Ship shaking pls help

So i'm doing a ship warfare top view for ipad, and i have a ship 100x32 resolution. The problem is when i change the rectangle for my actual image, the ship, when it's not 90º or 0º it starts shaking while moving, that dint happen with the rectangle. I already tried to change for different resolutions, but always the same result 
I would appreciate any help thks,
Triped

I would appreciate any help thks,
Triped
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