Wow! I would not have been surprised if you had said it weighed twice that.
Just to make sure we're on the same page, we are talking about about a boat that has all the batteries, motors, electronics, etc that's ready to go in the water. Right?
Up to now my only reference has been Johann Sauer's Walter XVIII which he said weighed about 70 pounds or more. Of course, it was entirely a dry hull type. Maybe that's the difference.
I was going to pass on the OTW S sub because of weight. Now, I'm not so sure.