Navy ships have been designed and operated for the past 50 years in accordance with empirically based stability criteria which were derived for wall-sided and flared monohull vessels of World War II vintage.
Existing ship stability criteria do not adequately address dynamic stability, nor the stochastic nature of the wave environment. These criteria are typically based on hydrostatics and include margins, which are only approximate means of accounting for ship dynamics. The stability criteria do not account for a ship’s dynamic behaviour in extreme seas. Even modern hull forms may experience large roll angles in extreme sea conditions.
As warships must be able to operate in high sea states and at high speeds, this problem is of particular concern to navies. Stability requirements can have a major impact on decisions made during the design of these ships, such as the location of the center of gravity. In addition, such criteria dictate the inherent levels of safety against capsizing. Therefore, there is a clear need to develop dynamic stability criteria for practical design purposes on a rational basis.
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Participants contribute their expertise and technology to the group's research efforts. MARIN provides the CRNAV chairmanship and secretariat, as well as overall project management.
The Cooperative Research Navies (CRNAV) started in 1989 with the intention to investigate the dynamic stability of naval vessels. The main activities comprise the following areas:
Participating Navies have formed the Naval Ship Stability Working Group (NSSWG) to develop more rational based dynamic stability criteria than presently available. The Operator Guidance Training & Working Group (OGTWG) was formed to include operational information in capsize risk assessment studies and to further introduce heavy weather training on bridge simulators linked to FREDYN.
In principle the research is carried out by the member organizations only. The results of the investigations are the sole property of the CRNAV members. The strictest confidentiality is maintained and results may be published only after approval of the CRNAV. Each organization may decide to continue the cooperation or to withdraw at the conclusion of each three-year period. Overhead costs are kept to a minimum.
The research program of CRNAV is broadly defined for three year periods (phases) and closely defined for each coming calendar year. The work includes Fundamental, Design, and Operations oriented projects. Fundamental work deals with the further development and validation of FREDYN for prediction of extreme motions for intact and damaged ships. Design orientated work focuses on capsize risk assessment of intact and damaged ships, while Operations oriented projects deal with operational guidance and training.
The CRNAV group consists of the following members (2015-2017 period) with voting rights:
The CRNAV group further consists of the following associated members (2015-2017 period):
In principle all organisations interested in the design and operation of naval ships may become member of the CRNAV. However, new members are accepted only by unanimous agreement of the existing members.
The NSSWG was established in 1999 as a sister group to the CRNAV. Its membership consists of representatives from a number of Navies. They are supported by guest members from associated research organisations. This group is not directly funded but is supported by the CRNAV group as such membership is limited to full members of the CRNAV.
The objective is to develop a shared view on the future of naval stability assessment and develop a draft set of stability guidelines which can be utilised by the participating navies at their discretion.’
This working group is considering the following issues:
This working group consists of the following members:
The current guidelines for ship handling in severe seaway conditions are based on practical knowledge and rules of thumb attained over decades of experience with conventional naval ships. While this has worked in the past to ensure that correct ship handling decisions are made while in severe seaway conditions, at sea time and resultant practical ship handling opportunities for watch officers are diminishing in today’s navies. There is a heightened need to explore and develop new methodologies for training of watch officers, CO’s and XO’s in ship handling in the severe seaway environment. In addition, recent simulation studies have shown that some traditional guidance may actually put ships at increased risk of capsize. The Operator Guidance, and Training Working Group has been formed to examine these issues and develop a shared perspective for reference by member navies in addressing training, technology and operator guidance needed to manage the risk of capsize at sea.
The OGTWG aims to develop a shared view on the future of naval stability operator guidance and training for severe seaway conditions. The group is to develop a draft set of Naval Stability Operator Guidance and Training guidelines which can be utilised by the participating navies at their discretion.
The OGTWG is considering the following working points:
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