I will have simple gravity cores that penetrate the benthic layer (bay floor) of the estuary. The core will contain mostly sediment, but ~20% of the core will contain the overlying water. While I'm waiting for the probes in the sediment to equilibriate, I want the overlying water to stay well-mixed. With that, I'll need some sort of stirring mechanism that is on the underside of the core cap, in the overlying water, but not on the sediment.
My thought was to adhere a small RC boat or submarine motor and propeller to stir the water with a small hole in the core cap would be cut to run the electrical. Unfortunately, the closest thing I came across was a completely sealed unit that only runs for an hour on its battery. I would need it to run for about 24 hours.