Hi Michael--
I wouldn't think a wood lifeboat would last long under those conditions either, which is why I posted the question. I am a complete novice to the ins and outs of sonar and I realize that with sonar all is not always as it seems, but those some of those shapes look pretty darn convincing--and interestingly, they don't seem to show up further aft or in the forwardmost boat positions.
You mention that the shapes are too low on the superstructure, but the A deck windows are clearly visible and the boat-shapes are immediately above it--right where they should be, as far as I know. What is odd is that the superstructure appears to continue above this level more than it should. Perhaps if the top layer had slid off the ship and spread out on the bottom that would account for the sonar image, but the interview with the expedition leader on the website makes no mention of this. (Incidentally, this image was done in 2003).
The only plausible explanations I can think of for the apparent exaggerated height of the superstructure are ripples in the mud caused by the ship's impact with the bottom, or perhaps overlapping runs as the sonar data was being collected.
Which still leaves the question of what those shapes are, if not lifeboats. As you and Dave say, I agree that it's pretty darned unlikely that the boats would still be there--but those shapes are so regular that it's awfully hard for me to dismiss them . . .
--Jim