Concept: A slow-speed (4–5 knots) solar-electric displacement trawler utilizing actively controlled, underwater "gliders" (hydrofoils) on outriggers to provide roll damping and pitch/heave stability via variable lift.
While the physics of lift generation at 4–5 knots works, the system complexity, power budget impact, mechanical vulnerability, and tether management make this a high-risk R&D project rather than a viable product feature for a production boat. Active fins on the main hull (or a catamaran platform) are vastly superior solutions.
Recommended Path: Build a 1/4 scale RC model or retrofit a small existing powerboat (15–20ft) with surface-piercing sensor buoys first, before committing to submerged gliders.
For a 40–50 ft trawler (Displacement ~15–25 tonnes, Beam ~14–16 ft), the Righting Moment (RM) at 10° heel is roughly 150–300 kN·m.
To actively counter a beam sea induced roll acceleration (target: reduce roll amplitude by 50–70%), the gliders must generate a counter-moment comparable to 20–40% of max RM.
| Parameter | Estimate (40ft Trawler) | Estimate (50ft Trawler) |
|---|---|---|
| Displacement | 18,000 kg | 28,000 kg |
| Beam (B) | 4.5 m | 5.0 m |
| GMT (Metacentric Height) | ~1.2 m | ~1.5 m |
| Righting Moment @ 10° | ~215 kN·m | ~365 kN·m |
| Target Active Moment (30% RM) | ~65 kN·m | ~110 kN·m |
| Outrigger Lever Arm (Y) | 4.0 m (per side) | 5.0 m (per side) |
| Required Vertical Force / Glider (Fz) | ~8.1 kN (1,820 lbf) | ~11.0 kN (2,470 lbf) |
L = 0.5 * ρ * V² * S * CL
Required Wing Area (S) per Glider: S = Fz / (q * CL) = 8,100 N / (2,700 * 1.0) ≈ 3.0 m² (32 ft²) per side.
The actuator must move the tail fin (elevator) against hydrodynamic pressure to change the main wing Angle of Attack (AoA).
| Parameter | Value |
|---|---|
| Main Wing Area | 3.0 m² |
| Tail Volume Ratio (VH) | 0.5 (Typical for stability) |
| Tail Area (St) | ~0.6 m² (Total, both halves) |
| Tail Chord (ct) | ~0.35 m |
| Dynamic Pressure (q) | 2,700 Pa |
| Max Deflection (δ) | ±20° (±0.35 rad) |
| Hinge Moment Coeff (Ch) | ~0.006 / deg (balanced) to 0.015 / deg (unbalanced) |
Estimated Hinge Moment (per tail half): ~150 – 400 Nm.
You need high torque, low speed, absolute positioning.
| Technology | Pros | Cons | Est. Cost (Pair) |
|---|---|---|---|
| Direct Drive Rotary (Torque Motor) (e.g., T-Motor, Kollmorgen, custom) |
No gears/backlash; High reliability; Direct angle control; Can be pressure compensated (oil filled). | Large diameter (150–200mm); Heavy; Expensive magnets. | $8,000 – $15,000 |
| Harmonic Drive + Brushless Motor (HDSI, Nabtesco, Bayside) |
Compact; High reduction (100:1); Zero backlash; High torque density. | Requires pressure comp housing; Input shaft seal failure risk; Harmonic drives hate shock loads (slamming). | $5,000 – $10,000 |
| Linear Actuator (Pushrod) (Exlar, Thomson, Custom Hydraulic) |
Simpler sealing (single rod seal); High force native. | Side loading on rod = bent rods; Stroke length limits travel; Seal wear in ocean. | $3,000 – $8,000 |
| Hydraulic Cylinder (HPU on hull) | Infinite stall torque; Simple underwater unit; Proven marine tech (steering). | Requires hydraulic lines in tether (leak risk); HPU noise/power; Maintenance. | $4,000 – $7,000 |
Recommendation: Pressure-Compensated Direct Drive (Torque Motor) or Hydraulic. Electric gears/seals at 2–3 bar (20–30m depth) + shock loads from waves = high failure rate. Pressure compensation (oil-filled motor housing with diaphragm) eliminates seal friction and pressure differential.
This is the single hardest engineering problem. The tether must survive:
Core: High Modulus Polyethylene (Dyneema/Spectra) or Carbon Rod (Structural)
Power: 2x 12 AWG (or 10 AWG for 48V @ 20A) - Oil resistant TPE insulation
Data: 2x Shielded Twisted Pair (Cat5e/6 equiv) or Fiber Optic (2 fibers)
Jacket: Polyurethane (PUR) or Neoprene - Abrasion resistant, neutrally buoyant
Diameter: 25–35 mm (1 - 1.4 inches)
Weight in Air: ~0.8 - 1.2 kg/m
Buoyancy: Must add syntactic foam fairings or buoyancy modules every 2-3m to prevent catenary drag/snag.
