Hi there, Stacey!
Welcome back to the Disney Parks Moms Panel! Your Disney Cruise Line vacation will be here before you know it and you will be so glad that you have everything planned beforehand. All you will have to do is show up and the fun will be waiting for you!
I have to be honest, at first glance, the excursions that you inquired about seemed very similar! I had to really look hard – and event contacted Disney Cruise Line – for some clarification so that I could be certain I was providing you with the correct information. From what I can tell, the
Nautilus Undersea Tour (G12) requires a short motorcoach ride to the dock where you will embark whereas you will walk to the dock to board the
Seaworld Observatory Semi-Submarine (G10). Additionally, the Nautilus Undersea Tour suggests that Guests bring plenty of sunscreen so that leads me to believe that the Nautilus vessel may not have as much of a covered area as the Semi-Submarine. There is a minor price difference between the two, but aside from that I cannot see anything significant between the two! I have not been on either excursion, so if none of the determining factors above are of importance to you, I would suggest considering what time(s) each are offered and see if a departure time sounds better for your traveling party! No matter which you choose, you will enjoy the experience you have and will have some excellent sights of sea life without having to don a swimsuit!
Wishing you a wonderful adventure at sea and at port!
Happy Sailing!
Stephanie