This document outlines a diver-less, reusable, electric-drive helical mooring system for both the ½-scale prototype and the full-scale seastead. The design uses a stainless-steel helical anchor, a reusable torque-transfer shaft, and an above-water electric motor/gearbox assembly. The system is optimized for frequent relocation (weekly or even daily) and tension-leg parking.
Target: 1,000 lbs working tension per screw | Water depth: 8 ft | Anchor: 6"Ø single helix, 8 ft shaft, ~7 ft embedment in sand.
| Component | Specs / Notes | Qty | Est. Unit Cost | Est. Total |
|---|---|---|---|---|
| Helical Anchor | SS316, 6"Ø helix (¼" plate), 2" pipe shaft, 8' long, welded mooring eye | 3 | $450 | $1,350 |
| Reusable Drive Shaft | SS316, 2" pipe, 10' long, J-slot quick-coupler at bottom, motor flange at top | 1 | $550 | $550 |
| Electric Drive Unit | 4 kW 3-phase motor + 50:1 cycloidal gearbox + VFD (380V or 220V), marine-duty enclosure | 1 | $750 | $750 |
| Portable Gantry Frame | Galvanized steel A-frame, torque reaction arm, guide sheave, clamps to deck edge | 1 | $350 | $350 |
| Mooring Pendants | 3/8" UHMWPE (Dyneema), 15' length, spliced thimbles, SS316 shackle & swivel | 3 | $90 | $270 |
| Alignment Funnel | SS304 guide collar to keep drive shaft centered over anchor during engagement | 1 | $150 | $150 |
| Shipping / Import / Misc | Freight from China, customs, hardware, spare coupler pins | 1 | $600 | $600 |
| Prototype System Total | ~$4,020 | |||
| Step | Action | Time |
|---|---|---|
| 1 | Position seastead over target using GPS/thrusters. Hold station. | 2 min |
| 2 | Attach pendant line to anchor. Lower anchor through guide until helix touches seafloor. | 3 min |
| 3 | Lower reusable drive shaft. J-slot coupler self-aligns and locks onto anchor post with ¼ turn. | 2 min |
| 4 | Run motor at ~20 RPM. Screw anchor ~7 ft into sand (6" pitch advances quickly). | 4 min |
| 5 | Reverse motor ¼ turn to unlock J-slot. Retrieve drive shaft. | 3 min |
| 6 | Tension pendant and secure to seastead's tension-leg hardpoint. | 3 min |
| Subtotal per screw | ~17 min | |
Total for all 3 screws including 5 min repositioning between legs: ~1 hour.
| Step | Action | Time |
|---|---|---|
| 1 | Slack tension leg. Leave pendant attached to anchor. | 2 min |
| 2 | Lower drive shaft and engage coupler. | 2 min |
| 3 | Reverse motor at ~20 RPM. Unscrew anchor while shaft provides upward pull. | 4 min |
| 4 | Disengage coupler. Retrieve drive shaft. | 3 min |
| 5 | Haul anchor up by its pendant line. | 3 min |
| Subtotal per screw | ~14 min | |
Total removal for 3 screws: ~45–50 minutes.
Target: 5,000–8,000 lbs working tension per screw | Water depth: up to 16 ft | Anchor: 12"Ø single helix, 12 ft shaft, ~10 ft embedment in sand.
| Component | Specs / Notes | Qty | Est. Unit Cost | Est. Total |
|---|---|---|---|---|
| Helical Anchor | SS316, 12"Ø helix (⅜" plate), 3" pipe shaft, 12' long, heavy welded mooring eye | 3 | $1,800 | $5,400 |
| Reusable Drive Shaft | SS316, 3" pipe, 18' long, heavy-duty J-slot coupler, splined motor flange | 1 | $1,800 | $1,800 |
| Electric Drive Unit | 22 kW 3-phase motor + 60:1 heavy planetary gearbox + VFD (380V), torque-limiting control | 1 | $2,500 | $2,500 |
| Heavy Gantry Frame | Steel A-frame with winch carriage, torque reaction beam, deck clamps | 1 | $1,200 | $1,200 |
| Mooring Pendants | ¾" UHMWPE (Dyneema), 25' length, heavy-duty thimbles, SS316 shackle/swivel | 3 | $280 | $840 |
| Alignment System | SS304 guide funnel + roller carriage to manage 18' shaft lateral loads | 1 | $400 | $400 |
| Shipping / Import / Misc | Freight, customs, spare coupler segments, torque sensor for VFD feedback | 1 | $2,200 | $2,200 |
| Full-Scale System Total | ~$14,340 | |||
| Step | Action | Time |
|---|---|---|
| 1 | Position seastead with GPS/thrusters. Hold heading against anticipated torque. | 3 min |
| 2 | Attach pendant. Lower 12' anchor until helix contacts seafloor (anchor top will be ~4 ft below surface). | 5 min |
| 3 | Lower 18' drive shaft through guide. Engage J-slot coupler onto anchor post. | 4 min |
| 4 | Run motor at 15–20 RPM. Screw anchor ~10 ft into sand. Monitor current draw to verify torque/capacity. | 10 min |
| 5 | Reverse motor to unlock. Retrieve drive shaft (winch assists the 18' shaft). | 5 min |
| 6 | Tension pendant with seastead winch or thruster pull; lock into tension-leg fitting. | 5 min |
| Subtotal per screw | ~32 min | |
Total for all 3 screws including 8 min repositioning between legs: ~1 hour 45 minutes.
| Step | Action | Time |
|---|---|---|
| 1 | Slack tension leg. Anchor remains attached to pendant. | 3 min |
| 2 | Lower drive shaft and engage coupler. | 4 min |
| 3 | Reverse motor. Unscrew ~10 ft while frame provides upward reaction. Sand release may require brief "bumping". | 10 min |
| 4 | Disengage coupler. Retrieve drive shaft. | 5 min |
| 5 | Winch anchor up to surface by pendant. | 5 min |
| Subtotal per screw | ~27 min | |
Total removal for 3 screws: ~1 hour 30 minutes.