Question for Source SDK mappers!

OK, I have been searching the Internets for hours now but nothing. I know this isn’t exactly a mappers forum but FPS Banana is down (like always) and I don’t really know anywhere else I should ask. I need to make a func_physbox that can float. Easy right? Just set the physical property to wood. I did, but the brush is so large (Its going to be my ships hull) that it just sinks. Weirdly there is no setting for buoyancy or for weight (there is a setting for mass but that’s falling speed not weight). Any ideas on how I can make my brush float?