By
DON NELSON, EDITOR
Passengers out for a test ride on the Navy's new 36' rigid
inflatable boat in early May were surprised by a non-event.
As we headed into a 3' chop on New Orleans' Lake Pontchartrain
and began accelerating to 45 knots, we braced for a sole-pounding
experience. It never occurred.
"The hull can
take a 30-G force on the bottom and you'll only feel 4 Gs
at your feet," said Chris Bukosky, project manager
at the yard that built the Naval Special Warfare RIB, United
States Marine Inc.
USMI President Larry Ellis said two features of the hull
smooth out the bumps. "For one thing, we've got a higher
degree of deadrise (24.4' at the transom) than a lot of
commercial and military craft," he explained. "We
find that going that high gives you a softer entry. The
other thing is the cored construction. We use Airex for
the core, a nonlinear PVC foam. When you do take an impact,
it's absorbed by the outer skin and by the Airex core, which
transmits the impact throughout the structure."
USMI surrounded
the core with a custom-mixed, high-elongation resin and
Kevlar aramid fibers. The topside has a Divinycell core,
which flexes less than Airex.
Overall, the craft
measures 36'4"xl0'6"x2'7" and draws 3'. It
carries a fully equipped team of eight Navy SEALS, a three-man
crew and has a payload capacity of 3,200 lbs.
U.S. Marine based
the RIB, the 11th in a series of 70 it's building for the
Navy, on a design it developed in 1988.
The only significant
change to the hull involved blunting the bow, to accommodate
the vessel's collar. Demaree Inflatable Boats Inc. is sup-
plying the collars for the contract.
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NIMBLE
AND FAST
The new RIB's relatively soft ride disguises its true personality.
Its Mission, after all, is to transport SEALs to and from
combat environments. That requires a highly maneuverable
craft with loads of power.
Twin KaMeWa FF 280
waterjets give the driver hair-trigger control over the
vessel's direction. It turns on a dime at speed, a fact
that leads smart passengers to keep a tight grip on the
handholds at all times. (One Navy officer who didn't found
himself sitting in the water shortly after his driver began
demonstrating the boat's diminutive turning radius.)
The jets also can
be back-flushed. Bukosky said that of the eight boat- builders
that bid on the contract, only U.S. Marine's design had
this capability. "I think it's a big reason the Navy
picked us," he said. "These boats will
be in littoral warfare,
where there's a lot of debris in the water, and you have
to be able to flush it out."
As for speed, Bukosky
said "it's the fastest production boat in the Navy."
The Navy has prohibited the builder from divulging anything
about the top speed other than that the boat travels at
"45-plus knots."
Two specially designed
Caterpillar 3126 turbo charged engines push the craft. Each
develops 470 hp at 2,950 rpm. That model of engine normally
puts out 420 hp.
The engine supplier,
Puckett Machinery Co., teamed up with Caterpillar's Defense
and Federal Projects Group and USMI to squeeze out the extra
power from the mains.
"We have a
dynamometer in Jackson (Miss.), and we did a lot of experimentation
with timing and fuel systems," said
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