Deployment Notes: Funchal Harbor, Madeira, September 2023
The Atlantic wind was ripping across the quay when we stepped off the vessel at dawn. Madeira Port—specifically the Funchal harbor area—is a deceptive piece of water. On the surface, it looks like a serene deep-water refuge for cruise liners, but the bathymetry here is aggressive. The harbor sits against a volcanic backdrop where the seabed drops off precipitously. This creates a nightmare for current modeling because you have deep-ocean swells pushing into a constrained port geometry, often resulting in unpredictable shear layers that can toss a medium-sized cargo ship off course during docking.
The water was a clear, piercing blue, but the salinity gradients were shifting. We were operating in a window where the North Atlantic Current interacts with local coastal eddies. It was humid, the air thick with the smell of salt and diesel from the nearby refueling berths. Visibility was high, but the current was already pulling hard toward the open sea, making the initial deployment of the tripod frame a fight against the tide.
What We Found
The most striking data point came from the first 48 hours of velocity profiling: we caught a massive shear event just 10 meters above the seabed. While the surface currents were relatively sluggish, the bottom layers were surging in a completely opposite direction. This kind of vertical decoupling is common in volcanic basins but rarely documented with this precision in Funchal. It explains why pilots often report "strange" handling characteristics when maneuvering cruise ships near the berths; the hull is essentially being pushed by two different water masses simultaneously.
I noticed some significant noisy data in the lower bins during the peak tide. After a quick sanity check of the raw backscatter, it wasn't instrument failure—it was sediment transport. We're seeing an influx of organic debris and volcanic silt being swept along the bottom. This creates a "cluttered" signal. However, the core velocity vectors remained solid. We saw peak flow speeds that exceeded our initial estimates by nearly 20%, particularly near the channel edges where the flow compresses. It's a volatile environment.
Equipment Performance
We ran a 300kHz ADCP for this stint, and honestly, it was the right call. A higher frequency unit would have lacked the range to capture the full water column in the deeper sections of the port, and we would have suffered from too much bin contamination near the surface. The unit held its position on the seabed despite the surge, though the mounting bracket took a beating from the debris. The Doppler shift calculations were clean once we filtered out the sediment noise. I've seen these units struggle in high-turbidity estuaries, but the Atlantic water here is clear enough that the signal-to-noise ratio stayed well within my comfort zone.
Recommendations for Future Deployments
If we go back to Funchal, we need to change the sampling interval to catch the higher-frequency oscillations of the internal waves. I'd also suggest a multi-point array to map the lateral extent of those shear layers.
- Switch to a 15-minute averaging window to better resolve tidal transitions.
- Use heavier ballast for the tripod to prevent "creep" during storm surges.
- Deploy a secondary CTD sensor to correlate velocity spikes with salinity shifts.
- Increase the blanking distance to avoid surface noise from cruise ship propellers.
Field report by Dr. Alistair Vance. Dr. Vance is a specialist in underwater acoustics and salt wedge modeling with twenty years of experience in deep-water instrumentation.
Field Deployment Report: Bottom-Mounted ADCP Profiling at Madeira Port