I downloaded 'tidesplanner' when I fist got an iphone because it was free...
But if you want to look at a future date then you have to pay for it to be unlocked.
It's the only one I've tired but worth it for me as I stay near the beach in the summer and the iphone is the only method of getting on line.
If it's still free you can download it and have a play and if you pay to unlock the currents then you'll have them too.
I also use XCweather as they have a rose tint on their weather predictions
it's not an app as such but there is a way to make it a button on your phone, once you are looking at it turn your phone over to landscape to see the correct view.
Hope that helps dude