Edit— actually I think that’s wrong. You should be able to get any app you have on your phone on your tablet as well, as long as you’re using the same Apple ID. However the phone version may not look as clear on your larger iPad screen.
I believe the only version available on the iPad is the HD version, you purchased the standard version for the iPhone. So yes, you’ll probably need to purchase it again.
The HD Version is the one that’s required for a tablet.
The reason for the HD version is the resolution tablets require. If you tried to run the phone version on a tablet, it’s resolution is not very good and would make it tough.
FWIW, I have run the standard def version on a Samsung tablet without issues. The HD version would certainly be better, but in my case it was not “required.”
On a related note, I just got a Iphone this weekend and am now wanting to get Navionics app. When I go to the app store there are many options which is the correct one for fishing?
What pool2fool said is correct. Once you buy the one you want you have a subscription for a year. This gets you unlimited updates which happen daily. After the year its $4.99 a per year after that.