Can GHS calculate the ground reactions when ground points are defined and
initial ground reactions are not?

Yes.  You do not need to know what the initial ground reactions are.  You can
use zero, or a guess.  If the given initial reactions are less than required
to support the vessel, it will "settle down" until the required reactions
develop.  This will increase the draft somewhat, but since the ground is
usually quite stiff relative to the water, the increase in draft may not be
significant.  If you want to refine the solution, observe the final reactions
and then plug them in as the initial reactions and solve again.

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