Gravwood is such a wonderous material. It cancels 1G of force for itself and 50% of its "standard weight" making it perfect for airships and subsequently for spelljamming ships. I had a figter once in this campaign who decided he was going to make a spear out of gravwood, thus eliminating the maximum range of the weapon. Worked well for months and he even spent the majority of his hard earned cash (stolen from the dead) to have the item enchanted. I still fondly remember the look on his face when he one day criticaly fumbled a throw, sending his beloved, and quite expensive, spear out into the stars....never to be seen again. Many character years later I gave him an extra 100xp for accidentaly killing a space dolphin with the spear, but he seemed not to be pleased with this most unbelievable feat.