Backwalk and fall into the water then climb onto the platform. Hold L, sidehop, then immediately backflip. You should have landed on the wooden boat without triggering the text. Climb to the bow of the boat, then roll/jump to grab the rock face.
After the initial FF1 cutscene has ended, turn left so you are facing the rocks. You want to stand near the edge of the water and angle yourself just slightly to the left of the wall. If you are angled correctly you will jump right past the wall and grab the very edge of the rock face when you roll and jump off of the ledge.
Note: Later in the game, you will encounter a dead end if you have performed this trick by any method since you will lose your sword next time you enter the pirate ship. Therefore, this trick should only be used in an individual level speedrun of Forsaken Fortress or a smaller race to Din's Pearl as a timesaver.
Simply roll at an angle off of the walkway to the window and perform a sidehop directly after landing to prevent a bump into the wall. From here, you can navigate your way to the searchlight. Also, as a quick way to dispose of the bokoblin, you can lure him towards the ledge and use a quickspin to knock him off of it.
After you have climbed the ladder to the first searchlight, bait the bokoblin into attacking you until you health is reduced to 1/4th heart before killing it. With a deku stick in hand, move over to the ledge and stand on the second black splotch from the right. Now your situation will determine your angle. If you are preforming this trick as part of a FF1 IL, you will want to use C-up to align just right of the big door by the hero's sword. If you wish to grab the hero's sword, you will have to align with the heart on the right that is along the sidle ledge.
Note: While you're hovering, you can still be detected by the two remaining searchlights. Although they cannot catch you mid-hover, they can if you land and heal. For the runner who still wishes to collect the hero's sword, this means constantly readjusting the height of your hover as to avoid being caught by the searchlights. However, the timing for an IL of the dungeon ends upon touching the loading zone behind the big door. For this reason, this trick is most likely to be used only in the IL scenario.
Once you have selected your angle, exit out of C-up and wait for the camera to pan out. Jump off of the ledge and at some point once you have cleared the walkway directly below you and Link stops moving forward in his jump do a jumpslash. If you did the jumpslash at the right time Link will either:
In either case, you want to mash B in order to start the hover. This is because, in situation 1, the first slash you take will pull you off of the ledge allowing you to hover OR in situation 2, the recoil from the stick hitting the boat will push you off the ledge allowing you to start the hover. From there, just hover to where you desire.
It is important to note that it is completely unnecessary to disable the second and third searchlights in the process of getting to the hero's sword. These are referred to as the "second" and "third" searchlights based on the assumption that you used the above trick to disable the "first" searchlight.
Unless you are right next to them, you will not immediately be caught simply by being in the sight of a moblin. It is possible in most cases to easily escape the moblin's field of vision with good and well-timed rolls to get around corners and over hills quickly.
Instead of simply holding the control stick in the direction you wish to sidle, push the control stick lightly and rapidly. This will allow you to cross the distance a bit faster.
It is possible to get inside Forsaken Fortress without needing to blow up the front door and get in on the second visit. Instead, you can swim to the standable spot on the left side of the fortress and item Slide through the corner at that location. From here you can swim underneath the Phantom Ganon trigger to start the battle and be teleported to it, out of the water. This not only skips blowing up the wall, but also the cutscene with the KoRL that would normally play as you enter. If you clip through the wall and go way past Forsaken Fortress, you were likely aiming too far left, if you only go past it a little bit you were likely aiming too far right.
After you equipped the Skull Hammer, walk up the first two stairs. Stand on the wall facing the ladder on the other side of the area and use your leaf to glide over and grab it.
After obtaining the skull hammer, there is a series of Item Slides that can be used to quickly get to the top of Forsaken Fortress. The first of these is used to clip through the skull hammer pegs blocking the initial stairs. This slide will only work if you're in third person while sliding so be sure to take out a bomb or the skull hammer before going through the pegs and up the stairs. The second slide is simply up the short ramp to get to the location of the item slide that crosses the entirety of Forsaken Fortress. The giant item slide across Forsaken Fortress is somewhat precise and home buffering ZL, B, and Forward on the analog stick is recommended. The next few item slides proceed to climb the next set of stairs and the winding path up to the top door of Forsaken Fortress.
After coming back to Forsaken Fortress from Ganon's Tower, it is fastest to clip out of the island and superswim away from it. To do this you will want to Item Slide (as shown in the video below) to the irregular rock formation on the western side of the island. From here you can clip to the outside with an Item Slide clip where you begin an Item Slide and then hold Up after about a second. If you are not clipping through, or you are clipping through too far, try adjusting your angle to be either more to the right or more to the left than what is seen in the video (this can help if your ESS position for Item Sliding is not perfectly straight).