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NEWS | Oct. 17, 2019

PSNS & IMF builds 51 cofferdams to increase ease of use, reduce cost

By Max Maxfield, PSNS & IMF Public Affairs

When workers at Puget Sound Naval Shipyard & Intermediate Maintenance Facility need to test or perform work on certain valves or other ship’s components when a ship or submarine is pier side, they use cofferdams to create a dry space around where that valve or other component meets the sea. Divers attach the cofferdams on specific parts of a ship and pump the water out of them. This allows the valves to be opened up and tested without risking flooding to the ship.

According to Fredianne Gray, an engineering technician with Code 250.1, Surface Ship Structural Branch, the   large cofferdams used until recently were designed in 2007 by Paul Raadt, from Code 250, Structural Engineering and Planning. 

The recently built cofferdams incorporated a redesign by Adam Spahn, a naval architect with Code 250.6, Naval Architecture Branch, who collaborated with John Fontenot, a branch manager with Code 280, Planning Yard.

Reliability, design executability and cost savings all factored in to the decision to return to designing and building cofferdams at PSNS & IMF, said Gray.

People from across multiple shops and codes worked through a variety of design and manufacturing challenges to produce top-quality cofferdams that are easier to use than the older ones were.

By using a PSNS-owned drawing, the command’s shipfitters and welders were able to come up with an expedient process to manufacture cofferdams that reduces rework and improves workflow, said John Fahey, a general foreman with Shop 11/17, Shipfitters/Sheet Metal. Cofferdams are customized for specific valves, and range in size from 16 inches to 16 feet across. Since they are aluminum, a soft material, they require tightly controlled shipfitting and welding processes.

Aluminum is much more difficult to weld than steel because it distorts at a lower temperature.

“The fitters worked through issues requiring weld size and joint design changes, work sequencing, complex back-stepping and heat sink use,” said John Tibbs, a supervisor in Shop 11, Shipfitters. “Flange turning processes using presses and flame straightening were especially critical during and    after welding to compensate and overcome for what the heat controls couldn’t accomplish.”

Tibbs acknowledged the skills of shipfitters Wes Doane, Jeremy Boyd and Fred McFarlane; flange turners Pat Cartwright and Steve Preas; and welders Terry Daniels, Luke Feist, Tran Anderson and Jake Skinner in successfully producing the cofferdams.

According to Dan Downard, a supervisor in Shop 26, Welders, two experienced welders, Luke Feist and Richard Knight, volunteered to work swing shift to weld cofferdams to help the team meet the scheduled finish date.

The team that took on the challenge of fabricating cofferdams at PSNS & IMF not only to replace an aging inventory in a cost-effective manner, but also to improve upon the design and make them easier to install.

“PSNS-designed large cofferdams incorporate void spaces that can be filled by the divers with variable volumes of water or air to help the cofferdam sink during installation or become more buoyant during removal,” said Gray. “In addition, there are two new removable, bolt-on plates on the top of the cofferdam which allow it to be opened up.  These plates allow the inside of the cofferdam’s chambers to be cleaned and inspected, which will considerably lengthen its service life.”

Meeting the divers’ buoyancy needs  required field testing of the cofferdam gasket material by the divers.

During the design of this new cofferdam, J.P. Kunewa, the production general foreman, diving, with Code 760, Regional Divers, conducted a buoyancy test, where he took different gasket materials from the surface of the water down to a depth of 56 feet and measured the force of buoyancy on those materials at different depths, said Spahn. As the gasket material was taken deeper, it became more compressed and less buoyant. The compression and change in buoyancy of the gasket was taken into account in the design of the cofferdam to make it easier for the divers to use underwater.

Through a collaborative effort among Shops 11, 26, and Codes 250.1, 300, and 760, and with innovations and process improvements, PSNS & IMF has been able to fabricate 51 cofferdams this year. 

Gray said completing just one cofferdam takes an enormous amount of skill and perseverance. Meeting all the challenges involved in completing 51 cofferdams in a year is a credit to the skill, professionalism and dedication of the entire team.