# Wavy line appearing inside lofted-\>shelled boat hull
**URL:** https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584
**Category:** Modeling Questions
**Created:** [June 29, 2025, 6:51pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584 "2025-06-29T18:51:50Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@jgsparklab](https://discourse.shapr3d.com/u/jgsparklab)
#### Post date: [June 29, 2025, 6:51pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/1 "2025-06-29T18:51:50Z")
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 because the dimensions are small it would change the wavy line. It didn’t.
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### Author:  [@jgsparklab](https://discourse.shapr3d.com/u/jgsparklab)
#### Post date: [June 29, 2025, 6:55pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/2 "2025-06-29T18:55:49Z")
Here’s the file if anyone would like to inspect it.
[Training-boat-hull-loft-to-shell-inside-wavy-line.shapr](https://discourse.shapr3d.com/uploads/short-url/8gjQpYtWR3PAzv4RIJSNg5r3jAk.shapr) (138.3 KB)
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### Author:  [@Xdrakosha](https://discourse.shapr3d.com/u/Xdrakosha)
#### Post date: [June 29, 2025, 7:12pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/3 "2025-06-29T19:12:31Z")
Can’t tell you why is this happened but can tell you how to workaround the issue. Just make a negative shell.
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### Author:  [@SCALEMODEL](https://discourse.shapr3d.com/u/SCALEMODEL)
#### Post date: [June 29, 2025, 7:24pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/4 "2025-06-29T19:24:17Z")
If we had curve analysis tool we would probably see that curve crunches inward in an awkward way.
Also your 3 sketch the way you drew will not naturally connect to a point, so my recommendation would be continue your sketch to meet at a point.
If you have problem SHELL try split it in half and shell and mirror.
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### Author:  [@Xdrakosha](https://discourse.shapr3d.com/u/Xdrakosha)
#### Post date: [June 29, 2025, 7:52pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/5 "2025-06-29T19:52:09Z")
> [@jgsparklab](#):
>
> I scaled the design up thinking because the dimensions are small it would change the wavy line. It didn’t.
I can’t explain this issue from a mathematical point of view, but I feel it in my gut — the problem is that the bow of the boat is only 4 mm wide, and when we apply a 2 mm shell, there’s simply no room left to form a proper shape. If you scale it up, the shell works just fine.
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### Author:  [@jgsparklab](https://discourse.shapr3d.com/u/jgsparklab)
#### Post date: [June 29, 2025, 7:59pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/6 "2025-06-29T19:59:31Z")
Yes I see what you’re saying. Very interesting. I am just learning and was intrigued to see it buckle in the curve.
I’ll draw it again with some larger dimensions and see how it goes. I want to try multiple profile lofting so thought I’d start with a boat hull with a profile at the front end instead of a point.
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### Author:  [@SCALEMODEL](https://discourse.shapr3d.com/u/SCALEMODEL)
#### Post date: [June 29, 2025, 10:55pm UTC](https://discourse.shapr3d.com/t/wavy-line-appearing-inside-lofted-shelled-boat-hull/38584/7 "2025-06-29T22:55:42Z")
If you want more control because you want adjust the profile fitspline might be the better option for the profile curves.