Design, Manufacturing, and Testing of an Improved Watertight Door ...

Design, Manufacturing, and Testing of an Improved Watertight Door
94 &2010 #4
These requirements will be further elucidated in
subsequent sections. From the outset, it was
clear that the design should focus on a single
watertight door configuration meeting specified
size and pressure requirements. Of particular interest
were the possibilities of applying the
accuracy and high speed of automated laser cutting
and welding in manufacturing the panel and
frame, and also developing a hydraulically
(water pressure) actuated seal system.
Watertight Door Selection
Initially, the intent was to develop a design and
manufacturing methodology that would apply
to all sizes and configurations of watertight closures;
however, it soon became obvious that this
scope was too broad to be accomplished with the
available resources. It was decided to select a
single watertight door configuration and, after
the design and manufacturing methodology had
been established on this door, to extend the
principles to other door sizes and configurations.
After consultation with the NAVSEA technical
warrant holder for ship hull outfitting systems,
engineering colleagues at the Naval Surface
Warfare Center Carderock Division, Ship Systems
Engineering Station, Philadelphia
(NSWCCD), and Northrop Grumman Corporation
Newport News (NGCNN), it was decided
to attempt to design a replacement for the 26 in.
66 in., quick acting, 10 psi NSWTD with a
6 in. light (window). The 26 66 NSWTD configuration
is the most widely used configuration
in aircraft carriers and ships across the fleet. A
quick acting door is one in which the dogs are
simultaneously operated by a single handle
through a series of linkages. The door configuration
selected for replacement has eight dogs
(latches) and two hinges. The weight of the
10 psi NSWTD is 290 lbs (including door panel,
frame, and associated hardware). Interior and
exterior view assembly drawings of this watertight
door are shown in Figure 1.
& The NSWTD’s marginal performance is related
to several design features: the NSWTD is
made mostly of low carbon steel. It must be
painted or powder coated and the painted
surface must be constantly maintained to
avoid rust.
& The NSWTD is sealed by forcing a knife edge
against a silicone rubber gasket as illustrated
in Figure 2. The NSWTD must maintain its
seal for water loading both on the interior and
exterior sides. While loading on the exterior
side of the panel forces the gasket against the
knife edge, loading on the interior side forces
it away from the gasket. This must be resisted
by force applied by the dogs to the wedges in
order to maintain contact between the knife
edge and the gasket. These forces are large,
and sources of mechanical wear. Also, to
properly seat the knife edge on the gasket and
avoid pinching it on the hinge side, a ‘‘yoking’’
hinge is required.
& The lap-welded bulkhead installation concept
for the NSWTD frame assembly can introduce
distortion into the NSWTD door frame, resulting
in high mechanical operating forces
that frequently result in cascading secondary
component failures.
As shown in Figure 3, the frame is attached to the
bulkhead by two lap welds requiring contact between
the frame and the bulkhead; however,
bulkheads are typically not flat. As a consequence,
the knife edge may become wavy due to
conformance with the existing bulkhead surface.
Adjustment of the hinges and dogging mechanism
during installation and frequent inspection
and adjustment in-service are required to ensure
that the knife edge maintains proper contact
with the gasket.
Initial Design Strategies forNewDoor
On a stiffness per pound basis, reinforcing the
panel sheet by welding angle irons on one side,
cupping the rims, and indenting the sheet is not
very efficient. Square or rectangular honeycomb
panels, with the spacing and thickness of the face
sheets properly sized, are more efficient in bending
or uniform pressure loading because in crosssection
they place the bulk of material at a
greater distance from the neutral axis increasing
the second moment of inertia. Honeycomb panel
structures bonded by adhesives are often used in
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