Mixers used in mobile aquaculture experiment
Vince Cate contacted Cliff Goudey, Director, Offshore Aquaculture Engineering Center, Massachusetts Institute of Technology, Sea Grant College Program. Cliff used some slow speed mixers to make a self propelled aquaculture cage which was tested near Puerto Rico. Some nice video of the propellers on the cage. These mixers can produce thrust of 3.4 kN/760 lbs from power input of 4.6 kW/6.2 hp. With two of these mounted in fixed positions he was able to control the 62 foot diameter cage like a normal twin screwed boat at 0.5 to 0.6 knots. He said a propeller/motor unit costs around $20,000. He used Toshiba Model VFS11-2037PME variable frequency motor controllers which cost about $1,600 each.
These 8 foot diameter propellers are off the shelf equipment used for very efficient mixing in the waste-water treatment industry.
- main Flygt mixer page.
- slow speed mixers - larger diameters and most efficeint
- compact mixers - smaller diameters and cheaper
These are noisy, not efficient at slow speeds, use a lot of gas, and probably not the best way to go for 24/7 thrusting. But for use just when near a port they could do fine.
For up to about 300 lbs of thrust you can get electric trolling motors.
Big ships have electric or hydraulic thrusters to ease up to a pier. For example, bow thrusters. These might be reasonable for a seastead thruster.
Some ships use large azimuth thrusters. Not clear these come in small enough sizes for seastead use.
Starter motor on outboard motor
The electric starter motor on a gasoline outboard motor has enough power to turn the prop with significant push (Vince has done this when there was no gas getting to the engine). So it might be reasonable to convert an old engine to electric only use.