Inclining pendulum

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Inclining Pendulum

An inclining pendulum setup is used in an inclining test to measure a vessels VCG location.

Construction

The pendulum is rigidly fixed to a vessel, preferrably along the centreline. The attachment point may be a pre-existing beam, or may be a rod or piece of timber clamped to the ships structure. A nail typically serves as the pivot, with ring or washer used to minimize the contact patch at the pivot. A long line is run vertically. This line may be weighted if the pendulum is hung on the vessels exterior, to help minimize the effects of wind. As a longer line produces more accurate angle readings, pendulums are often hung from masts, ladders, superstructures or through access hatches to provide sufficient length. The bottom of the pendulum is weighted, either with a collected mass (such as a number of nuts) or preferrably with a mass with large planar faces. This mass is best suspended in a liquid, such as water or oil. The liquid dampens movements, allowing for easier readings. Behind the bucket, a scale attached to rigid cross member is used to measure the horizontal offset of the pendulum.

Measurements

The pendulum measures the heel angle resulting from an induced heeling moment, produced by a number of inclining masses. As the length of the pendulum can be measured, and the horizontal distance can be measured, the angle of heel can be accurately calculated as the ARCTAN (Horizontal Distance / Vertical Distance).

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