Will navy blue tattoo ink cover black tattoo ink?

Not completely. You may still see the black ink through the navy blue, coloured inks are opaque meaning there is colour but you can still see darker colours throuhg them. The only thing that will cover black ink is black ink. But some times you can get away with hiding it in a cover up. Have a few consultations with a tattooist in your area and see if they can design a cover up tattoo for you.