I'm working on one right at this moment and have never done one before. Here's
what I learnt by experiment:
Basically a background fade to distance fog with a dark blue background. Put a
light parented to your camera with the light set to about 150% but set quite
blue. Turn all shadow mapping and ray shadows off - I found them unnecessary.
Trace reflections only if you get close to metal.
The bottom was made from a fine mesh moved into layout and displaced with a
bitmap image created with VistaPro (but a scanned and smoothed atlas map would
do - just a bit more work). Save transformed and loaded back to modeller and
the mesh subdivided and stretched vertically (undersea valleys tend to be more
exaggerated).
A fractal noise texture map applied to colour - both around sand colour - an
appropriate crumple map applied to the bump map of the surface and away you
go! Experiment with settings depending on the size of your objects and I got a
really good scene within a couple of hours of starting the project.
Stick somethinng into the scene to give it a sense of scale if you can - gives
more realism when you have something to refer to.
Hope that helps.
