Retrofitting an Existing Berth for Heavy Weather Mooring Conditions

Abstract: The Massachusetts Maritime Academy (MMA) was selected to participate in the National Security Multi-Mission Vessels (NSMV) program by MARAD. MARAD provides the training ships used by the State Maritime Academies and the NSMV program plans to upgrade five training vessels. The program was created to address the aging training fleet and to provide versatile training and disaster response vessels. The new ships provide state of the art training facilities and disaster response capabilities. With this multi-mission capability, MARAD required the academies to provide dock facilities with heavy weather mooring capacity for Category 1 hurricane conditions. The new NSMV ship has similar dimensions to the previous MMA training ship but is slightly wider and has much larger lateral wind area. Initial analysis of the MMA dock by MARAD found that the existing structure and mooring and berthing equipment was unlikely to have adequate strength to support the heavy weather mooring conditions.
The dock had been recently inspected and found to be in overall good condition and MMA was seeking to evaluate means to upgrade the existing dock without complete replacement. The site is in an exposed location at the southern end of the Cape Cod Canal. It has significant exposure to the southwest and is located close to the canal which has strong tidal currents. The site is also constrained by shoals to the southwest which, combined with the wider ship, limited any significant shifting of the berth further offshore. A solution was required which maintained the existing berth alignment but upgraded the mooring bollards and fenders. MARAD had indicated that most of the mooring bollards should be upgraded to 200 metric ton capacity with one bollard at 250 metric ton capacity.
Static and dynamic mooring analysis was performed for the new ship to evaluate previous work, to confirm bollard locations and to develop mooring line loads and fender performance parameters. Fender performance criteria were critical with relatively low allowable hull pressure and the need to limit the magnitude of loading on the existing structure. Dynamic mooring simulations were performed for a range of metocean conditions and for the full 360° range of possible wind directions. Special attention was paid to create a gust spectrum consistent with ASCE 7-16 criteria, which results in more gustiness than in standard operational winds over water. An emergency mooring arrangement was created with doubled-up mooring lines connected to bitts on the vessel avoiding possible slipping of the winch brake. Berthing energy calculations were also performed and confirmed that mooring conditions govern for the fender selection.
The dock structure was analyzed for the new bollard loads and found to be inadequate for the higher loads. A retrofit was designed adding additional piles and a stabilization beam at the outshore edge of the existing structure. The new piles in the retrofit were installed with tension sockets to brace the existing structure. The new and existing structures were analyzed and designed as a composite structure capable of supporting the higher loading.

How does this project / topic contribute to the advancement of the industry and profession?: This project solved a complex mooring problem and allowed retrofitting of an existing facility for more severe weather conditions. This approach is already becoming essential to address climate change impacts.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: This project utilized dynamic mooring analysis to establish both mooring line loading and fender specification requirements. Fender selection was crucial to allow adequate range while limiting loading on the existing dock structure.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The most challenging aspect was creating a mooring line layout which could meet the specified design requirements while working within the limitations of the vessel equipment. An emergency mooring arrangement was created with doubled-up mooring lines connected to bitts on the vessel avoiding possible slipping of the winch.

Who is the target audience for this paper?: Port managers interested in upgrading existing facilities and designers looking for potential analysis and design solutions