Seastead Prototype • Helical Mooring Screw Installation

Installation Method Overview

The helical mooring screws will be started by hand (a few turns), then driven to full depth using a 10 hp outboard dinghy. A rigid lever bar is attached to the eye of the screw. A rope from the end of the lever is pulled by the dinghy in a circular path, applying continuous torque to screw the anchor into the sand.

Assumptions: Typical Caribbean sand (medium density), single-helix anchors, 4-inch pitch, 10 hp outboard capable of sustained low-speed thrust. Times are estimates for active circling time (not including setup or repositioning).

Estimated Installation Times

6" diameter

22 min

Average time to 7 feet depth

Range: 15–30 minutes

12" diameter

52 min

Average time to 11 feet depth

Range: 40–70 minutes

Parameter	6" Helix (7 ft)	12" Helix (11 ft)
Estimated average torque	650–950 ft-lbs	2,200–3,400 ft-lbs
Number of revolutions	~21 revolutions	~33 revolutions
Dinghy thrust required	80–120 lbs	180–280 lbs
Difficulty	Easy	Moderate

Lever Bar Recommendations

6" Helix

Length	8 feet (96 inches)
Diameter	2.0 inch Sch 40 steel pipe
Weight	29 lbs
Lever arm	7.5 ft effective

Ideal for one person to handle. Provides good mechanical advantage for the smaller helix.

12" Helix

Length	12 feet (144 inches)
Diameter	2.5 inch Sch 40 steel pipe
Weight	70 lbs
Lever arm	11.5 ft effective

Longer bar recommended to reduce the force required from the dinghy. Consider two people for handling due to weight.

Connection Design (Critical Strength Point)

The end attached to the mooring eye experiences the highest stress. Standard pipe alone is insufficient at the connection.

Recommended connection:

Weld two ⅜" thick steel plates (3" × 6") on opposite sides of the pipe end
Drill ¾" or 1" aligned holes for a heavy clevis pin
Use a ¾" Grade 8 clevis pin with cotter pin
Reinforce with a ¼" gusset plate on the back side

Fabrication notes:

Galvanized pipe is ideal (corrosion resistance)
Make one custom bar per helix size
Cost to fabricate: ~$180–280 per bar at a local shop
Alternative: Use a heavy-duty tow bar or modified boat trailer tongue

Additional Recommendations

Safety & Efficiency Tips

Use a strong, low-stretch rope (3/8" or 1/2" double-braid)
Keep the dinghy at consistent speed to maintain even torque
Have a second person on the seastead to monitor the screw
Stop and check alignment every 2–3 feet of depth

Future Motorized Option

For regular use, consider a small hydraulic or electric torque motor mounted on the seastead that can be lowered to engage the screw eye directly. This would dramatically reduce installation time.

Recommended for production version