Hi steve.
With a missing "up and down"-effect I mean there is no physical difference of the subs' movement depending the wave heights. If big waves are coming, they just roll over the bridge. If you choose twice big waves the bridge is just deeper under the surface, but the sub itself isnt affected by bigger waves...its just the bridge which is more or less under the surface. Just have a look on the horizon and you see what I mean
Its just the same physic, same motion, no matter which wave heights you have choosen
Hope that explained it