There is no need for physical proximity, at least not in the slave kind as is offered here, the only reason I want to physically move to the US is the ability to get off my computer at any time and meet cool people for coffee or whatever.
Being stuck on a ship solves that problem no better than being on a different continent.
This would be my fear, one only needs to look to the middle east in which Asian labor is imported and then is basically indentured once they get there, even the US bases take advantage of the captive "contractors". The fact that ages are probably a big factor with these endeavor the propensity for these to truly become slave ships beyond the reach of most laws is concerning to say the least.
Being from the UK you get 90 days in the US, then you need to do a visa run out of the country and can then come back. I think as long as you are being paid by an non US business immigration don't mind.
Perhaps instead of a trip to Mexico or Canada a night on the boat would suffice?
Imagine you're stuck in close quarters, day-in and day-out on a ship with 1,000 other entrepreneurial types. Why would you want to go to the mainland to network in coffee shops?
I understand you might want to get off the ship to hang out with non-tech folks, but you can do that right now in any country. Blueseed looks to me like a perpetual tech conference. The sheer physical density of creative talent is far beyond anything you could ever get on land.
If it really were 1/2 hour trip it would be one thing, but there's no guarantees on that at all.
See http://blueseed.co/faq.html#visa for more details.