Our normal tide at this point along the Maine coast is about 10 feet. There was no unusual tidal fluctuation then. I have certainly seen some huge waves here, much bigger than the two we encountered but only when a hurricane is moving up the coast and they are never isolated like these two were.
Things were "flat calm" and two waves appeared. It was bad luck that we were were we were but good luck that we were not a little farther out over the ledge when the first wave rose up. My first thoughts were that it was caused by the wake from a ship that got funneled into the ledges by the underwater contours. The 50 fathom line does converge just off the the ledges. The contours form a general 90 degree corner at the ledges with the sides of the angle extending East and South.
Waves are curious. Paying attention to the underwater contours has become standard for me now. We do have many serious tidal rips along our coast. Some are marked on the charts and should be taken very seriously especially when wind and tides are contrary. "The Old Sow" is a huge whirlpool at the entrance of Passamaquoddy bay and I have been through it many times. I have also been through the "gut" at East Bunker Ledge many times and never have seen that wave action before or since.
It made for an interesting day! That little boat is amazing.