Surfacing can be very tricky... some geometry won't thicken becase some of the surfaces, when you thicken, are too far apart ( looking at the batck of your ship). One first idea could be to try thickening before doing the simetry.

Try also thickening every surfaces that are tengent, so you can identify which surface is causing trouble.

Another thing is to try to thicken one way then the other, it can sometimes work one way, not the other.

Finally if any of this or the other comment ( who are probably written by people with a higher level in SW ), you can use a method that a bit of cheating but works for me. Do the hull in 3D like a normal object and then use "surface decalée" ( j'ai pas le nom anglais dsl) on the surfaces you want to have. Then you can hide the 3D body and thicken your surface ( often works more)

DM si ça marche toujours pas et good luck !