Here is my question....

I just completed a repower of my Dumas Donzi. Until this week, she was powered by 2 - 540 sized motors with a 2:1 gear reduction, powered by 2 - 7.2v batteries. It was a bit sluggish on the water so I installed 2 - Johnson HC970 motors with the same batteries (minus the gear reduction). The question I have is....would 2 - 7.2v batteries be considered a 14.4v system, or would it still only be running on 7.2v's? If I were to go to a 12v battery, would I see any increase in power?

Also, how could I increase run time? At full power, with this set up it only seems to run 10-15 minutes at most? What could I do to increase this? I've heard of large boats running for 4 hours at a time, is this possible?

Thanks.