How to create a ship model?

[SCALEMODEL]

Wavy line appearing inside lofted->shelled boat hull

Hi. Trying to learn my way around loft function. I’ve created a bunch of sketches for a basic boat hull with two closed profiles and some guides. Lofting appears to go well. Then if I try and shell from the top surface the top sketch gets in the way. So I hide all the sketches in a folder. Finally I can shell the top surface. The shell happens but I get a odd wavy line inside the hull!? Can anyone shed some light on why the wavy line isn’t smooth as expected? I scaled the design up thinking be…