Military

June 2002 Excerpt

Mooring the Fleet Around the World

By Lou DiStefano

PHILADELPHIA—The Code 97 Anchor, Mooring, and Towing Team is frequently tasked to provide equipment and procedures for the design of mooring DoD vessels. Mooring is defined as a compliant structure that restrains a vessel against the action of wind, wave, and current forces. The emphasis is on moorings composed of tension members (chain, line, wire rope, etc.) and compression members (fenders, camels, etc.) used to secure vessels.

The primary emphasis of the Anchor, Mooring, and Towing Team is the mooring of floating structures or vessels, such as ships, yard craft, submarines, and floating drydocks in harbors. The Code 97 team must also address systems where the environmental forces on the mooring members themselves are important, as may be the case for towed underwater bodies, ship-to-ship at-sea mooring, and towing of one vessel by another.

This team has a long history of mooring vessels in harbors throughout the world. This experience has shown the ability to analyze moorings according to a set of common and well understood basic principles. This is critical for safe and cost effective mooring operations. They also developed procedures for the evaluation and design of mooring facilities for DoD vessels, which is intended to provide guidance to users, operators, and designers of mooring facilities for DoD vessels. The various mooring systems are designed to withstand forces and moments generated by winds, waves, and currents acting upon the vessel, as well as environmental and operational requirements that are unique at each site and to each vessel.

The Anchor, Mooring, and Towing Team has developed a database of various mooring arrangements utilizing numerous fender designs. Most of the information was gathered from feedback on “lessons learned” from past DoD mooring operations, as well as new technology and procedures for mooring analysis which have been developed in both the commercial and government sectors. The illustration above demonstrates one of the various arrangements required to safely moor a ship (CVN) to a pier utilizing camels.

The team takes a basic design approach when developing a mooring arrangement. We begin the design with specified parameters and use engineering principles to complete the design. The types of parameters associated with these mooring projects include:

• Ship position.
  
  
• Amount of motion allowed.
  
  
• Length, width, draft, and displacement.
  
  
• Wind areas.
  
  
• Mooring fitting locations.
  
  
• Wind/current force.
  
  
• Moment coefficients.
  
  
• Facility configuration, location, condition, and overall capacity.
  
  
• Water depth.
  
  
• Locations/type/capacity of mooring fittings.
  
  
• Environmental parameters such as wind speed, current speed, direction, water levels, wave conditions, the possibility of ice, and material properties of the fenders (stretch/strain characteristics).