Captain's Log, Supplemental: Under Tow

We are anchored in St. Marys, Georgia where we were towed in yesterday after both engines overheated in an uncanny show of solidarity—first the starboard, and when I went to the engine room to check it, the port engine followed its twin's lead.

This morning, I spoke to Brian at American Diesel, who immediately identified the issue and talked me through the recovery. Eventually, I will be making a modification to the engines to prevent a recurrence, but for now, we have a working pair again, and the knowledge for preventing the issue in the future. 

Saturday we ran in rough conditions approaching St. Andrew Sound. Wind was out of the NE and started bashing us as we came around the bend approaching Brickhill River. Rather than turn the inside of the boat into a hunt for all the flying fruit and spuds from our hanging baskets, I spun us on our heel and backtracked about 4 miles to anchor out of the fetch.

Winds pegged our anemometer at 61 MPH—the same winds driving the rough seas.

In the morning, we overheated after being underway only 3 or 4 minutes. We re-anchored nearby in a very conveniently placed spot just deep enough for us west of the ICW red markers.  Coolant was everywhere, but I could not pinpoint the source. It was coming from around the caps—which always belch a little anyway—and from the weep holes. The combination made for an indeterminate point of failure.

The rough seas evidently whipped the usually harmless air from high in the expansion/header tanks into the cooling loops, aerating the coolant as it circulated. Overnight, as the engines sat, those millions of tiny bubbles buoyed up and coalesced at the high point of both engines—in the water-cooled exhaust manifolds—forming a localized airlock. Because the overflow ports are salted solid, the systems had no proper expansion path (There is a fix for that which I am now aware of—a modification to the expansion tanks to include a properly designed overflow path. It's a job for another day).

Once underway yesterday, that trapped air gave way to steam. Since steam expands exponentially, it spiked the pressure beyond allowable thresholds, forcing coolant out of every available pressure-relief orifice. The temperature sensors, located near that high point, triggered the alarms and pegged the gauges.

Refilling the expansion tanks while the bleeder valves at the manicooler high points were open successfully purged the trapped air. We have now had a successful run of both engines. We're back in the saddle!