P&N uses gravitic cloaking levels up to about level 1400, in order to make the relative effectiveness of sensors easier to grasp. 1500- tonnage of ship = gravitic cloak level of ship.
I just created a level 6 cloaked ship hull for my Tug of War game and it works perfectly.
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All that is gold does not glitter,
Not all those who wander are lost;
The old that is strong does not wither,
Deep roots are not reached by the frost.