TM 5-1940-321-13&P
d. Dual engine aluminum plate. Located inboard of the transom. This engine securing plate
can be used for single or dual engine operations. A molded hook located in the center of the plate is for
securing the outboard motor to the craft.
3-5. INFLATABLE KEEL (figure 3-14). The inflatable keel consists of the keel and single inflation valve with
valve cap stowage pouch. The inflatable keel is one of the major functional components. Its primary purpose is
to provide directional stability while underway. The fin-like action of the inflatable keel reduces yaw and allows
the operator to maintain a steady craft heading with less directional corrections of outboard engine steering.
The inflatable keel adds to the overall buoyancy and stability of the craft in several ways. It functions as a
backbone structural member and platform base for load distribution. It supports the flooring system for
increased rigidity and distributes loads imposed by personnel and cargo. It functions together with the port and
starboard lower buoyancy tubes to absorb some of the impact of pounding seas.
Figure 3-14. Inflatable Keel (Flooring Removed)
3-6. RIGID FLOORING SYSTEM. The rigid flooring system may be used in place of the roll-up flooring. The
rigid flooring system is recommended for use where transit distances exceed 5 miles, when using motors
having a rated horsepower higher than 40 hp, and when planning speeds with maximum payload are required.
The purpose of the rigid aluminum flooring system is to add more rigidity to the craft to achieve a lower drag,
which results in a higher planning speed with less power, greater ranger, and enhanced maneuverability and
fuel economy. The floorboards and stringers that make up the flooring system are made from a high-strength
aluminum alloy with an anodized finish.
3-7. LOWER BUOYANCY TUBES
a.
The lower buoyancy tubes are located beneath the main buoyancy tubes. They are inflated at
the same time as the upper buoyancy tube through connecting hoses from the aft compartments of the main
buoyancy tubes. Their function is to enhance planning characteristics of the craft and provide additional
buoyancy. The improved performance results from four basic functions.
( 1 ) The lower buoyancy tubes contribute to directing the under-hull airflow upward
giving the craft some lift and producing an air cushion at higher speeds.
( 2 ) This lift effect reduces time required to reach full planning speed, reduces the
angle of plane, and contributes to responsiveness in executing turns.
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