Reply To: Fins deform after joining.

[spikeyxxx]

Hi stawpeed, thanks for the .blend file.

You have double vertices in you fins:

Remove doubles solves that:

Easiest solution is to select all the five fins in Object Mode, then go into Edit Mode, select everything with A and then press M > Merge by Distance when using 2.83+ or press ALT+M > Merge by Distance if you are using 2.82 or before.

Then you can join them.