As far as I know, the developers handle natural game-elements in a natural way. For example the clouds. They're 3D and every part of the cloud calculates for itself how to let light through etc. Vey beautiful and effective!
Now the same thing could be done with viewing distance and an advantage for the crows nest. What if the sea, instead of a flat plane, could be a tiny slice of a 6371km radius sphere? Like cutting a slice of an egg; the surface will be curved.
Now you can see less far on deck than when you're up in the crows nest and everything would be more natural. For example, you could see just the top of a sail on the horizon. Add in some atmospheric 'fog' and you can make good use of the spyglass.