Heh... having served aboard submarines, I can tell you that you simply don't ever need to clean the hull.  Just take 'er out into some deep water and put some serious turns on the screw.  If there's anything living still hanging onto the hull after about 15 minutes of that, you should probably back away from it very slowly. 😀

As for building pressure containers and turning them into data centers and sending them to the bottom of littoral waters, it all seems to be a bit stupid.  If you look at the number of sacrificial anodes they had to attach to the hull to keep the hull from disintegrating, you'll understand on of the many reasons why.  Then there's the cost of cable, etc.  I'll also tell you that 117 feet doesn't make these things immune from wave action during a good storm, never mind any special currents that happen when a tidal surge returns to the sea.

And, lordy, I hope this doesn't actually catch on.  Imagine all the cables on, near, or under the seashore if it does. 

I do think it's an interesting and clever endeavor but I think it would be much less expensive to rent some garage space from different companies downtown.  You could probably save several years of rent on the cable cost reductions alone.