NASSCO, San Diego, CA
Dry Dock No. 1

See More Caisson Gate Design

NASSCO’s Dry Dock No. 1 is a basin type dry dock that was originally constructed in 1976 for the purpose of building and launching large vessels. The basin dock is approximately 1,000-ft long by 180-ft wide and utilizes a floating type enclosure gate at the entrance of the dock. Since 1979, the dock has been certified by NAVSEA and currently has a capacity for supporting vessels displacing up to 76,000 long tons.

In 2018, NASSCO tasked HEGER DRY DOCK INC with designing a replacement gate for the facility. HEGER engineers were tasked with modernizing and improving the original gate design. Improvements included a more robust steel structure capable of withstanding an earthquake with an expectancy of once in every 2,500 years, a reversible type design so maintenance could be performed more easily, a customized gasket seal design to ensure proper sealing during all tidal cycles, etc.

As part of the hull design, HEGER created a comprehensive 3D computer model of the gate structure for Finite Element Analysis (FEA). The computer model was utilized to verify adequacy of the structural system in support of all design load combinations and evaluate the performance of various perimeter gaskets to ensure the highest quality product was developed prior to construction.

Caisson Gate NASSCO Dry Dock 1 - finite element analysis of structural hull
Figure 1 – FEA Evaluation of Structural Hull
FEA evaluation of perimeter gasket - NASSCO Dry Dock 1
Figure 2 – FEA Evaluation of Perimeter Gasket
Aerial View of Caisson Gate Dry Dock 1 NASSCO San Diego CA
Figure 3 – Aerial View of Gate

On this project, HEGER partnered with an industry expert in APPLEDORE MARINE ENGINEERING, LLC of Portsmouth, New Hampshire to perform all engineering which related to landside elements of the facility.

The caisson gate was constructed onsite at NASSCO’s facility in San Diego, CA with HEGER providing continuous engineering support during the construction phase of the project.

Ultimately, the new gate was successfully commissioned in 2020.

HEGER continues to provides ongoing engineering support with routine maintenance inspections.

Basin Dock Floods Through the Caisson Gate
Figure 4 – Basin Dock Floods Through the Caisson Gate
NASSCO Dry Dock No 1 replacement gate being lifted into place by crande
Figure 5 – Gate Designed to be Lifted by Yard Cranes
Portsmouth Naval Shipyard, Kittery, ME
Dry Dock No. 2