And Radio-thermal generators have been in use for just as long, but the only economy to use them as a basis of power generation fell apart (Russia). Simply having been arround a while and past the development stage does not make something a foundation for an industry or program, any more than fuel cells and solar power are teh foundation of our current power grid. "we can do it" or even "we've been able to do it for a while" is not the same as "everyone is already doing it." Ocean going trips may not have been the norm, though realistically they were not hugging the coasts either- they stayed within sight of land- roughly 5 miles to a horizon, not within easy swimming distance, and were making long voyages which included bringing foor for overnight sailing (as opposed to say the ancient greeks who had to land every night)