I'm currently listening to the Lord of the Rings on audiobook. In the Council of Elrond they discuss a number of possible options for dealing with the ring, including sending it to Valinor by ship presumably with elves who were departing. They don't seem to discuss the possibility of taking the ring out to the Grey Havens and then along to Gondor by sea. It would then be almost at its end destination. 

It seems to me that this could be simpler than trying to transport it by land. Is there some reason why this would not have been an effective strategy? Maybe a sea voyage would have been less stealthy? Maybe the enemy has some kind of naval superiority?

Given that the ringwraiths were temporarily put out of action at the Ford of Bruinen it seems to me that the passage from Rivendell to the Grey Havens could have been reasonably straightforward around the time the company left for the mountain pass.