I worked with Enerland for our boat's batteries. The batteries still cost $14,000. Since they have been bought by A123, You would need to start all over. Battery charging is also an issue. We used standard model boat chargers that could charge two batteries each. That took 21 chargers at around $100 each with a special discount for all the batteries in our boat. Custom chargers may be available but that would need to be investigated. Money is the biggest issue, and I'm not interested in financing anything like this.
We ran a quick change gear box with standard differential quick change gears to match motor rpm to the propeller. Gears are lots less expensive than propellers and it would take a custom design to run a propeller with a 4-5,000 rpm brushed motor. The prop we ran turned around 8,000 rpm. Brushless motors aren't as limited, but some way to match motors to propellers would be good. It also would be lower drag to run one propeller with the two motors. There may be synchronizing issues. We could avoid these problems with brushed motors and existing Zilla 2000 amp controllers like what we ran.
Manzanta makes the Zilla and has batteries and chargers as well. Brushed motors would be less efficient and might need more batteries. It would cost a lot less. Mike builds differentials for a living, so that's a possible source for a gear box. Below are some pictures of the boat and a graph of the data from the record runs. This proposed boat would be a much bigger project.
Lohring Miller