Question:

How do I model the hook load suspended from a crane?

Answer:

Here is the the proper way to represent the hook load on your crane:

ADD "Hook load" wt, l, t, v /len: b1, b2

where,

wt - the hook load weight,

l, t, v - the coordinates of the sheave,

b1, b2 - the longitudinal coordinates of the crane base.

In most cases it is more realistic to adjust b1 and b2 according to the azimuth angle of the crane rather than to keep them constant:

b1 = b0 - x
b2 = b0 + x
x = r*cos(a)

where,

b0 - the longitudinal center of the crane base,
r - the radius of the track
a - the azimuth angle (0 is off the stern)

For convenience, the add command can be replaced with the BOOM command which computes l, t and v given the crane angles and the effective boom length.

All of the elements of the crane -- boom, counterweight and any other rotating weights -- should be represented in a similar fashion.