Boat hull

Hello my mesh boat hull is diving inwards when ever put a floor in the hull dives inwards when ever I put it into catmull-clark

I would say there are either internal faces or non manifold areas in there but without the blend, that’s all i can guess

Don’t connect the floor to the hull. In fact, you might even want to make them separate objects.

If using subdivision surface you need to add edge loops to support the edges that you want to remain sharp. If you post a blend or even wire screen grabs better advice may be had.

A wire frame screen grab would probably confirm what we can infer from the posted image: one object, subsurfed to level 4, mirror modifier… OP complains that when he ‘puts in a floor’ and turns on subsurf the problem shows up. Unless Coldpaws has discovered a completely new way of screwing up a mesh, it’s pretty sure to be interior faces or maybe a non-manifold mesh.

@Coldpaws, don’t mind us, just shoptalk. Welcome to BlenderArtists :smiley:

(PS, not much point in setting your subdivision view level higher than your subdivision render level, unless you just did that to make the problem clear. Do a screenshot in Edit Mode, vertex or edge select mode, to get the ‘wires’ screenshot people are talking about.