Side cast dredge Monarch at its lay-up location

Project Summary

After sinking and re-floating, an old side cast dredge needed to be removed from its lay-up location in Shag Slough, part of the Sacramento river delta. The dredge had a riveted iron hull with a wooden bottom. Since a wet tow to the demolition location at Mare Island was considered too risky, NRC Environmental Services proposed a dry tow solution. By putting the dredge onto a cargo barge, the probability of sinking and causing pollution was eliminated. A suitable cargo barge was location in Seattle and towed to Alameda for preparations. Stand pipes with submersible pumps were installed on four of its ballast tanks. A cribbing arrangement, guideposts, protection posts and  boom support were installed. Meanwhile the dredge was prepared for its final tow.

On February 26, 2004, the cargo barge MZB 287 arrived on the loading location and was ballasted down until it rested on the bottom, with sufficient water over deck to allow for positioning the dredge over its cribbing. Next day, the dredge was carefully maneuvered over the submersed barge and positioned against the guideposts. By deballasting the barge in accordance with the deballast procedures, the dredge was safely lifted out of the water, while maintaining positive stability. Once the towing condition was reached, the barge was towed to the demolition contractor at Mare Island, only 40 miles down river, making this the shortest dry tow Argonautics Marine Engineering was ever involved with...  

Scope of Work

The project scope included:

• Verify feasibility of selected non-submersible cargo barge;

• Design detailed ballast procedures for safe sinking and re-floating of the barge;

• Design cribbing arrangement;

• Design positioning guideposts and stand pipe protection posts;

• Design boom support;

• Provide on-site assistance during actual loading operation.

Acknowledgement

Photographs courtesy of Foss Maritime.

Project Photographs

Maneuvering the dredge towards the submersed barge.	Barge deck coming out of water.	Boom tip is removed with a floating crane.	Dredge being demolished on cargo barge.