Estimated Noise & Vibration from Submersible Mixers
This page provides rough engineering estimates for the underwater sound levels and vibration that may be generated by the four low‑speed submersible mixers (2.5 m diameter propellers) when the seastead is propelled at the speeds you listed (0.5 mph, 1 mph, and 1.5 mph). The numbers are based on typical published data for similar‑size, low‑speed mixers and on basic acoustic and vibration scaling laws.
Key assumptions
- Mixers are operated at a constant low speed that directly correlates with the platform’s forward speed (i.e., the propeller tip speed ≈ 0.5–1.5 mph). In practice the motor will turn slower than the free‑stream speed, but for a rough estimate we treat the propeller tip speed as the same order of magnitude.
- Sound power scales roughly with the 6th power of tip speed (a common “propeller‑noise” rule of thumb), giving about a 6 dB increase for each doubling of speed.
- Vibration at the motor mount is estimated from typical mixer‑motor assemblies (≈0.02–0.1 mm s⁻¹ RMS at low speeds). The 1‑inch rubber isolation layer reduces the transmitted vibration by roughly 10‑20 dB (i.e., a factor of ~3–10) depending on frequency.
- All sound levels are expressed in dB re 1 µPa at 1 m (the standard underwater reference). Vibration values are RMS velocities at the specified location.
Disclaimer: These are order‑of‑magnitude approximations. Real-world levels depend heavily on the exact mixer model, propeller design, motor bearings, mounting technique, water temperature, and ambient noise. Always obtain measured data from the equipment supplier and perform on‑site verification before finalising the design.
Estimated values
| Platform speed (mph) |
Typical underwater sound pressure level (dB re 1 µPa at 1 m) |
Vibration at motor mount (mm s⁻¹ RMS) |
Estimated vibration transmitted to platform (mm s⁻¹ RMS)
(with 1‑in rubber isolation) |
Qualitative observation |
| 0.5 |
55 – 60 dB |
0.02 – 0.03 |
≈ 0.002 – 0.005 |
Very quiet; comparable to a mild underwater murmur. Vibration barely perceptible. |
| 1.0 |
60 – 65 dB |
0.04 – 0.06 |
≈ 0.005 – 0.010 |
Low‑level hum, similar to a small river current. Vibration still modest. |
| 1.5 |
65 – 70 dB |
0.08 – 0.12 |
≈ 0.01 – 0.02 |
Noticeable but still well below levels that would cause discomfort. Vibration detectable only with sensitive instruments. |
How to use these numbers
- Noise: Underwater sound attenuates quickly with distance (≈ 6 dB per doubling of distance in free field). At a few metres from the mixer the levels will be far lower than the 1‑m values shown above. For comparison, normal conversation in air is roughly 60 dB SPL; underwater a 60‑dB signal is still relatively quiet.
- Vibration: The rubber mount already provides substantial isolation. If you need even lower transmission, consider adding a secondary resilient mounting (e.g., elastomer pads) and ensuring the mixer housing is not rigidly bolted to the steel leg.
- Human perception: Humans generally do not “hear” underwater sounds in the same way as in air, but many marine animals (fish, marine mammals) are far more sensitive. If the platform operates near sensitive ecosystems, the above levels are low enough to minimise behavioural impact, but you should still conduct an environmental noise assessment.
- Redundancy: Because you have four independent mixers, loss of one unit will only reduce the total thrust and increase the load on the remaining three. The acoustic and vibration contribution will drop proportionally (≈ 3 dB less for each mixer turned off).
Next steps
- Obtain the exact acoustic and vibration specs from the mixer manufacturer (most suppliers publish “sound power level” and “vibration amplitude” curves as a function of rpm).
- Measure the actual vibration transmission through the 1‑inch rubber layer using an accelerometer on a prototype leg.
- Consider adding a sound‑absorbing baffle or flexible hose between the mixer discharge and the leg to further reduce radiated noise if needed.
Feel free to embed this page directly into your project site. If you need more detailed calculations (e.g., exact thrust, power consumption, or a finite‑element vibration analysis), just let me know!