The dredge tender Ivanoff was built to maneuver the Port of Portland’s dredge Oregon along the sites it dredges on the Columbia and Willamette rivers, working to maintain important navigation channels. The Ivanoff was lacking in propulsion and steerage both ahead and astern to meet the Port’s operational needs. Despite having more power, the Ivanoff was routinely outperformed by the Port’s other dredge tender, the Clackamas. As a qualitative test, the Port chose to perform a push test between the Ivanoff and the Clackamas, which the Clackamas handily won.
Understanding an Underperforming Vessel
In 2015, the Port of Portland commissioned Glosten to investigate design improvements to the Ivanoff. Glosten deduced that the Ivanoff’s performance issues were related to the stern hull shape, rudder configuration, and propeller sizing. After discussions with the Port, it was determined that the best solution would be to completely redesign the vessel’s stern and propulsion system, with the goal of enabling the Ivanoff to perform the necessary dredge handling operations.
Analyses and Comparisons
A qualitative baseline for comparison of the Ivanoff’s new stern hull design was accomplished by computational fluid dynamics (CFD) analyses using 3D computer models of the original Ivanoff hull and the Clackamas hull. These analyses provided quantifiable metrics that showed the Clackamas hull was superior to the original Ivanoff hull, matching the real-world results of the push test. Glosten then designed a new Ivanoff hull and modeled the design to compare with the Clackamas. The analysis showed a significant improvement over both the original Ivanoff and Clackamas hulls. Additional design work was done to change the vessel’s drive gear reductions, propellers, and rudders to facilitate the Port of Portland’s desired performance improvements.
The Ivanoff began its transformation in early 2016. The selected shipyard, JT Marine, hired Glosten’s Production Services team to provide detail design for the retrofit. Since leaving the yard, a bollard pull test confirmed that the newly-modified Ivanoff exceeds the bollard pull of its old design by 29%, as well as exceeding that of the Clackamas.
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