HOW TO... MASTER NAVAL COMBAT
The positioning of your ship can be crucial to success during naval battles and where possible you should try and manoeuvre yourself so all enemy ships are to one side, making it easier to keep track of their threat and concentrate your firepower. Avoid approaching from the side of hostile ships as this leaves you open to their cannon fire, instead sail towards them at an angle then turn sideways when you are in shooting range.
Using Full Sail will allow you to travel much faster but you won't be able to turn as quickly, whereas Half Sail give you improved manoeuvrability at the cost of speed. Keep an eye on the wind direction indicator on the mini-map as you will travel much more quickly with the wind behind you, marked by the indicator showing green. If a rogue wind appears it can blow you considerably off course, so lower to Half Sail or No Sail until it passes to minimise the impact.
When firing the cannon holding down R1/RT will focus your aim, narrowing the target area and increasing the accuracy of the shot over longer range. When enemies are close this level of focus is not required, so simply press and release the button to get your shot off quickly. If you do find yourself in the middle of a group of enemies it's worth noting the cannon on each side of the ship fire independently, so you can shoot in both direction without waiting to reload.
The swivel gun has a much wider scope for aiming and is great for taking down small ships, but don't bother using it against large vessels unless you've already exposed a weak point as it won't have any effect. Hold down L1/LT to aim the swivel gun then release as the reticule turns red to land your shot, be quick though as you often only a short window of opportunity to hit your mark.
Pay close attention to the information shouted out by your crew members, as this can often provide invaluable advice on setting your course or warn of imminent danger. Be sure to brace by hitting Square/X when they announce incoming fire to minimise any damage taken.
By interacting with the book next to Harbourmasters you can purchase upgrades for your ship, and although these are expensive they will make subsequent naval encounters much easier. Initially you should invest in the Improved Rudder for greater manoeuvrability, plus the Extra Cannons and Piercing Rounds to increase the damage you can inflict on enemy craft.
HOW TO... ACHIEVE 100% COMPLETION
You can check on your progress towards 100% completion at any point by accessing the DNA Tracker in the pause menu. Once you zoom in to a particular segment, you can then scroll up and down to check all the individual challenges required for it. The DNA Tracker is a handy reference tool as it shows all the side missions, activities and collectibles required for 100%.
When playing through the main story missions you should always be aware of the optional objectives, and try to complete as many of these as possible along the way. If you fail an optional objective you can always reload the last checkpoint and try again, which will save replaying the whole mission later.
Unless the optional objectives state otherwise, they don't all have to be completed in the same playthrough of a mission, so if you find it easier you can achieve them individually and they will stack. However, you do have to complete the entire mission and wait until you return to the menu for any additional progress to be saved.
You should initiate as many side missions as you can, as these stay active and by keeping an eye on your mini-map you can often clear multiple objectives in the same area, saving travelling time later on. Grab any collectibles you see as you go along, but don't focus too heavily on completing these sets until you reach the end of the main story as some items are not available until then. Maps can also be purchased from General Stores to display the locations of feathers, Almanac pages and Trinkets.