Re: large underwater object found. unkown origin
We probably won't hear about it again because it'll turn out to be nothing. I use side scan a fair bit, and you'd be surprised at how deceptive the images can be. To me, this looks a lot like a rock, and not even one shaped the way the image looks.
The horizontal lines in the display in those pics show that vertical is the time scale, IE it's a "waterfall" type display where the boat is traveling in the "vertical" direction and new lines are added at the top while the display scrolls down. Each line of pixels on the screen is probably about 1 second or so of recording time, so the display shows several minutes bottom to top. The slightly lighter horizontal lines running through it show that every 20-30 seconds something happened to make the signal a bit messier... could be anything from noise from the boat to the towfish being jerked a couple feet upward by wave swell. You can see in the image just after the "object" that the fish got tossed around quite a bit... that's all the lines compacted together.
(The lines I'm talking about are the gray/black ones, not the blue range lines)
Here's the thing... as the fish travels and records a line at a time, the picture we see isn't a "snapshot" but rather a composite of lines. If the fish doesn't travel (like it happens to sink or rise for some reason) the amount the boat "thinks" it did then it can record essentially the same line twice... and presto, that part of the object looks twice as wide.
Looking at the object in the image, I see many features that are repeated looking like "ridges" that are parallel to the direction the sonar traveled, kind of like pulling a comb through mud. If you take a bump or a hole on a rock and "smear" it along because your sonar recorded each inch twice, it turns into ridges like these.
Putting it another way, it's like a paper jam in your printer, where the paper either slips and doesn't move, or moves too far... you end up with overprints and gaps, because the only time you get a perfect image is when the paper moves just right... hard to do at sea, when towing your "print head" a mile down. It easy to see in a color printed image where things went wrong... much harder with a black and white image of an unknown object.
Taking a wild guess I'd say the object is only about half as "tall" as it looks proportionally, which would make it a largish oblong rock of no other interest whatsoever.
Just a quick edit: I'd say the thing actually looks much more like this than the above pic. OMG! It's a big stone statue of a bear!
Also, looking at the sub the guy has there, it's pretty obvious he's been planning for a while (the subs are custom built, and much more expensive than an "exploration" sub) to take paying customers into the ocean. Which is going to attract more customers for him, a sonar scan of a pile of rubble that used to be a ship, or an "unknown object" that *might* be a UFO?
Erik
. Obi-Wan Kenobi please save us. 
