Estimated Drag Coefficient (Cd)
Your legs are extremely thick — a true NACA 0030 (30% thickness-to-chord ratio). Most marine foils are 12–21% thick. At 30%, some flow separation is expected even at zero angle of attack.
Realistic Cd Estimate: 0.032 – 0.038
Referenced to planform area (chord × submerged height)
This is based on:
- Published data for thick NACA sections (NACA 0025–0030)
- Strut data from offshore platform design literature
- Allowance for real-world surface roughness and marine growth
- Reynolds number at 4–6 knots ≈ 6×10⁶ to 9×10⁶ (fully turbulent)
Note: A more optimized custom section (e.g. a modified NACA 00xx with aft loading or a "bulbous" leading edge) could reduce this to ~0.022–0.028.
Comparison to Round Cylinder of Similar Volume
| Parameter |
Wing Leg (NACA 0030) |
Equivalent Cylinder |
| Cross-section area |
21.9 ft² |
21.9 ft² |
| Equivalent diameter |
— |
5.28 ft |
| Frontal area (submerged) |
28.5 ft² (max thickness × height) |
50.2 ft² |
| Typical Cd (frontal reference) |
~0.55–0.65 (effective) |
0.75–0.85 |
| Drag at 4 knots (per leg) |
≈ 151 lbs |
≈ 1,710 lbs |
Result: The wing-shaped leg produces approximately 9% of the drag of a round cylinder of identical displaced volume at both 4 and 6 knots.
Drag Comparison at 4 knots (3 legs total)
Equivalent Cylinders (5,130 lbs)
Drag Calculations (Total for 3 Legs)
| Speed |
Dynamic Pressure (psf) |
Cd Used |
Total Drag (lbs) |
Power to Overcome Drag (hp) |
| 4 knots |
45.4 |
0.035 |
453 lbs |
≈ 4.9 hp |
| 5 knots |
70.9 |
0.035 |
708 lbs |
≈ 9.5 hp |
| 6 knots |
102.1 |
0.035 |
1,017 lbs |
≈ 16.4 hp |
Assumptions: 9.5 ft submerged height, 10 ft chord, seawater density 1.99 slugs/ft³,
planform area reference (10 ft × 9.5 ft per leg). Does not include wave drag,
stabilizer drag, or superstructure drag.
At cruising speeds of 4–5 knots, the three legs produce very manageable drag — easily overcome by
modest electric thrusters or even sail area. This aligns perfectly with your goal of abundant solar power.
Comparison to Similar Trawlers & Catamarans
Similar Displacement (~20–30 tons)
A conventional 40–50 ft trawler or cruising catamaran of similar displacement would typically have total resistance of:
- 800–1,600 lbs at 6 knots (depending on hull shape)
- Your 3 legs: 1,017 lbs at 6 knots
Advantage: Your design has almost no wave-making resistance thanks to the tiny waterplane area (SWATH-like behavior). A conventional hull at this speed is already generating noticeable waves.
Similar Length (80 ft platform)
An 80 ft displacement trawler or catamaran (typically 80–200 tons) at 6 knots (well below hull speed) would have total resistance in the range of:
Your leg drag of ~1,000 lbs at 6 knots is substantially lower, even before considering that your platform has far more usable deck space for solar panels.
Key Insight: This design gives you oil-platform levels of deck area and stability with trawler-level (or better) drag at low speeds. The combination of small waterplane area + streamlined legs is very efficient for solar-powered cruising.
Has This Been Done Before?
No — not in this exact configuration.
Elements exist in isolation:
- Semi-submersible oil platforms (large cylindrical or square columns)
- SWATH vessels (Small Waterplane Area Twin Hull) — mostly for high-speed ferries and research ships
- Some offshore platforms have had streamlined columns for current drag reduction
- Hydrofoil stabilizers and ride-control systems are used on fast ferries
However, the specific combination you describe appears unique:
- Triangular truss platform with railing integrated structure
- Three parallel NACA 0030 vertical legs at the vertices
- Small airplane-like stabilizers with servo-controlled elevators for trim
- Large solar-covered roof with central living pod and wrap-around porch
- Dinghy stored transversely behind the living structure in "wind shadow"
This is a clever synthesis of semi-submersible, SWATH, and multihull thinking optimized for maximum solar area with minimum propulsion power. It is genuinely novel for a seastead/liveaboard application.
Recommendations
- Consider a custom foil section rather than a pure NACA 0030 — a 25–28% thick section with a more gradual pressure recovery could reduce Cd by 20–30%.
- The 6 RIM-drive thrusters positioned 3 ft off the bottom are well placed for both propulsion and maneuvering.
- The small stabilizers with servo-assisted elevators are an elegant solution for controlling pitch and roll with low actuator forces.
- At these low speeds, total system drag (including the above-water structure in wind) will likely be 2–3× the leg drag. Still very manageable with electric propulsion and solar.
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