1. 3 telephone poles won't be enough for masts on a boat that big- probably not tall enough either. Even if you do have fore, main, and mizzen masts you're going to need hella big sails, which telephone poles probably can't support. also steering would be a bitch, you'd need multiple rudders unless you tried steering with centerboards a-la
Kon Tiki.
2. I now realize above argument is irrelevant as you seem to have switched to diesel.
3. You don't need a desalinization "plant" onboard, really. Or at least one that would use fuel at all- just make a
Solar still. Of course it would be a bit slower but you could either (a) make a large array of these in one corner of the barge or (b) just scale up one/a chain of
these floating ones and tow the still/stills behind the barge.
4. I've been thinking about something like this myself, and got to thinking that just filling the whole thing with dirt is a waste. You'd want lower levels for storage, machinery, bunks, etc.... and even if you DID fill it up all the way you would have 100+ feet of dirt going straight down. Getting rid of the top decks and leaving the upper bit of the hull as a high wall to protect the dirt section would work, you could leave some of it all the way up at its original height for steering and such. (you'd also want gantries/ladders around the rim of the lowered section)
5. "weld them together"? Yeesh. Have you ever seen one of these in person? You could EASILY support 50+, maybe 100 or more people on one of these.
a bit long-winded, but yeah...