Maeroda,
I have no experience in overwater flying with 139 and his EGPWS but I think it would be as great as in mountains.
I am amazed that you can make such a statement - on what logic do you base this conclusion?
As has been pointed out in another post recently, the obstacle environment offshore is only partially mapped - that makes the 'E' portion of the EGPWS somewhat suspect. The 'GPWS' modes are based upon the six classic fixed wing modes (yes, modified for helicopters, but still based upon the climb, descent and landing modes of the aeroplane).
For onshore work, the enhanced mode of the EGPWS has great potential; for offshore work, we await the real-time obstacle detection that Honeywell have promised us. For all helicopter flying, we welcome the increases in the size of the market because that might lead to additional work to provide realistic classic modes.
Jim