The really hard part is the combination of the very short range of light transmission underwater and the very large size of the oceans. How many centuries are you willing to spend on the project?
I think this is one of the systems used during the MH370 search, apparently it can scan 192km² per day.
There are 161,000,000 km² of ocean, so you'd need at least a million days or 3,000 years to scan the whole thing, give or take.
I would think they would need a version that doesn't need the ship nearby to scale - but would still guess this is something that will be accomplished on the order of 30 years from now.
Sorry if you aren't the best choice, but I had to ask someone in the thread.
Why? I mean why all the ocean?
If the purpose is to find archeological sites, most will be on the continental platform.