Water Pump Failure 35 Miles Offshore - Yanmar 4JH4E Breakdown & Discovery

While crossing the Mona Passage, 35 nautical miles offshore, we ran into trouble with our Yanmar 4JH4E. We were motoring in light winds when we noticed a change in the exhaust pitch - turns out, seawater wasn't flowing properly. We checked the impeller and, strangely, it looked intact? but it could spin freely by hand - not a good sign. After getting towed back to our anchorage at midnight (huge thanks to Michael, who came out and saved us!), we dug deeper and discovered that the gear inside the old water pump had worn down badly. It turns out the pump wasn't making full contact with the internal gear, likely due to an aftermarket impeller and shallow gear engagement. We ordered a new OEM water pump from R&B Power in San Juan, and they were awesome - super responsive and got us the part