Here's the analysis wrapped up as a standalone HTML page you can drop straight into your site: ```html Dinghy-Driven Helical Mooring Screws — Time, Torque & Lever-Bar Sizing

Dinghy-Driven Helical Mooring Screws

Installation time, torque, and lever-bar sizing for a 10 hp dinghy circling method — typical Caribbean sand bottom.

1. Quick answers

	6″ single helix → 7 ft deep	12″ single helix → 11 ft deep
Time per screw	~20 min (range 15–30)	~45 min (range 35–70; more in dense sand)
Peak install torque	250–450 ft-lb	1,800–3,000 ft-lb
Recommended bar	pick 10 ft × 1.5″×1.5″×3/16″ 6061-Al square tube alt 10 ft × 1.5″ Sch 40 galv. pipe	pick 12 ft × 3″×3″×3/16″ 6061-Al square tube alt 12 ft × 3″×3″×1/4″ 6061-Al (if dense sand expected)
Bar weight	~12 lb (Al) / ~27 lb (steel pipe)	~30–39 lb (Al) / ~86–91 lb (steel — not recommended for dinghy handling)
Longer bar for big helix?	No — 10 ft is plenty (torque demand is tiny)	Yes — 12 ft (vs 10 ft) cuts rope pull ~17%; beyond ~14 ft handling and circle time hurt
Reinforced eye end	Optional (light duty)	Yes — fork + cross-bolt + sleeve plug, adds only 4–6 lb

2. How the circling method works (and its limits)

Two simple relations govern everything:

Torque available ≈ (usable thrust) × (radius R of the dinghy's circle)
Rope tension F = T ÷ (L × sinθ) (L = bar length, θ = rope-to-bar angle, keep θ ≈ 90°)

A 10 hp outboard: ~250–300 lb bollard pull; plan on 150–220 lb usable while circling under load.
6″ screw case: R ≈ 22 ft → torque ceiling ~4,000 ft-lb vs. ~450 needed. Thrust-rich — you're limited only by how fast you want to spin it.
12″ screw case: R ≈ 28 ft → ceiling ~5,000 ft-lb vs. ~2,500 needed — OK, but rope tension F = 2,500/(12×0.8) ≈ 260 lb, right at the practical limit for a 10 hp rig. This is why the 12″ job is slower and margin is thin.

Steady-state geometry. A bigger orbit (R) buys torque but costs time per revolution; a longer bar (L) keeps rope tension low. The rotating pull averages out sideways loads, which helps the screw stay plumb.

3. Expected installation torque (medium-dense carbonate sand, φ ≈ 30–34°)

Screw	Avg. torque over run	Peak torque (at final depth)
6″ helix → 7 ft	150–250 ft-lb	250–450 ft-lb
12″ helix → 11 ft	800–1,500 ft-lb	1,800–3,000 ft-lb

Caribbean caveat: carbonate/shelly sand varies a lot. Loose carbonate sand installs easier than these numbers; dense or shelly layers can add 50–100%. Probe each spot first (hook off the dinghy or a quick dive) for coral heads before committing.

4. Time estimates

6″ × 7 ft → ≈ 20 minutes per screw (15–30)

Revolutions: 84 in ÷ 3 in pitch = 28 revs
Hand-start first ~2 ft (8 revs, in the water or over the gunwale): 8–12 min
Rope phase: 20 revs at R ≈ 22 ft, ~4 mph → ~2.5 rpm → 8–12 min

12″ × 11 ft → ≈ 45 minutes per screw (35–70)

Revolutions: 132 in ÷ 4 in pitch = 33 revs
Hand-start first ~2 ft (diver-assist recommended — see §8): 10–18 min
Rope phase: ~27 revs at R ≈ 28 ft, ~3 mph → ~1.5 rpm → 18–25 min
+20–40% allowance for stalls (backing off ¼ turn and re-advancing)

Budget note: a full mooring is 6 screws (2 per corner × 3 corners) → roughly 2–3 hours of screw time for the prototype, 4–6 hours at full size. That's very feasible with the dinghy method — and confirms your plan for a motorized driver later (only ~2.5–5 hp at 5–10 rpm is needed for 2,500 ft-lb).

5. Lever bar selection

The bar root (at the eye) carries the full torque in bending — the moment tapers linearly to zero at the tip. Sizing rule: section modulus S ≥ T×12 / 20,000 (20 ksi working stress).

For the 6″ screw (design M = 5,400 in-lb)

Bar (10 ft)	S (in³)	Stress	Safety factor	Weight
1.5″×1.5″×3/16″ 6061-T6 sq tube pick	0.38	14.1 ksi	2.5	~12 lb
1.5″ Sch 40 galvanized pipe alt	0.33	16.6 ksi	2.2	~27 lb
1.25″ solid steel square	0.33	16.6 ksi	2.2	~53 lb — avoid

For the 12″ screw (design M = 30,000 in-lb)

Bar (12 ft)	S (in³)	Stress	Safety factor	Weight
3″×3″×3/16″ 6061-T6 sq tube pick	1.86	16.1 ksi	2.2	~30 lb
3″×3″×1/4″ 6061-T6 sq tube margin	2.33	12.9 ksi	2.7	~39 lb
3″ Sch 40 steel pipe	1.72	17.4 ksi	2.1	~91 lb
3″×3″×3/16″ steel sq tube	1.86	16.1 ksi	2.2	~86 lb

Hollow square tube beats solid bar — far more strength and stiffness per pound; solid bar is what makes typical "digging bars" so heavy for their strength.
Stepped/tapered bars were evaluated and aren't worth it here: although bending moment tapers toward the tip, larger thinner-walled tube is more weight-efficient per section modulus than a stepped small-tube/large-tube combo. Uniform section wins.
One-bar option: a single 12 ft × 3″×3″×3/16″ 6061 tube (~30 lb) handles both screws if you want a minimal kit.
Aluminum vs steel: 6061-T6 is the right call for boat handling (1/3 the weight, ample strength). Rinse with fresh water; use 316 stainless through-bolts.
End fittings: fork + cross-bolt at the eye (§6); 3/8″ shackle hole plus a bolted-on 18″ T-handle at the tip; depth marks every foot; a lanyard/float so a dropped bar isn't lost.

6. Reinforced eye end — off-the-shelf or build?

Your instinct is correct: the eye end is the critical section (full torque in bending, regardless of bar length). There is no standard catalog bar with a reinforced end suited to this duty — breaker bars are too small, digging bars are solid and heavy, torque-wrench extensions are uniform. Nearest useful raw stock: A500 square tube plus a 2″ trailer-receiver tube section for the fork. Making one is very reasonable — a weld shop needs about an hour, or build it bolted with no welding at all:

Build A — bolted (best for aluminum, field-repairable): cut a fork