What is the state of sea travel in Faerun?
How reliable is sea travel? Will ships wander off course?
How long does sea travel take? Can people be stranded at sea for months?
Can nations in Faerun effectively police their waters? Will ships in local waters be attacked by pirates or magical creatures?
I guess PCs are almost narratively guaranteed to have bad events occur but what about for typical travelers?
My personal knowledge of the setting is this.
In real life the marine chronometer and the sextant really only date to the 1700s and so I'm not sure that they fit properly into Faerun's state of medieval stasis unless these were restricted to particular high tech groups.
Mostly only higher level D&D spells such as Commune seem to be usable for marine navigation. However, D&D spells are focused around dungeon crawls and not necessarily what would be most practical in real life. Utility spells for sea travel are a blank area that GMs could fill in as they choose.
Furthermore there are a great number of pirates and hostile sea creatures that live in the oceans and actively attack ship travelers (although a lot just seem to demand tribute.)
So I think sea travel should actually be quite scary and unreliable in Faerun.
Best Answer
Traveling by sea might have been really dangerous - not more than traveling by land in certain areas - mostly because of living hazards.
Crews that do not pay homage and make sacrifices to Umberlee, or that are not protected by Valkur or Shaundakul, might be ambushed by creatures of the deep, and the same goes for enemies of the Society of the Kraken.
Some regions are also controlled by the typical D&D sea civilizations, including kuo-toa and sahuagins, and pirates are surely a thing, but land travel has orcs, goblins, kobolds, the more rural giants (ogres, trolls and hill giants) and bandits of all sorts. The only reason why traveling by sea might be more dengerous is that the ships are mostly used by land-dwellers and their guards are not really good at patrolling the sea as they do with the high roads. While this is also true for the real world, the real world balances that by having the main source of piracy among land-dwellers as well. D&D has underwater races that are way more accustomed to the environment. Basically, ships have the same protection as conestoga caravans crossing the wild west. There are hostile Indians, there are pacific Indians who won't go out of their business to protect them and there is the rare fort here and there (guard ships): I'd expect ships to travel in groups and with armed escort. Especially convoys who want to travel to the hostile, unknown coasts of Matzica to look for the riches Amn is importing already.
Coastal travel is way safer because there are civilized cities on the coast and partolling the coast would be expected.
Ships from large merchantile companies are expected to board some kind of priest of mage that who cast control weather or generate winds on command, making weather a minor inconvenience.
The spells and equipment published in It's wet outs- uh, I mean Stormwrack make the whole seafaring thing safer. Sextants do exista and they "only" cost 250 gp (and even without one, using stars to find the north is just a survival check). Control currents, favorable wind and the everfull sails make it hard to be hampered by a calm, while detect ships and flowsight protect from being approached by pirates and sea creatures.
Casting locate city from Races of Destiny means being able to find nearby ports. As always, casters are really great at helping even outside of combat.
Of course, adventurers more easily sail towards the danger than not, but I'm pretty sure crews might hire adventurers to protect their charge. How many adventurers are ok with this kind of life depends, I guess, on how much they get paid.