Most yachts have a multitude of thru-hull fittings located below
the waterline. These numerous inlets, which supply seawater, are typically
required for refrigeration pumps, engine / generator cooling, sanitary
flush use, watermaker supply, wash-down pumps etc.
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| USCG and ABYC regulations require that a "seacock" (a robust flanged
valve) be installed at every
thru-hull fitting located below the waterline. Despite this expensive
complexity, the catastrophic failure of any thru-hull
fitting poses a significant threat to vessel safety. In the event
of a thru-hull fitting's failure, the resulting hull breach could result
in a substantial leak. |
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Real ships use a common flooded cavity, known as a "sea chest",
to supply seawater for the plethora of demands aboard.
The sea chest's thru-hull inlet(s) are contained within integral interior
walls which extend well above the vessel's waterline. This compartment
is always flooded, yet seawater
cannot rise above the seachest walls under any circumstances. A watertight
hatch, located at the compartment's top for interior access, prevents
overflow of seawater.
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SEDATION 4 has an integral
seachest behind the robust Aft-Main bulkhead of each hull. This location
is least vulnerable to damage from impact and positions the water pick-ups
in deeper water when beached. The inlets are located toward the center
of the vessel, on the opposite sides of the keels from the heads' overboard
discharge thru-hulls. This "staggered
thru-hull" configuration minimizes cross-contamination between
overboard discharge and seawater intake. The only other underwater hole accommodates
the Furuno depth sounder's transducer.
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One Ø2" thru-hull hole was drilled in each hull, perpendicular to
the hull's outer surface. A close examination of this photo reveals
the extensive laminate composition. |
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Backing blocks, for the Forespar Maralon seacocks, were fabricated
from 1" thick Nida-Core. Here, the backing plate
has been aligned with the hole's centerline inside the port hull.
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| Each was laminated in place using a spare thru-hull fitting for
clamping pressure and to assure concentricity with the hole in the hull.
This measure also assures that the backing blocks' upper surfaces are perpendicular
to the thru-hulls' centerlines for optimum loading of the seacocks' flanges.
This one is now properly
bedded in-place. |
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