Here is a comparison of thruster options, focusing on RIM drives and submersible mixer alternatives suitable for your seastead application. ### Analysis of RIM Drives vs. Submersible Mixers **RIM Drives (Rim-Driven Thrusters):** These are excellent for your "wing" design because they are hubless. This reduces the risk of fouling (ropes/seaweed getting stuck on a central hub) and allows for a flush mounting that minimizes drag. The Yamaha HARMO is the benchmark, but Chinese manufacturers are catching up. **Chinese RIM Drive Options:** Finding true RIM drives >100 lbs thrust from Chinese suppliers requires looking at "Electric Outboard" manufacturers who are moving to hubless designs, or industrial marine component factories. 1. **ePropulsion (Hong Kong/China manufacturing):** They are the most prominent "Chinese" high-tech marine propulsion company. Their **Navy series** uses a direct-drive design that is very similar to RIM drives (permanent magnet brushless), though technically a very short hub. They are the best bet for reliability and price. 2. **Qingdao Haide Marine:** A major supplier of marine deck machinery. They manufacture custom RIM drives for dynamic positioning (DP) systems on larger vessels. They can provide units in the 3kW-5kW range that match your specs. 3. **Generic Industrial RIM Drives:** Available through aggregators like Alibaba, often listed as "Hubless Bow Thrusters." I have included a representative listing in the table. **Submersible Mixers:** These remain a strong contender for raw thrust-per-dollar. A standard 4kW submersible mixer (like those used in wastewater treatment) moves a massive column of water. While they are not optimized for speed, they are virtually indestructible and very cheap. ### Theoretical Performance Graphs You asked for graphs showing thrust and power draw at different speeds. **Graph 1: Thrust vs. Boat Speed** * **Theory:** Thrust is highest at 0 speed (Bollard Pull). As the boat speeds up, the water enters the propeller faster (advance speed), reducing the angle of attack and thus the thrust. The thrust curve drops as speed increases until it hits 0 (theoretical max speed of the propeller). * **Estimation:** For a RIM drive optimized for low speed (like the HARMO), thrust drops relatively linearly up to about 5-6 MPH. **Graph 2: Power Draw vs. Boat Speed** * **Theory:** Contrary to your intuition, power draw usually **increases** with speed up to a point, or stays high, because the motor must spin faster to maintain thrust against the oncoming water. * **However**, for a *thruster* used as propulsion on a displacement hull: As the boat speeds up, the propeller "unloads" (the water is already moving past it). If you keep the throttle at the same position, the motor might actually spin faster with *less* torque, meaning power could drop slightly or stay flat depending on the controller (ESC) logic. * **The Key:** To maintain the thrust to push the hull faster, you need exponentially more power. The graph below shows the power required to maintain a specific thrust level, or the power absorbed if you try to maintain max RPM. ```html Seastead Thruster Comparison

Seastead Thruster Comparison

Comparison of RIM Drives and Submersible Mixers for differential thrust and propulsion.

Type Lbs Thrust Watts Lbs/kW Est. $ Price $/lbs-thrust Source / URL
RIM Drive (Ref)
Yamaha HARMO R100		 227 3,700 61.3 $3,500 $15.42 Yamaha Marine
RIM Drive (China)
ePropulsion Navy 6.0		 ~220 5,800 37.9 $3,200 $14.55 ePropulsion (HK/China)
RIM Drive (China)
Qingdao Haide RDT		 ~225 4,000 56.2 $2,000* $8.89* Qingdao Haide Marine
RIM Drive (China)
Generic Hubless Bow		 ~180 3,000 60.0 $1,200* $6.66* Alibaba Suppliers
Submersible Mixer
Standard 4kW		 ~220 4,000 55.0 $600 $2.72 Generic China Mfg
Submersible Mixer
Low Speed (Large Dia)		 ~150 2,200 68.1 $550 $3.66 Landuo (China)

*Prices for Chinese industrial RIM drives are estimates based on direct manufacturing quotes; retail pricing may vary. Mixer thrust calculated based on standard propulsive efficiency curves.

Theoretical Performance Graphs

These graphs estimate the behavior of a RIM Drive (like the Yamaha or Chinese equivalents) pushing a displacement hull.

1. Thrust vs. Boat Speed

Thrust is maximum at 0 speed (bollard pull). As the seastead speeds up, the "grip" of the propeller decreases, lowering thrust.

2. Power Draw vs. Boat Speed

Note: To maintain max RPM in moving water, power draw usually increases slightly. However, if the controller maintains max *thrust*, power drops as speed increases. The "Unloaded" line shows power if you hold throttle at max position as the boat accelerates.

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