Persona Adopted: Senior R&D Mechanical Engineer (Marine Systems & Prototyping)
Abstract
This technical review analyzes the iterative development and field testing of a 25-horsepower Diver Propulsion Vehicle (DPV) designed for high-velocity underwater transit. The project progressed from a baseline performance of 11.3 km/h to a peak velocity of 18 km/h, utilizing computational fluid dynamics (CFD) and hardware optimization. Key engineering hurdles addressed include hydrodynamic drag reduction through teardrop-shaped 316L stainless steel motor mounts, electronic speed controller (ESC) calibration to bypass power-limiting safety protocols, and the fabrication of counter-rotating propellers via photogrammetry and resin 3D printing to neutralize rotational torque. Final testing in Croatia and controlled environments identified critical physical and mechanical limitations, specifically regarding barotrauma to the operator's ears and material failure under high-torque loads. While the project fell short of its 25.2 km/h "mako shark" benchmark, it successfully demonstrated the efficacy of rapid prototyping in improving DPV efficiency.
Building An Underwater Human Rocket: Technical Summary
0:00 Project Objectives: The development team aimed to construct a 25-horsepower underwater propulsion system to exceed the top swimming speeds of sharks (targeted at 25.2 km/h).
1:24 ESC Software Optimization: Initial failures at high power (Mode 4) were traced to Electronic Speed Controller (ESC) software limitations. Recalibration "unlocked" the power mode, establishing an initial baseline speed of 11.3 km/h.
3:06 Hydrodynamic Drag Analysis: CFD analysis using Airshaper identified four primary drag sources: handles, motor mounts, motor hubs, and the human operator. The operator accounted for 78 kg of drag, while the vehicle components accounted for 53 kg.
5:16 Structural Redesign: To minimize the drag coefficient, the team redesigned the vehicle to align the operator more closely with the tube. Motor mounts were thinned and fabricated using 316 stainless steel metal 3D printing to maximize strength-to-volume ratio.
7:21 Performance Gains from Aero/Hydro-Optimization: Post-redesign simulations showed a 50% reduction in total drag, resulting in a recorded speed of 13 km/h (3.7 m/s).
9:15 Thrust Discrepancy & ESC Failure: Bench testing revealed that intelligent VESC units were limiting thrust to 30 kg per motor. Switching to "unlimited" cheap ESCs increased thrust to 60 kg per motor (120 kg total) but resulted in thermal runaway and component combustion.
12:33 Torque Neutralization: The use of identical propellers caused the vehicle to rotate on its longitudinal axis due to reactive torque. The team utilized photogrammetry to create a mirrored 3D model, then printed a left-hand propeller using a Form 4 resin printer and "Tough 2000" material.
15:13 Field Testing & Physiological Limits: Testing in Croatia revealed that velocities exceeding 15 km/h caused significant ear pain (pressure-related discomfort) for the operator. Mechanical failures included a snapped resin propeller and an expensive ESC malfunction.
17:33 Mitigating Barotrauma: A water polo helmet was introduced to provide ear protection, allowing the operator to withstand higher velocities without immediate physical distress.
18:26 Final Performance Benchmark: The final optimized run achieved 18 km/h. The team concluded further speed increases were restricted by safety concerns and the physical limits of human endurance underwater.