You cannot re-draw the same ship. If you own a ship it is removed from the "Ship Group" and all remaining options in the "Ship Group" are evenly weighted.
Ship Group A has 5 Ships in it.
If none of the ships are owned by the player,
each ship has 20% to be selected if "Ship Group A" is rolled.
If one of the ship is owned by a player,
each remaining ship (4) has 25% to be selected if "Ship Group A" is rolled
If all of the ships is owned by the player,
The Ship Group is disabled and other ship groups proportionally absorb the chance to be rolled
Example of Portional Distribution:
Ship Group A has a 10% chance to be rolled
Ship Group B has a 4% chance to be rolled
Ship Group C has a 1% chance to be rolled
If Ship Group A is disabled from a player owning all the ships, the 10% is distributed proportionally across the other two groups.
B will gain 4/5ths of the 10%.
C will gain 1/5th of the 10%
Ship Group B will have a 12% chance to be rolled (4% + (10% x .8) = 4% + 8% = 12%)
Ship Group C will have a 3% chance to be rolled (1% + (10% x .2) = 1% + 2% = 3%)
The % chance of rolling a Ship Group per container remains the same at 15% overall Ship Group chance.