1. Do RIM Drives have a "Spin Freely" mode?
Yes, but there are important hydrodynamic factors to consider regarding drag.
- Mechanical Freewheeling: Because Rim-Driven Thrusters (RDTs) are hubless and do not connect to a central gearbox or driveshaft, they have very low mechanical friction. They typically rely on water-lubricated hydrodynamic bearings. When power is cut, water flowing through the duct will cause the blades to spin relatively freely.
- Induced vs. Duct Drag: Even when freewheeling, the thruster will create drag. The duct (Kort nozzle) itself generates form drag, and the blades, acting like a turbine, generate induced drag. It will be less drag than a locked propeller, but more drag than a smooth hull.
- Advanced "Zero-Torque" Mode: Many modern electric motor controllers can be programmed to use a tiny amount of electricity to match the RPM of the propeller to the speed of the water flowing through it. This eliminates the turbine-drag effect, bringing the drag coefficient down to essentially just the friction of the duct itself.
- Hydrogeneration (Bonus): Since the RIM drives turn when dragged through the water by your kite propulsion, you could use them as hydroelectric generators. This will increase drag, but it allows the kite to charge your battery banks!
2. What do I think of the Kite Robot idea?
The concept is brilliant and highly synergistic with your hull design. Because your three legs have NACA foil shapes with a 10-foot chord and 3-foot width, they act exactly like massive daggerboards. This gives the seastead tremendous lateral resistance, allowing a kite to easily pull you upwind without sideslipping. The windsurfer analogy—moving the center of effort forward to fall off the wind, and backward to head up into the wind—is mechanically sound.
The Standout Pros
- Independent Redundancy: As a completely separate propulsion layout, it provides incredible safety if the electrical drive fails.
- Dynamic Steering: Moving the robot along the track uses the geometry of the trimaran to steer, potentially eliminating the need to use thrusters for rudder control while sailing.
- Clean Living Area: Keeping the track on the outer port, bow, and starboard rails ensures the chaotic and dangerous high-tension kite lines are nowhere near the living quarters or the dinghy aft.
- High Altitude Winds: A kite accesses much stronger, cleaner winds than a traditional mast and sail, avoiding the wind shadow of the 7-foot living quarters.
Design Challenges to Solve
- Track Captivation (Derailment Risk): A kite stack generates tremendous lifting force. The robot cannot just sit "on" an I-beam; its wheels must be fully captivated (like a roller coaster) to resist moving upward and outward off the rail.
- Heeling Moment: A 40ft wide triangle provides excellent initial stability, but flying powerful kites off the side will impart a massive rolling force. Your active stabilizers (the airplane tails) will have to work constantly and aggressively to counter this.
- Kite Relaunch: Stacking 20-50 kites is great for scaling power up and down. However, if the stack crashes into the ocean, water-relaunching a 50-stack is nearly impossible.
Specific Recommendations for the Kite System
- Powering the Robot: Instead of dragging a physical extension cord along the railing (which can snag) or using heavy batteries, consider an enclosed electrified busbar track—similar to a subway's third rail or an amusement park bumper car. The robot can draw power continuously for its winches and line-adjustments while it rolls.
- Regenerative Kiting: You mentioned the kite pulling the robot back and forth to charge batteries. This is known as "Airborne Wind Energy" (yo-yo generation). While feasible, placing that complex mechanical load on a curved track is highly prone to jamming. Recommendation: Use the kite to pull the seastead forward, and use your RIM drives in reverse to regenerate electricity. It's much simpler mechanically.
- Launch/Retrieval Zone: Having the human stand near the bow while the robot flies the kite at the zenith (directly overhead) is a great idea. At the zenith, the kite generates minimal forward/side pull, only vertical lift, making it much safer for the human operator to clip/unclip the kites from the stack tether.
3. Synthesis with Active Stabilizers
Your trailing "small airplane" stabilizers are the key to making this kite system work. Because a seastead with a small waterplane area (SWATH-like) is sensitive to weight shifts and wind heeling, the kites will try to pitch the bows down and roll the seastead to leeward.
By using the kite pull to generate forward boat speed, water will flow rapidly over your stabilizers. The small actuators adjusting the angle of attack on these horizontal foils will generate immediate dynamic righting moments—pushing down on the leeward foil and lifting the bow foil—keeping your living room perfectly level while sailing under kite power.