Watertight doors and watertight hatches are critical components of a Navy vessel’s function and safety, allowing for safe passageways for servicemen and women throughout the ship.
These heavy-duty doors and hatches need to be manufactured to exacting specifications in compliance with NAVSEA standards and must pass rigorous testing.
This article will help Department of Defense contractors and procurement specialists understand the critical role that a custom metal fabricator plays in producing these components and why not every company is up to the task.
First, let’s clarify what we mean by watertight doors and hatches.
When referring to passageways on a ship, many will use the terms “doors and hatches” synonymously. While they serve similar purposes, there is a distinction.
Watertight doors are special types of doors on naval vessels that allow for horizontal passage from one compartment to another while also preventing the ingress of water.
Similar to watertight doors, watertight hatches prevent water from entering a compartment. However, hatches allow for vertical passage between different decks of a ship.
It should be pointed out that there is also a difference between watertight and weathertight. A watertight door or hatch is installed below the waterline in shafts, tunnels, ballast tanks, and other compartments. Watertight doors and hatches can withstand water pressure from both sides in the event of an accident or flooding and ensure that water cannot enter a compartment.
On the other hand, weathertight doors and hatches are located above the waterline and prevent entry of water under normal sea conditions or inclement weather. They are not intended to prevent the entry of water under high pressure or in the event of an accident.
One of the first considerations when choosing a metal fabrication company to perform work for the Department of Defense is ensuring they have AWS and NAVSEA certified welders, and that they’ve successfully performed work for the military in the past.
Fabricating watertight doors and hatches comes with unique challenges that some metal fabrication shops may not be equipped to tackle. When deciding which fabricator to include in your RFP process, also consider the following:
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One factor is simply the space and equipment needed to produce and move these structures. Some door units may span a few feet whereas others may span 12–20 feet, as is the case for sliding transom doors used on some ships. These units can weigh several tons. Maneuvering these massive structures requires overhead cranes, forklifts, and reinforced structural capabilities. Likewise, a facility needs adequate space and capacity to house the units. Size limitations alone can limit which metal fabrication company can take on the work.
Achieving the complexity and precision required to manufacture watertight doors and hatches will not be accomplished by amateur welders. Highly skilled, certified welders who work on defense projects have years of experience and training. They must be able to work with numerous materials and understand how each performs under different conditions. They must also abide by approved welding procedures for various material types and thicknesses.
Watertight doors and hatches are most often made of carbon steel and their structural skeletons might be engineered using i-beams or other structural shapes and heavier plate materials. The face surface is generally 1/2 to 5/8-inch thick depending on application and includes a web of internal components. When you add it all up, a door unit could be 20-inches thick depending on its application. Such complex structures require the use of multiple jigs and fixtures, and the welding capabilities to achieve tight tolerances.
Among the greatest difficulties in fabricating large doors and hatches is ensuring flatness, especially along the sealing surface and where operating mechanisms are attached. The way a door engages into the frame is key, and the larger the door, the more difficult that becomes.
Ensuring flatness requires a keen knowledge of proper weld sequencing so that heat isn’t concentrated in one area, leading to warpage. Welders will check along the way to ensure straightness. Straightness and flatness of the outer frame are also critical, as that is where it will attach to the bulkhead — which must also be to spec — once delivered to the shipyard.
While the door and hatch specifications are designed by external engineers, the value of in-house engineering capabilities at a metal fabricator should not be underestimated. They’re the ones who will help develop weld mapping procedures, design jigs and fixtures, and ensure optimal rev control processes. They also ensure proper interpretation of drawings and can collaborate and perform DfM reviews prior to submission of the final drawings.
Preventing corrosion is a key factor in ensuring the structural integrity of watertight doors, hatches, and their working components. Consider whether the metal fabrication company has in-house priming and painting services that meet specifications for use on military vessels. In-house capabilities help to improve quality control, reduce lead times and unnecessary handling, and help drive down costs.
In addition to manufacturing the main structure of the door itself, the metal fabrication company must also ensure proper alignment and installation of all the door mechanisms. Doors may be sliding or hinged, each requiring special fittings. Depending on their size and function, some doors and hatches use hydraulic actuators while others may be operated manually.
All watertight units require proper seals, such as compression seals or inflatable gaskets. Some also use a dogging mechanism, a special type of latch that, in effect, wedges the door shut and seals it. These components must all mate precisely with each hole or access point on the door, sometimes requiring as minimal as .010-inch tolerance. Not all welders and fabricators can achieve that kind of precision.
If required by contract and specification, once completed, a metal fabrication company will conduct hydrostatic testing to ensure the sealing mechanism performs to specification. In one such test, a cavity containing the door and sealed frame is filled with pressurized water. The door and all its components must withstand leakage over a span of 24 hours.
A lot of engineering goes into designing the testing atmosphere and conditions, and not all fabrication facilities have the capabilities to perform such testing. It should be noted that Fox Valley Metal-Tech has rigorous in-house inspection, testing, and quality data package QDP documentation capabilities to meet stringent government requirements, and routinely works with government inspectors to ensure compliance.
Defense contractors that require a high level of precision on their custom watertight doors and hatches have come to trust Fox Valley Metal-Tech as a supplier of choice. Contact our team today to talk through your complex defense project and how our all-in-one services and expansive facility can deliver the results you demand.
To learn more about our dedication to precision and customer satisfaction, check out our defense industry case study below, featuring large metal enclosures for the Gerald R. Ford-Class Nuclear Aircraft Carrier.