```html Seastead USV — 1:4 Scale Model Technical Analysis

Seastead USV — 1:4 Scale Model Technical Analysis

This document provides a complete engineering analysis of a 1:4 Froude-scaled unmanned surface vehicle (USV) model of the seastead trimaran design. It covers dimensions, weight budget, power systems, speed predictions, foiling potential, reliability, cost, competitive landscape, and sea-state survivability.

1 Froude-Scaled Dimensions (1:4)

Froude scaling preserves the ratio V / √(gL), so:

Lengths scale by 1/4
Areas scale by 1/16
Volumes & weights scale by 1/64
Speeds scale by 1/2
Time periods scale by 1/2

Parameter	Full Scale	1:4 Model
Triangle sides (left & right)	70 ft	17 ft 6 in
Triangle back (short side)	35 ft	8 ft 9 in
Triangle depth (front→back)	67.78 ft	16 ft 11 in
Triangle plan area	1,186 ft²	74.1 ft²
Frame height (truss)	7 ft	N/A — single solar layer
Leg length (vertical)	19 ft	4 ft 9 in
Leg chord (fore-aft)	10 ft	2 ft 6 in
Leg max width (beam)	3 ft	9 in
NACA section	0030	0030 (unchanged)
Leg draft (submerged)	9.5 ft	2 ft 4.5 in
Thruster diameter	1.5 ft	7.87 in (Blue Robotics M200)
Thruster position from bottom	3 ft	9 in
Stabilizer wingspan	12 ft	3 ft
Stabilizer chord	1.5 ft	4.5 in
Stabilizer body length	6 ft	18 in
Elevator span	2 ft	6 in
Elevator chord	6 in	1.5 in
Camera mast height	16 ft	4 ft
Full-scale weight	36,000 lbs	—
Model target weight (÷64)	—	562.5 lbs

  Note: The Blue Robotics M200 thruster (200 mm / 7.87 in) is slightly larger than the geometrically scaled 4.5 in. This is acceptable — the M200 is a proven COTS part and the extra diameter improves thrust at the cost of slightly more drag when idle.

2 Weight Budget

2.1 Non-Battery Components

Component	Qty	Unit Wt (lbs)	Subtotal (lbs)
Legs — 1/16″ 5083 marine Al skin + internal ribs (3)	3	25	75
Triangle frame — 1.5″ × 1.5″ × ⅛″ 6061 angle + cross supports	1 set	42	42
Stabilizer wings, bodies, elevators — Al sheet & tube (3)	3	3.3	10
Blue Robotics M200 thrusters	6	2.4	14
Electronics (Starlink Mini, RPi CM4, Navigator, ESCs, cameras, AIS)	1 set	—	16
Wiring, connectors, heat-shrink	1 set	—	8
Flexible ETFE solar panels	~60 ft²	0.5/ft²	30
Camera mast (1″ Al pipe, 4 ft)	1	3	3
LED navigation lights	1 set	—	1
Rescue system (rope, float, funnel)	1 set	—	4
Water brake (plate + hinge)	1	—	2
Stabilizer locking mechanisms (solenoid + pin, ×3)	3	0.7	2
Misc mounting hardware, brackets, sealant, potting compound	1 set	—	15
Non-Battery Subtotal			222 lbs

2.2 Battery Weight & Capacity

If batteries are 30% of total weight:

Total weight = 222 / 0.70 = 317 lbs (well below the 562.5 lb Froude target)
Battery weight = 317 × 0.30 = 95 lbs → ~3 × 12V 100Ah LiFePO4 batteries
Capacity ≈ 3 × 1,280 Wh = 3.8 kWh

  We have significant weight margin. The model is ~145 lbs lighter than the 562.5 lb target. We can load more batteries:

  5 batteries (155 lbs): 6.4 kWh — batteries at ~38% of total (377 lbs)

  6 batteries (186 lbs): 7.7 kWh — batteries at ~46% of total (408 lbs)

  9 batteries (279 lbs): 11.5 kWh — batteries at ~56% of total (501 lbs)

  Each leg can hold 2–3 batteries (internal volume ≈ 5.9 ft³ per leg; 3 batteries ≈ 3.6 ft³). 
