submersible. The craft is known as Sealion. Sealion was designed to have improved
seakeeping characteristics and reduced hull motions in a seaway, compared with other US Navy vessels, which, the NSWC and NAVSEA anticipate, will result in reduced fatigue and injury experienced by personnel during training and operations. The Sealion Technology Demonstrator was
delivered for evaluation in January 2003 and is currently the subject of what the US Navy describes as ‘operational experimentation.’ Apart from offering a particularly stable design
with good seakeeping for maximum logistical flexibility – it can be carried onboard C-17 and C-5 aircraft and on conventional Maritime Sealift Command and US Navy vessels. Sealion will help the US Navy with a range
of technologies for advanced high-speed craft, including hullforms, structural design and construction, propulsion, systems design, electronics, and Human System Integration (HSI), plus areas such as mission integration and modular reconfiguration. As Ms Grimsley Speirs explained, the need
for advanced technology craft in the US Navy is expanding. Current generation craft are expected to perform a range of missions, such as maritime interdiction operations (MIO), border protection, and personnel transport for anti-terrorism and force protection, but the shortcomings of these platforms are becoming apparent. Existing craft and new ones are required to
maintain high speeds in heavy seaways with no injury or degradation of the performance of personnel and without damage to the craft, its equipment, or its payload. ‘The reality is that current craft are injuring crew members at a rate nearly six times that of the overall US Navy average,’ Ms Grimsley Speirs explained, ‘and
S Jenny Grimsley Speirs of the Carderock Division of the Naval Surface Warfare
The Sealion concept is intended as a seakindly, stable semi-submersible craft.
the craft are suffering increased maintenance costs due to operations at speeds and acceleration levels beyond the craft design.’ The missions that patrol boats and small
craft are required to carry out are becoming more complex and require the gathering and transmission of much greater amounts of information, which places heavy demands on existing craft for Command, Control, Communications, Computers, and Intelligence (C4I) equipment. Another important requirement is the ability to rapidly reconfigure a vessel to suit a range of missions. ‘The requirement to process increased
amounts of information for use by the crew and the extended duration of many of the missions require designers to ensure that human systems interface issues are being addressed, and, finally, the need to maintain presence in the battle space (either at home or abroad) often entails the craft getting to theatre quickly and operating undetected, requiring the designer to address and resolve issues related to craft signatures,’ explained Ms Grimsley Speirs. Recognising shortcomings in existing patrol
craft, the US Navy identified the need to focus on a number of key areas. These are:
TECHNICAL PARTICULARS SEALION
Length, oa ......................................... 71ft Beam .............................................. 14.3ft Displacement ................................... 30LT Speed ....................... - in excess 40knots Range ......................................... 300+nm Payload ......................................... 5000lb Minimum draft ................................... 3.4ft Maximum draft .................................. 4.7ft
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• Hullform. • Structural design and construction. • Propulsion and systems design. • Electronics and weapons integration. • Human systems integration. • Mission needs integration. • Modular reconfiguration.
At about the same time that the US Navy
began working on Sealion, it came to the project team’s notice than another navy was also
Sealion was designed to have improved seakeeping characteristics and reduced hull motions in a seaway, compared with other US Navy vessels.
investigating technology areas to meet similar craft requirements, and that a 65ft technology demonstrator craft, known as Alligator, was under construction at Oregon Iron Works. With a length overall of 65ft and beam of
13.4ft, this craft was intended as a high-speed, semi-submersible combatant with improved seakeeping characteristics. It was to have a displacement of 23tonnes, speed of 40knots, range of 500nm and maximum draft of 4.55ft. A team from the NSWC conducted trials on
Alligator craft prior to its delivery and met with the vessel’s engineers and operators to discuss the design of the craft and lessons learned. Based on the capabilities demonstrated by the vessel during tests, and feedback received during the visit, the US also decided to explore the concept of a semi-submersible hullform with good seakeeping characteristics, but with modifications to suit US requirements.
WARSHIP TECHNOLOGY MAY 2007
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