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TRIAD-1 settles onto three helical-screw pairs and goes taut-leg, like a small compliant TLP. The open question on this sheet: what winch quietly pays out and takes in the tension legs as the tide breathes — 2,000–3,000 lbs today, bigger water later? The hydrostatics, the duty cycle, and the hardware verdict are below, with a live sizing calculator in the Winch Lab.
Use a self-locking, slow drive — never a fast planetary winch. Phase 1 (Caribbean, ≤ 4 ft tides): a motorized ACME screw-jack tensioner at each corner — silent, millimeter-precise, holds dead-still with zero power. Phase 2 (bigger tides): a worm-gear drum winch, or a traction capstan for unlimited payout. Because the tide only moves a few feet per hour, the whole job takes tens of watts.
Pulling the platform down by d feet submerges more of the three struts. Extra buoyancy appears, and the tension legs have to eat all of it. Per your numbers, each foot of sink adds ~1/7 of the 27,500 lb rating:
| PULL-DOWN | TOTAL UP-FORCE | PER LEG (STATIC) | PER LEG ×2 WAVE FACTOR |
|---|---|---|---|
| 0.5 ft | 1,964 lbs | 655 lbs | 1,310 lbs |
| 1.0 ft | 3,929 lbs | 1,310 lbs | 2,620 lbs |
| 2.0 ft | 7,857 lbs | 2,619 lbs | 5,240 lbs |
| 3.0 ft | 11,786 lbs | 3,929 lbs | 7,860 lbs |
| 4.0 ft | 15,714 lbs | 5,238 lbs | 10,480 lbs |
BARS ANIMATE ON SCROLL · 12,000 LB SCALE
Think of it as a giant powered turnbuckle between the deck and the mooring line. A stainless Acme screw, a bronze nut, and a worm-geared motor — geared so far down that the screw turns ~10 rpm. It is the quietest, most precise, and most fail-safe way to move 3,000 lbs an inch at a time.
The tide is a slow sinusoid: peak vertical speed ≈ 0.25 × range ft/hr. A 3-ft Caribbean tide crests near 0.75 ft/hr — 0.012 ft/min. So this winch almost never moves, must hold perfectly when it stops, and must be quiet enough to sleep next to. That profile kills most winch families and makes the slow, self-locking ones shine:
Self-locking Acme screw + worm gearmotor. Holds tension indefinitely with zero power and zero heat. Silent at 10–15 rpm — mostly you’ll hear water. Stroke is limited to screw length (~3–6 ft practical), which is exactly the Phase-1 requirement. Machine-screw-jack manufacturers (Joyce, Power, Duff-Norton class, 5–10 ton) supply the core; add 316SS screw, marine seals, grease packing, and anodes.
Same self-locking, same quietness, but line storage on a grooved drum with a level-wind. Drum sized for the tidal range (range × 1.25 + working margin). This is the classic “slow boat” drive — enormous reduction in two worm stages, and a natural upgrade path: keep the screw unit for fine trim and let the drum take the long stroke. Dutton-Lainson-style worm winches make decent prototype mules; production units should be stainless/bronze and sealed.
The line passes straight through gripping wheels — unlimited payout in a small package, the trick sailing-industry traction winches (Harken Industrial et al.) already do quietly in aluminum. Tail goes to a storage bin with light tail tension. This is the answer for the UK/France coast or anywhere Fundy-adjacent, and it never runs out of drum.
Fast, cheap, loud, and not self-locking — the brake does the holding, which means wear, heat, and a slow creep risk on a months-long set. High-rpm motor whine next to the berths ends the discussion.
Superb control and hold (valve-closed), but you inherit an HPU’s hum, hoses, and leak paths on a living platform — for a job a 50-watt screw does. Save hydraulics if a future seastead needs 20-ton tensioning.
Pawl clatter is the opposite of the brief, chain weight fights your light-displacement philosophy, and a chain catenary can’t pre-tension a taut leg anyway.
Each corner winch hangs off the seastead’s existing computer and its leg’s battery/inverter bus — same triple-redundant topology as the thrusters. Feedforward from a tide table (harmonic constants for the anchorage, or a deck-mounted pressure tide gauge) does 95% of the work; the load cell trims the last few percent.
| TIDAL RANGE | TYPICAL WATER | RECOMMENDED DRIVE |
|---|---|---|
| 0–4 ft | Anguilla · most Caribbean anchorages | CLASS A — ACME screw tensioner, 3 ft stroke |
| 4–15 ft | Bahamas banks edges · US East Coast · N. Spain | CLASS B — worm-gear drum + screw for fine trim |
| 15 ft + | UK · France Atlantic · Bay of Fundy | CLASS C — traction capstan (unlimited payout), or staged re-shackling + screw |
Peak tide speed ≈ 0.25 × range ft/hr (semi-diurnal sine). Recommended line speed carries a 4× margin and a 0.25 ft/min floor for setup work. Power assumes ~30% end-to-end drivetrain efficiency (worm or Acme).
Motorized ACME screw tensioner handles this with room to spare.
| REV | PHASE | NOTES |
|---|---|---|
| A | CONCEPT | Container-packing geometry locked: 44′ triangle, 21′-6″ legs, nested-foil stowage. |
| B | HYDROSTATICS | Waterplane stiffness ≈ 3,929 lbs/ft; per-leg tension table; wave factor policy set. |
| C | TIDE-TRIM DRIVE | Winch selection (this sheet): ACME screw-jack Phase 1 → worm drum Phase 2 → traction capstan for mega-tides. Load-cell + tide-feedforward control on existing per-leg buses. |
Figures are design estimates from the stated hydrostatics (27,500 lb rating; 1 ft ≈ 1/7 of buoyancy) and standard semi-diurnal tide kinematics. Confirm mooring holding capacity, leg scantlings, and tension-leg fatigue with a qualified naval architect / mooring engineer before crewed occupancy.