It's DC for plug and play convenience, forget about relays.
Terramex, it seems that if you turn on that motor, some spiders are going to loose their home.
I've made some tests, and the water drag is incredible. Just realized that was a mistake when I said that the bare hub makes 9700 rpm underwater. The motor with the base disk makes about 10500 rpm on air, and between 2200 and 3000 in water, depending on the amount of air bubbles inside the hub.
Just discovered that a small amout of air, between the coils and the magnet, improves performance a lot. Those are two concentric cylindrical surfaces very close together, and the viscosity of water between them makes a big drag.