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detailed picture of thrsuter mounting, perhaps more description of the shaft seal
Power
The power electronics for the kayak are designed around a constant load of 50 amps. In practice this is higher than what is observed even at max thrust and much higher than the current consumption when traveling at 2m/s. The original kayak design used a number of Lithium Polymer batteries connected in parallel inside the main CPU box. This arrangement provided good energy to weight ratio and simplified wiring, but batteries could not be swapped. LiPo batteries are also notorious for their tendency toward fiery accidents and charging had to be carefully supervised.
Lithium Iron Phosphate (LiFePO4) batteries are now used instead. While not as high as LiPo's, this chemistry still provides an energy density about twice that of a conventional lead acid battery. They are also much more stable and there is almost no risk of explosion or fire, even when overcharged. We use 12.8V 100Ah battery packs purchased from www.batteryspace.com. Tests with a DC load have shown the 100Ah capacity rating to be accurate to within a few amp-hours. We house these batteries inside plastic ammo cans to make them splash proof. Two waterproof connectors provide power and balance connection to the battery.
While these batteries can be charged safely without balancing, the use of a balancer helps improve longevity. Fitting every battery with a built in balancer board would be expensive and difficult to accomplish given the minimal space available in our battery packaging solution. Instead we charge the batteries using FMA Powerlab 6 chargers from ProgressiveRC. These chargers can give a high 40 amp charge rate and a decent 1 amp balance current. Unlike many other chargers, the FMA Powerlab can also be configured to charge a 100Ah battery without running into any safety timer or capacity limit issues. We mount two of these chargers and a 27volt, 40 amp power supply in a pelican case as a mobile charging station.