System Overview
This analysis evaluates the feasibility of using a dinghy equipped with Yamaha Harmo 3.7kW RIM-drive electric motors as emergency propulsion for a 30,000 lb seastead with a 40×40 ft platform and angled columns.
Seastead Specifications
| Parameter | Value |
|---|---|
| Platform Size | 40 ft × 40 ft |
| Column Width | 4 ft |
| Column Depth | 13 ft at 45° angle |
| Estimated Weight | 30,000 lbs (13,600 kg) |
| Primary Propulsion | 2 submersible mixers with 2.5m propellers |
Yamaha Harmo 3.7kW Motor Analysis
The Yamaha Harmo 3.7kW is a rim-drive electric outboard with excellent static thrust efficiency:
| Specification | Value |
|---|---|
| Power | 3.7 kW (5 hp equivalent) |
| Static/Bollard Thrust | 227 lbs (103 kg) |
| Propeller | 15-inch ducted 4-blade |
| Weight | Approximately 50-60 lbs (based on similar units) |
| Special Features | Digital Electric Steering, powered raise/lower |
Efficiency Note: At 227 lbs thrust per 3.7kW (61.4 lbs/kW), the Harmo appears to be among the most efficient electric outboards for static thrust. For comparison, typical electric outboards range from 40-55 lbs/kW for static thrust.
Three-Motor Configuration
With three Harmo motors (one normally on dinghy plus two from storage):
- Total Thrust: Approximately 680 lbs (227 × 3)
- Total Power: 11.1 kW (15 hp equivalent)
- Control System: Yamaha's "Twin Mode" is designed for two motors, but three could potentially be controlled with custom wiring or using two controllers
Control System Options
Yamaha's Helm Master EX system includes:
- Joystick Control: Allows precise maneuvering with intuitive movements
- Remote Control: Wireless or wired handheld remote for basic operation
- Digital Electric Steering (DES): Electronic steering without mechanical linkages
Control cables are typically standard marine NMEA 2000 or proprietary Yamaha cables. They can be extended with appropriate marine-grade extension cables, though signal integrity over very long distances (>50 ft) might require boosters.
Performance Estimation
For a 30,000 lb seastead with high drag (similar to small oil platform):
- Drag Force at 0.5 mph: Approximately 150-250 lbs (depending on current and shape)
- Available Thrust: 680 lbs (theoretical maximum)
- Predicted Speed: 0.5-1.0 mph in calm conditions
- Power Requirements: Seastead could supply continuous power via umbilical cord
Conclusion: Yes, 3 Harmo motors should be able to move the seastead at approximately 0.5 mph in calm conditions, meeting your requirement.
Dinghy as Wave-Following Platform
Your observation about wave action is correct. Mounting motors on a dinghy provides important advantages:
- The dinghy naturally follows wave height changes
- Motors maintain consistent depth relative to water surface
- Avoids motors being submerged when mounted directly on seastead
- Provides directional flexibility for towing/pulling