Thanks for the encouraging comments guys.
I didn't check smallg's script out but I saw the videos so is likely done in the same way. There is one script that runs the ship for the speed, rotation, height, animations, collision with terrain etc. And another script that tracks the ship and places the player on it, intercepts the WASD & shift keys to add incremental aggregated relative position movements to the origin of the ship. The tricky parts were not for the translation movement of the ship/platform, but for the rotation - keeping the player in the correct spot when the ship rotates and moves forward at the same time. The other tricky bit is tracking where the boundary of the ship is (as there is no collision active) - straight forward if you use circular distance from a central point, but a bit more math required to find the edge points of a rectangle with a bow. Also had to keep track of where the player was on ship to adjust height up the stairs and so can go through the door of the ship to its inside (not shown on video), which is a transport to a hidden interior ship model.
The FXAA addition to the shader is probably not obvious in the video. I hadn't really noticed the jagged edges too much before working on this aspect, but I notice them all the time now with FXAA off. Still fine tuning this.
@lordjulian & @Mariokiki - I'm sure there will be a much easier way to do this kind of thing in the future with GG but as I'm on a mission to create viable airship gameplay by Q1 2017 (amongst other things) I'm putting the hours in now to see how far I can get - don't think its a viable store release given the amount of tuning needed per model.
@3com - It's not shallow water, there's a 'swim' script I released on these forums somewhere (I'll see if I can find the link, if not I'll attach it here again) - for first person only though.
@Lee - I'd be very grateful for anything you could add that would help (and sounds like others would find this useful too). I did kind of hope that the juddering would be passed off as engine vibration during the game as you mentioned, but there again people might just think it's a bit poor (I was being optimistic with that hope perhaps).
Cheers.