This Pololu discussion is useful here. It describes a nearly identical Raspberry Pi problem. Measuring voltage at several points. Measure both converter output and Pi input. This reveals where the voltage actually drops. Pololu also mentioned capacitors for brief transients. The case in the old thread ultimately involved cable and plug quality. That makes your connectors worth investigating carefully. This Electrical Wire Connectors Types guide helps. It covers contact resistance, crimping, ratings, and vibration. Your boat environment makes those factors especially important. I would test directly at the Pi’s USB-C. Then compare readings under identical network loads
