TM 5-1940-321-13&P
( 2 ) In addition to affecting speed and fuel consumption, loading also affects craft
handling. A lightly loaded craft will reach planning speed more quickly than
heavily loaded craft and is more responsive to turning. Craft loading also
affects ride quality in short, broken waves. A heavily loaded craft will have less
vertical motion under these lift as quickly to ride over a wave. Under certain
conditions, this can result in a heavily loaded craft taking on some water before
the craft lifts. This does not represent a danger, since inflatable boats have
extremely high ultimate buoyancy and will remain afloat when completely filled
with water. In addition to the amount of weight carried and placement of the
weight to achieve correct engine tilt, trim and balance are important.
b. Trim and Balance. Correct trim and balance are achieved by proper placement of weight
when loading the F530 IAB. This includes correct placement of crew, fuel, mission equipment, and cargo.
Proper trim and balance results in safe, predictable handling, good boat speed, and the best fuel
economy. There are two trim conditions: static and dynamic. Static trim refers to trim condition with the
craft at rest. Dynamic trim refers to the trim condition when the craft is underway.
( 1 ) Static Trim. When correctly loaded, the craft, when at rest and viewed from the
front or rear, should appear level. When at rest and viewed from the side, the
craft should appear almost level. A slightly raised bow is acceptable. A bow
down, stern up or a stern down, bow up condition is an indication that the fore
and aft static trim is not correct. Relocating weight to level the craft when it is
stationary accomplishes proper static trim. The affect of shifting weight to the
bow or stern will vary depending on speed, wave height, distance between
waves, boat speed, and boat loading.
( 2 ) Dynamic Trim. Trim may require change due to sea conditions. When waves are
arriving from the direction of the stern, shifting weight to the stern may improve
seaworthiness. When waves are arriving from the direction of the bow, shifting
weight to the bow may improve the seaworthiness. This is general guidance.
(a) Dynamic trim is also affected by the tilt angle adjustment of the outboard
engine. The outboard engine must be perpendicular to the water when the
craft is underway. Since the bow will be raised when underway, the outboard
engine trim angle adjustment can only be checked by operating the craft. The
outboard engine trim angle adjustment is most easily verified by observing,
from another craft or from shore, the angle the engine makes with the water
while underway.
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