This is due to how the engine orders the drawing of transparent parts. It is based on the distance of the center of the object to the plane on which the camera lies. See these for an explanation:
So when you turn the camera around your ship, the center of the sail is sometimes closer to the camera plane, but the center of the rope net is closer from some camera angles. This is why the ordering flickers even though it shouldn’t if this was rendered with a 100% correct ordering.
This is a known issue, there’s not really a good method in computer graphics that renders transparent part in a 100% correct order that is also computationally efficient and portable across different kinds of hardware.
Here is some more discussion in this thread:
https://devforum.roblox.com/t/decal-fog-rendering-bug/20034
You can also search for “user:zeuxcg transparency” or “user:zeuxcg transparent” to get more discussion about transparency issues posted by zeuxcg.