The day we drove out to take pics of the shack at the marsh, we also stopped by Joe's Lobster & Fish Mart at the Sandwich Marina. As we pulled into the lot, a tug was bringing a huge barge into the Canal so I leapt out of the car and was able to get a few pictures before it went by. It was extreme high tide and was running west with the ships. This can be dangerous because the current is pushing from behind.
We left the shop and headed back home. As we crossed the Sagamore Bridge, the tug & ship had just gone underneath and for a brief time we were traveling alongside it on our side of the Canal, but I got to BBay first. We decided to go right to the park and wait for it to pass us. We just got to the edge of the Canal and there it was, going under the Bourne Bridge.
The tug was using as much of the Canal as possible because that barge would start to drift too far to one side or the other because the swift current was pushing it. Apparently a few years ago, a barge grounded on the rip rap under similar conditions.