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First and foremost the vehicle must be able to tow an acoustic transducer at a depth of at least three meters. We use the 25kHz WHOI MicroModem as it is recognized as a competitive and up to date progress and our group has close ties with WHOI. The transducer is attached to a heavy towfish that weights down the towing cable and ensures the transducer hangs properly in the water. Speed is also important as the separation between vehicles can often be large and time on the water is limited. We've found that cruising around 2m/s provides a decent compromise between speed and endurance. We'd also wanted the vehicle to be capable of handling rougher sea conditions such as those found in open harbors.
Our target battery life was on the order of four hours, or a half day's operation. Ideally the batteries should be removable so they can be swapped out quickly when needed and be of a safe chemistry that can charge overnight. We also sought to keep the vehicle's two-man portable and small enough to fit in a rented SUV or uhaul. Operations can be a lot more flexible if neither a truck nor a hoist is required to transport and launch the vehicles.
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The hull of the vehicle is a Fuse 35 kayak from WaveSport. This is a kid's whitewater kayak, giving it a distinctly different size and shape from the more traditional kayak hull used by others such as the SCOUT. The bottom of the hull is almost completely flat and slopes upwards towards either end. It is wider as well, giving it a decent interior volume despite being just 1. 
8 meters long. The greater volume to length ratio and hopefully increased stability of a wider hull led us to choose a whitewater kayak over a traditional design.
