Ship shaking pls help

Triped

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

Clouds

Too much information.