Company: Waterweights Makes Light Work of Heavy Lifts

The Water Weights division of Imes Inc., under contract with NASSCO (National Steel And Shipbuilding Co.) and in partnership with JW Automarine recently achieved a first in the innovative use of Air Lift Bags to assist in float-out of a vessel from dry-dock. The project was also the largest lift achieved by JW Automarine using this type of bag.

NASSCO of San Diego has been designing and building ships since 1960, specializing in auxiliary and support ships for the U.S. Navy as well as oil tankers and dry cargo carriers for commercial markets. Most recent on their long resume of new builds would be 2 Orca Class roll-on, roll-off (RO/RO) trailer ships for TOTE (Totem Ocean Trailer Express, Inc.). It is to assist with the float-out of these ships that the innovative and cost efficient idea was hatched.

Originally, the NAASCO dry dock was designed for the building and servicing of Super Tankers of 200,000-ton capacity. The draft requirements for these vessels were quite small due to their light ship weight and design, therefore when Nassco was called on to build two of the trailer ships; the draft exceeded the maximum depth possible in the dry dock. The solution after extensive examination was to reduce the draft by fitting underwater lifting bags on the vessel.

The plan involved the fitting of lift bags, each unit having a displacement lift of thirty-five metric tons. Malcolm Felmingham from JW Automarine's "Weight Lifters" team was onsite offering a wealth of advice and assistance. The JW Automarine team's reputation in practical manufacturing, deployment experience and competence with lift bags is without equal worldwide.

After extensive planning and development, rigging of the bags and trials commenced. When everything was deemed safe, trials concluded, and the actual lift took place to coincide with the most suitable tide. The bags were kept continuously monitored and regulated from on board compressors controlled via a 40-valve manifold system by the team. Once the tide height was sufficient for the vessel to lift off the blocks the float-out was successfully achieved. We are very proud of the way challenges are approached by our team and partners, says Imes Inc. President Robin Baxter, "Our Company's goal has always been the provision of innovative solutions to meet our client's requirements worldwide, and we feel we've achieved that with this project".