Large diameter, low RPM propellers for efficient low-speed thrust
Your requirement: Efficient propulsion for a 30,000 lb seastead moving at 0.5-1 MPH using large diameter (2500mm+) propellers at 1-5 kW power.
Solution: Submersible wastewater mixers ("banana propellers") appear to be a viable, cost-effective option compared to marine thrusters.
Key findings: Several Chinese manufacturers offer 2500mm mixers with 400-900 lbs thrust at 3-5.5 kW for $2,000-$5,000. European/Japanese options offer higher quality but at 3-5x the price.
To move a 30,000 lb (13,600 kg) seastead at 0.5-1 MPH:
Note: Differential thrust steering with two widely spaced thrusters is an excellent approach for your application.
| Manufacturer | Model | Propeller Size | Power | Thrust | Construction | Estimated Price | Notes |
|---|---|---|---|---|---|---|---|
| Shinmaywa (Japan) | SM-VRTN | 2500 mm | 2–3.2 kW | 720 lbs (3200 N) | Stainless steel | $8,000 - $12,000 | High quality, seawater compatible, includes VFD |
| VIVAMIX (China) | VML2500/3kW | 2500 mm | 3 kW | 470 lbs (2090 N) | Cast iron / SS option | $2,000 - $4,000 | Best value, 220V 3-phase, saltwater option needed |
| Qiankun (China) | QJB4/4-2500/2-42P | 2500 mm | 4 kW | 463 lbs (210 kg force) | Cast iron | $2,500 - $4,500 | Common design, multiple suppliers |
| Chinese Supplier | QDT5.5/4-2500/2-47 | 2500 mm | 5.5 kW | 863 lbs (3840 N) | Cast iron | $3,500 - $6,000 | Highest thrust option reviewed |
| PTM Mixer (Europe) | Phantom 2500 | 2500 mm | 2.5-5.5 kW | Not specified | Stainless steel | $12,000 - $15,000 | High quality, likely includes VFD |
| Flygt/Xylem | 4410 Series | Various | 1.5-4 kW | Best thrust/kW | Stainless steel | $10,000 - $20,000 | Premium option, most efficient |
Saltwater Compatibility: Most submersible mixers are designed for wastewater treatment, not seawater. Stainless steel (316L or better) is essential for saltwater use. Cast iron will corrode quickly.
Variable Speed Control: These mixers typically require separate Variable Frequency Drives (VFDs) for speed control, adding $500-$2,000 per unit.
Purpose: Control motor speed by adjusting frequency and voltage
Cost Range: $500-$2,000 per unit for 3-5.5 kW drives
Required Features: Saltwater environment rating, marine-grade enclosure, compatible with 3-phase motors
Separate Purchase: Mixers typically sold without controllers
Integration: Need custom mounting and steering control system
Power Supply: Your solar system needs to provide stable 3-phase AC or you'll need DC-AC inverters
Option 1 (Budget): Two VIVAMIX VML2500/3kW units in stainless steel configuration with VFDs
Option 2 (Higher Thrust): Two QDT5.5/4-2500/2-47 units
These are specifically designed for seawater and may be more suitable:
For comparison, purpose-built marine thrusters:
VIVAMIX: Luna (+86 13522525054) - luna@ecowatertechs.com
General Sourcing: Alibaba.com has numerous suppliers - request stainless steel construction and seawater compatibility
Verification: Always get actual quotes with detailed specifications for saltwater use
Design rotating mounts for directional thrust
Ensure proper depth (fully submerged) for efficient operation
Consider retractable mechanism for maintenance
VFDs should be located in dry, accessible areas
Plan for 3-phase power conversion from your DC solar system
Include emergency shutoffs and manual overrides
Differential thrust control for steering
Speed control via joystick or automated heading control
Feedback system for position holding if desired
Next Steps: Contact 2-3 Chinese manufacturers for detailed quotes on stainless steel versions with seawater compatibility. Request performance curves showing thrust vs power at various speeds. Order one unit for testing before committing to full system.