$150 – $300 / meter (Custom marine umbilical). For 15m deployed length x 2 sides = $4,500 – $9,000 just for cable. Connectors (SubConn / Seacon) = $500–$1,500 each end.
P = D * V
Glider Drag (D) = Lift (L) / (L/D ratio). Underwater foils at Re ~ 1.5M achieve L/D ≈ 20–30 (clean). With struts, tether fairings, junctions: System L/D ≈ 8–12.
| Item | Value (Per Glider) |
|---|---|
| Lift Force (Vertical) | 8,100 N |
| Induced + Profile Drag (L/D=10) | 810 N |
| Strut / Tether Drag (Est.) | 400 N |
| Total Drag / Glider | ~1,210 N |
| Speed | 2.3 m/s |
| Mechanical Power / Glider | ~2.8 kW |
| Total Mechanical Power (2 Gliders) | ~5.6 kW |
| System Efficiency (Prop/Gen/Motor ~0.7) | ~8.0 kW Electrical |
// Simplified PID / LQR Loop running at 50-100Hz on Hull Computer (ROS2 / Simulink) Target_Roll_Rate = 0; // Stabilization goal Error = Measured_Roll_Rate - Target_Roll_Rate; // Feedforward: Wave Spectra Estimation (Kalman Filter on Hull IMU) // Feedback: Glider IMU (AoA, Roll Rate) Commanded_Lift_Port = Kp * Error + Kd * d(Error)/dt + FF_Wave_Estimate; Commanded_Lift_Stbd = -Commanded_Lift_Port; // Mixer: Convert Lift -> Tail Fin Angle (via Glider Local Controller) // Glider Local Loop (on Glider MCU): // Measure AoA -> PID -> Motor Torque -> Tail Fin Angle // Safety: Hard limit AoA < Stall_Angle (12-15 deg) // Safety: If Tension < 500N -> Neutral Fins (Feather)
If the glider stalls (AoA > 15°) due to a wave slam or control glitch, lift vanishes instantly. The 10kN tension drops to drag-only (~1kN). The glider plunges. Recovery requires the wing to regain flow attachment at 4 knots—slow. If it spins, the tether wraps the strut/outrigger.
A 3m² wing at 2m depth is a perfect net for logs, crab pots, kelp, fishing nets. Impact load >> Design load. Shear pins/fuse links required on outrigger attachment.
You cannot enter a marina with 4m outriggers and 15m tethers deployed. Retraction mechanism (winch + folding wing) adds massive weight/complexity/volume.
Glider draft = Hull Draft + Strut Length (2–3m). Limits cruising grounds significantly.
Outriggers > 2m width require day/night shapes (black balls/diamonds) and lights. Tethers are invisible hazards to props of other vessels.
| Solution | Power @ 4kts | Complexity | Effectiveness | Cost |
|---|---|---|---|---|
| Active Hull Fins (Stabilizers) (Wesmar, Naiad, CMC, Quantum) |
0.5 – 1.5 kW (Electric) / Hydraulic off engine | Low (Inside hull) | Excellent (Roll) / Good (Pitch) | $40k–$100k |
| Gyro Stabilizers (Seakeeper, VEEM) |
1–3 kW (Electric, constant) | Medium (Heavy flywheel) | Excellent (Roll only, Zero speed) | $50k–$150k |
| Interceptors / Trim Tabs (Humphree, Zipwake) |
< 100 W | Very Low | Good (Pitch/Heave/Trim) / Fair (Roll) | $15k–$40k |
| Catamaran / SWATH Hull | 0 kW (Passive) | Naval Arch only | Best Passive Stability | Hull Cost Premium |
| Passive Paravanes (Flopper Stoppers) | 0 kW (Drag penalty ~0.5 kt) | Low (Mechanical) | Good (Roll only, Fixed) | $5k–$15k |
Recommendation for Solar Trawler: Electric Active Fins (Retractable) + Large Interceptors on transom. Fins handle roll; Interceptors handle pitch/trim/heave. Both fit inside hull lines, zero snag risk, low power, proven tech.
Compare measured Roll Reduction % vs. Measured Power Cost vs. Commercial Fin Specs. Expect result: "Active Fins Win."
The "Active Paravane Glider" concept is a fascinating Control Systems / Robotics PhD thesis, but a poor choice for a Commercial Family Solar Trawler Product.
Design the boat for Retractable Electric Fins + Interceptors. Use the roof space saved from "Glider Garage" for more Solar Panels → More Range → Better Product.