Once you have completed a shipwreck map, proceed to the sea indicated on the map. You will need the "Salvage" skill or an item with the "Salvage" effect.
If you are on the exact sea, move your cursor back and forth across the map in your journal. It may reveal an "X" pointing out the possible place where the ship sank, but this is only a probability and the ship may be on a different location.When raising a wreck, your ship may take damage and your crew thrown overboard.