How to get grain heeling moments.


Question:

Can GHS calculate heeling moments due to grain shifting?


Answer:

If the grain holds are constructed such that pockets of voids cannot develop,
then you can heel the vessel in order to determine the heeling moment which
would occur if the surface of the grain were inclined to that angle. For
example,

  HEEL=20                                                                                             
  TC (HOLD*) ULLAGE: ... /VOLUME /NOSURF                                                              

shows the TCG of each hold in the heeled condition.  Multiplying the TCG shift
by the volume gives the volumetric heeling moment.

If it is a general cargo vessel where the hold is not specially constructed
for grain, you may want to take the voids into account in order to get lower
heeling moments.  For this purpose we have a program called GS (Grain Shift)
which handles the voids.  It produces a table of volumetric heeling moments as
a function of ullage.

Even with the aid of the GS program the task is formidable.  You have to build
your holds using several components in order to model the spaces between
girders where the voids can develop.  Information about the GS program is
attached.

After you have developed the volumetric heeling moments for each hold, you
have to multiply them by the grain densities and add them together to obtain
the total heeling moment which you would then use with the HMMT command.

In the case where the voids are not important, you can easily use GHS to model
grain shift. For example,

  HEEL=20
  LOAD (hold1) = x
  TYPE (hold1) FROZEN
  ...
  HEEL=0
  RA

This is still valid, though it may be too conservative, even when voids could
be present.