NVGs over water are a bit of a problem especially when out in zero light. Unfortunately, you are left with the IFR / NVG blend to keep things safe. Many times over water you may be left with a single target point of reference such as a single distant vessel which is essentially a single point of light on the goggs. This can create gyrosomatic illusions leading to the leans. I know that much of the time the RN will rely on IFR procedures for transit and winching ops.
In fact I've experienced problems in daytime VFR SAR scenarios with reasonable visibility, solid overcast, calm water and no horizon, and little IFR experience to back me up. The only thing that prevented me losing references was back to basics, trust the instruments and find a land reference as soon as possible. These scenarios are very similar to the NVG op, but you have fewer cues and a bigger head scan to complete with the NVGs. Nothing else for it! Get the IFR training and if you can, engage and manage your autopilot at the first possible opportunity.
It's really important to realise that if there is no light there, and you cannot provide your own illumination, you may as well be IFR, for all of the use the NVGs are over featureless terrain or water. Any limitations that the army provides are primarily designed for desert operations, good meteorological visibility and low humidity with few ground references and a high liklihood of recirculation. They are not designed for over water ops.
You don't say what you do with the NVGs over water... or is it so cool you can't talk about it?