General HydroStatics
Ship Stability Software
Command of the Week
(New or interesting aspects of GHS that you may not know about)

/LEN: x1, x2
(Requires GHS with Longitudinal Strength module)

/LEN and its variation /PLEN are parameters we use to distribute a given weight over a length for longitudinal strength calculations. The ADD and BOOM commands offer these parameters.

/LEN is a convenient alternative to providing a density curve if the weight distribution is linear over a longitudinal distance. The center of gravity of the weight need not lie midway between x1 and x2.

Particularly interesting are the cases where the weight is not attached directly to the hull girder but is cantilevered out at some distance from its base. In these cases the weight distribution may include a negative area, making the /LEN parameter especially convenient.

A prime example is a crane, where its weights are supported within the span of its base.

Shown below is a Longitudinal Strength plot. The red line is the weight density curve, the blue or cyan line is the sheer curve, and the green line is bending moment.

The influence of the crane on the weight distribution is quite visible because of the positive and negative weight density extremes needed to resolve the weight into a relatively short base. The cantilevered heliport is supported over a longer distance and the arm to the C.G. is shorter, so the weight-curve variation is not so extreme though the magnitudes of the weights are the same.

Largest Shear: 404.8 MT at 10.100f

The /PLEN version yields the weight density as a constant value with pos/neg point weights at x1 and x2. Though the weight curve looks much different, it integrates out to similar shear and bending-moment influences. One version might be more suitable than the other for cranes, depending on the design of the base.

(There is a scale change between this plot and the previous one.)

Largest Shear: 306.9 MT at 11.500f

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