  At a pack-level energy density of 41 Wh/lb (EVE LF280K cells + BMS + enclosure), 
  the sweet spot is probably 6 batteries = 7.7 kWh at ~408 lbs total.

2.3 Weight Summary vs. Budget

Scenario	Battery (lbs)	Battery (kWh)	Total (lbs)	% of 562.5 Target
30% battery	95	3.8	317	56%
Recommended (6 batteries)	186	7.7	408	73%
Max practical (9 batteries)	279	11.5	501	89%
Froude target	340	13.9	562.5	100%

Using the recommended 6-battery configuration (7.7 kWh, 408 lbs) for the rest of this analysis unless noted otherwise. Usable energy at 80% DoD = 6.2 kWh.

3 Solar Power System

3.1 Panel Recommendations

Option	Efficiency	Coating	Weight	Cost/W	Notes
Custom ETFE panels from China (SunPower Maxeon cells)	22%	ETFE	~0.45 lb/ft²	$0.60–0.80	Best fit. Can be cut to triangle shape. Splash-tolerant.
Renogy 175W Flexible	21%	ETFE	0.64 lb/ft²	$1.70	Rectangular only; ~80% fill in triangle.
SunPower Maxeon Flexible	22.8%	ETFE	0.46 lb/ft²	$2.50	Highest efficiency; rectangular; premium price.

Recommendation: Order custom-cut ETFE-laminated panels from a Shenzhen manufacturer using SunPower Maxeon or equivalent high-efficiency cells. The triangle shape lets you maximize coverage. Specify IP67 junction boxes and marine-grade MC4 connectors.

3.2 Solar Wattage

Configuration	Panel Area (ft²)	Peak Watts	Daily Energy (5.5 sun-hours)
Exact 1:4 scale (74.1 ft², 80% fill)	59.3	1,216 W	6,688 Wh
Exact 1:4 scale, custom panels (92% fill)	68.2	1,399 W	7,695 Wh
+5% enlarged triangle (81.6 ft², custom)	75.1	1,540 W	8,470 Wh

Recommendation: Expand the triangle ~5% in linear dimensions. This adds minimal weight (~4 lbs of angle) and gains 1,540 W peak / ~8.5 kWh per day. The extra solar is especially valuable for powering the Starlink and providing a night-time motor surplus.

3.3 Angle of the Solar Surface

A flat (horizontal) solar surface in the Caribbean at Anguilla's latitude (18°N) captures about 85–90% of what an optimally tilted panel would. For a USV that can't tilt toward the sun, flat is the right choice — and it minimizes wind loading.

4 Power Budget

4.1 Hotel (Base) Load

Device	Typical Draw (W)	Notes
Starlink Mini	30	25–40W range; averages ~30W in Caribbean
Raspberry Pi CM4 + IO Board	5	Moderate load (control, comms, vision)
Blue Robotics Navigator Board	1	Compass, IMU, 16 PWM outputs
6 × ESCs (idle / standby)	6	~1W each when powered but not driving
360° Camera (Insta360 X4)	5	Recording + streaming selected view
Raspberry Pi HQ Camera	3	Forward-looking, seaweed detection
AIS Class B Transceiver	3	Intermittent TX; em-trak B100 or similar
LED Navigation Lights (port, starboard, stern, mast)	3	COLREGS compliant
3 × Servo Actuators (stabilizer tails)	2	Intermittent
Misc (voltage regulators, temp sensors, etc.)	2
Total Hotel Load	~60 W

4.2 Available Motor Power

Using the +5% enlarged triangle with ~1,540 W peak solar:

Period	Solar Available	Hotel Load	Net for Motors + Charging	Motor Power Strategy
Peak sun (4–5 h midday)	1,540 W	60 W	1,480 W	Full speed + charge battery
Average daylight (12 h)	700 W avg	60 W	640 W	~400–500 W to motors, rest to charge
Night (12 h)	0 W	60 W	From battery	Battery provides motors + hotel

Steady-state 24-hour balance (no net battery change):

Daily solar: ~8,500 Wh
Daily hotel: 60 × 24 = 1,440 Wh
Available for motors: 7,060 Wh / 24 h = 294 W average

Day/night split:

Daytime (12 h): 400–500 W for motors, surplus charges battery
Nighttime (12 h): ~60–130 W for motors (from battery + solar surplus)

  Bottom line: With 7.7 kWh batteries (6.2 kWh usable), you have enough stored energy to motor at cruise speed for ~16 hours without any sun. In practice, the drone will charge during the day and cruise day and night.

