Seastead Submersible Mixer Noise & Vibration Estimates
Design Context: 4 low-speed submersible mixers with 2.5m diameter propellers mounted near the bottom of 4ft-wide duplex stainless steel legs/floats. Platform speed driven by solar power. 1-inch thick tire-like rubber isolation layer between floats and main body. Additional vibration isolation mounting recommended (e.g., flexible couplings, damped motor mounts).
Estimated Performance at Target Speeds
| Speed (MPH) |
Est. RPM per Propeller |
Est. Tip Speed (m/s) |
Underwater Noise (dB re 1 μPa @ 1m) |
Vibration Transmission (RMS acceleration @ platform) |
Notes |
| 0.5 |
4-8 RPM |
~1.0-2.0 |
80-90 dB (very quiet) |
<0.005 g (negligible) |
Minimal power (~50-100W total). No cavitation. Comparable to quiet ambient ocean noise (70-90 dB). |
| 1.0 |
8-15 RPM |
~2.0-3.8 |
90-100 dB (low) |
0.005-0.02 g (low) |
Low power (~200-500W total). Rubber isolation reduces transmission by 90%+. Still below marine mammal hearing thresholds for extended exposure. |
| 1.5 |
12-25 RPM |
~3.0-6.3 |
100-110 dB (moderate) |
0.02-0.05 g (moderate) |
Higher power (~500-1000W total). Potential for minor turbulence noise. Vibration isolators essential; expect comfortable levels with rubber + damping. |
Key Assumptions & Methodology
- RPM/Tip Speed: Estimated for ~125-500N thrust per propeller (total drag ~500-2000N based on ~50x74ft platform footprint, Cd≈1.2-1.5, low-speed viscous drag dominant). Assumes efficient low-pitch mixer propellers (pitch ratio ~1.0-1.5).
- Noise: Based on empirical data for large low-speed marine propellers (Ross propeller noise models, submersible mixer specs). Scales with ~50 log(P) + 20 log(D) + tip speed effects. No cavitation expected (<10 m/s tip speed).
- Vibration: RMS acceleration at platform deck, post 1" rubber isolation (isolation efficiency ~20-40 dB). Raw motor/prop vibration ~0.1-0.5g at hub, reduced by rubber/flex mounts. 4 props distributed reduces coherence.
- Background ocean noise: 70-100 dB. Levels are 1/3-octave band summed, dominated by low frequencies (<500 Hz).
Disclaimer: These are engineering estimates based on standard hydrodynamic/acoustic models and typical submersible mixer data (e.g., Flygt, ABS mixers). Actual values depend on exact propeller design, balance, mounting, water conditions, and hull drag. Recommend prototype testing with hydrophones and accelerometers. Noise/vibration can be further reduced with variable frequency drives (VFD), shrouded nozzles, or polymer propeller coatings.
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