Deployment Notes: Tarakan Port, North Kalimantan, October 2023
The humidity hit us like a wall the moment we stepped off the skiff onto the quay at Tarakan. It was 0430 hours, and the air was thick, smelling of crude oil and salt. We were there to get a handle on the current vectors near the main berths, but the logistics were a nightmare. Tarakan isn't your typical deep-water port; it's a chaotic hub where massive coal carriers and petroleum tankers rub shoulders with nimble fishing boats in a tight, sediment-heavy environment.
The water state was deceptive. On the surface, it looked like a mirror, but the tidal flux in this part of North Kalimantan is aggressive. We were fighting a strong flood tide that pushed plumes of brown, silt-laden water from the surrounding mangroves right into the shipping channels. This high suspended sediment load is exactly why we were there—and why it's a headache for acoustics. Too much silt can choke a signal, but not enough gives you nothing to bounce off of. We were operating in that volatile middle ground.
What We Found
The data came back with a spike that stopped us cold: peak velocities hitting 1.2 m/s in the mid-water column during the spring tide transition. That's a lot of kinetic energy moving through a restricted channel. Most of the local pilots knew the current was strong, but they didn't realize how sharply the shear layer shifted. We saw a massive velocity drop-off in the bottom two meters, creating a shear zone that could easily push a drifting tanker's stern if the tugs aren't positioned perfectly.
Honestly, the most surprising part was the asymmetry between the ebb and flood. The flood tide surged in with a concentrated force, while the ebb drifted out in a more diffused, sluggish pattern. This suggests some complex bathymetric steering happening near the port entrance. We spent three hours ground-truthing the data against local tide gauges, and the correlation was tight, though the ADCP caught turbulence that the gauges completely missed. It's a reminder that 'average current' is a dangerous metric for a harbor master to rely on when docking a 50,000-ton vessel.
Equipment Performance
We deployed a bottom-mounted ADCP, and for the most part, it held its own. I was worried about bin contamination due to the heavy silt from the nearby river discharges, but the signal-to-noise ratio stayed acceptable. I'll be blunt: the 300kHz unit was the right call here. A higher frequency would have attenuated too quickly in this soup. We did see some noisy data during the peak flood—likely organic debris or schools of fish triggering false returns—but a quick manual filter cleaned that up. The mounting bracket stayed secure despite the current, which is a win given the unstable seabed composition in this region.
Recommendations for Future Deployments
If you're heading back to Tarakan or similar Indonesian ports, don't wing it. The sediment levels fluctuate wildly based on the monsoon cycle, which changes your acoustic window.
- Use a heavy-duty tripod with a wide footprint to prevent tilting in the soft, silty benthos.
- Set your blanking distance higher than usual to avoid 'ringing' from the seabed interface.
- Schedule deployments to overlap with both spring and neap tides; otherwise, your data is just a snapshot, not a profile.
- Bring extra desiccants for the electronics housing. The humidity in North Kalimantan eats gear for breakfast.
We spent the final evening watching the tankers maneuver into the berths. Seeing the current vectors on my screen while watching a ship fight a 1.1 m/s cross-current puts the physics into perspective. It's one thing to see a line on a graph; it's another to see a vessel leaning into the flow.
Field report by Capt. Marcus Thorne. Capt. Thorne is a specialist in maritime acoustics with 20 years of experience deploying hydrographic instrumentation in challenging tropical port environments.
Field Deployment Report: Bottom-Mounted ADCP Velocity Profiling at Tarakan Port