5 Speed Performance

5.1 Drag Model

The primary drag source is the three submerged leg foils acting as surface-piercing struts. Using a blended approach (ITTC friction line + form factor + surface-piercing correction + appendages):

P_electrical ≈ 50 × V³ (Watts, V in m/s)

This includes ~40% motor/propulsive efficiency (M200 open propeller at moderate speed), 1.4× form factor for NACA 0030, 1.8× surface-piercing correction, and 1.3× appendage factor (stabilizers, thruster housings, brackets).

5.2 Speed Estimates

Scenario	Motor Power (W)	Speed (m/s)	Speed (knots)	Notes
Nighttime cruise (solar surplus limited)	60	1.06	2.1	Battery sustains this 12+ hours
Nighttime cruise (moderate battery)	130	1.37	2.7	Drains ~800 Wh from battery overnight
24/7 sustainable (solar only)	294	1.81	3.5	No net battery drain
Daytime cruise	400	2.00	3.9	Comfortable daytime speed
Daytime fast cruise	500	2.15	4.2	Surplus charges battery for night
Battery sprint	1,000	2.71	5.3	~6.2 hours on battery
Max burst (6 × M200 full)	2,520	3.69	7.2	~2.5 hours; use for storm evasion

Froude scale speed: A full-scale vessel at 8 knots corresponds to 4 knots model speed. The model achieves scale speed on solar alone during the day and can exceed it on battery.

5.3 Direction-Dependent Speed

Direction	Effect	Speed Modifier	Notes
Into wind / head seas	Wave resistance + wind drag oppose motion	−15 to −25%	Worst case; use extra battery
Beam seas	Roll increases wetted area; cross-current	−5 to −15%	Active stabilizers help resist roll
Following seas / downwind	Wind assists; possible surfing	+5 to +15%	Watch for broaching in steep seas
Calm / neutral	No wave or wind effects	Baseline

Typical Caribbean conditions (3–5 ft trade-wind seas): daytime cruise speed ≈ 3.0–4.0 knots depending on heading.

5.4 Endurance & Range Estimates

Mission Profile	Speed (kn)	Duration	Range (nm)	Notes
Infinite solar cruise (24/7)	3.5	Unlimited	~84 nm/day	Solar-sustained, no battery drain
Day fast / night slow	4.0 / 2.7	Unlimited	~80 nm/day	Solar balanced
Battery-only economy	2.7	~23 h	~62 nm	6.2 kWh usable, no solar
Battery-only sprint	7.2	~2.5 h	~18 nm	All 6 thrusters max; for emergencies
Typical daily patrol	3–4	12 h active	~40 nm	With idle overnight; fully solar-replenished

6 Foiling Analysis

The three stabilizer wings (3 ft span, 4.5 in chord, AR = 8) can be used as hydrofoils to partially or fully lift the vessel, reducing leg wetted area and drag.

6.1 Lift Requirements

Speed (kn)	Speed (m/s)	CL needed (full lift)	Feasibility
3.9	2.0	3.9	❌ Impossible — too high
5.8	3.0	1.73	⚠ Marginal — very high angle of attack