I only really do sailing, so I'm going to give my opinion on the cannon/sailing skills too. I'm also going to steal
@tlonge's great idea of having a "rating" system!
Edit: Gonna come back for the sailing skills, this took a while lol
Cannon Skills
Shoot (Rating: 4/5)
This is a much more important skill than many pirates realize. With the cannonballs that fire in volleys of three I believe this skill has a much greater overall damage increase than any of the passives. When watching the "reload bar" while firing a volley, without the Shoot skill you will see the bar fill to about 1/3rd each time, whereas with Shoot it'll only fill to about 1/8th. That's over 50% less time "wasting reload" between shots (3/3rds = 8/8ths vs 3/8ths).
However, this skill has zero benefit to single-fire shots such as explosive and thunderbolt. With certain ammo builds (depending on your ship hulls), it might be preferable to drop this skill over one of the passives.
Rapid Reload (Rating: 4/5)
Rapid Reload increases your overall damage more than Barrage, at the cost of spending ammo faster and not increasing your ship broadside damage. 5 full points into Rapid Reload is 30% faster reload, which means approximately 30% more volleys in the same amount of time, which means approximately 30% more damage. This skill increases the damage output for all ammo types (including single-volley ammo), reduces the punishment of missed shots, and shaves off a
lot of time reloading for explosives.
Barrage (Rating: 5/5)
This skill is necessary. Five points into Barrage is a full 25% damage increase for all ammo types (including broadsides). This is the same as one skill point into any particular ammo. Not much more can be said about it.
Shrapnel (Rating: 0/5)
This is an absolutely useless skill. It increases the duration of wounding effects of cannonballs and grenades.
This does not increase the burn time for Firebrand. This is a remnant from the era when you could see (and shoot) the crew on enemy ships. You can get this skill for grenades, but just know that for cannons it is entirely non-functional.
Round Shot (Rating: 4/5, 1/5 broadside)
Round shot is an almost essential skill. If you sail at all, you should always have this skill maxed out (even for ships with special broadsides) as it increases broadside damage significantly. Additionally, with full Shoot, Rapid Reload and Barrage round shot has much more damage output than a lot of people expect. Unlimited ammo is always a good benefit too, and without functional cannon rams this is the only way to get it.
This is the regular ammo for broadsides.
Chain Shot (Rating: 1/5, 0/5 broadside)
I am unsure what the damage multiples of chain shot are, but they do significantly higher damage to sails at the cost of much lower damage to hull. An uncommon ammo type, Chain Shot actually does have its uses. Stripping the sails off ships can be very useful in certain situations, such as a small crew helping the captain get sailing rep (crew takes out sails, leaves the crippled hunk of wood to the captain) or focusing on hunters for (strip a warship of all its sails and leave it dragging behind you). However, generally speaking, Chain Shot is a waste of skill points.
As broadsides the Chain Shot is only seen on NPC ships. Due to its immensely weak hull damage, and since broadsides aim for the hull, this is by far the weakest broadside in the game.
Grape Shot (Rating: 1/5???, N/A broadside)
I can't actually say much about grape shot, as I have literally never used it since they changed how it functions. Originally it was used to kill the crew members on board ships, but as I said about Shrapnel that is no longer a thing. Apparently it was changed to be a more SvS relevant ammo, but I hear the "repair slowing" effect it claims to have does not currently work.
For broadsides, no ship in the game fires Grape Shot.
Firebrand (Rating: 3/5 cannon, 2/5 broadside)
Firebrand deals
1.25x the damage of Round Shot. Other than that, it acts identical (though it looks cool!), as the burn effect is non-functional at this time. Back in POTCO's day the base damage of Firebrand was actually
lower than round shot. Since the burning effect did not stack, a volley of firebrand was weaker than round shot (side note: this made firestorm the weakest broadside in the game, with fortune hunter a close second-to-last, with regular broadsides at third-to-last). However, in TLOPO, firebrand simply does more base damage than round shot.
As broadsides, firebrand makes the weakest player-obtainable special broadsides at a measly
115% average damage for Firestorm and
111.25% average damage for Fortune Hunter. It's a heck of a commitment spending 5 skill points for such a meager damage increase.
Thunderbolt (Rating: 4/5 cannon, 4/5 broadside)
Thunderbolt is one of the most popular ammo types. A single thunderbolt does
3x the damage of Round Shot, but only fires in volleys of one. This means a thunderbolt volley and a round shot volley deal the same amount of damage. However the thunderbolt wins as without multiple shots per volley you can fire more volleys in the same amount of time. Though the difference in overall damage against Round Shot with max Shoot level is minimal, thunderbolt does not require Shoot for max potency. More importantly, however, thunderbolt is long range and high velocity, making it the easiest shot in the game to aim.
As broadsides, thunderbolt makes the second strongest but most reliable damage output. At an impressive
190% average damage, a Storm Chaser hull upgrade is well worth it if you are looking for firepower. Additionally, if your broadsides do not lock on, their light weight and high velocity make your "spray and pray" broadsides travel further. This is highly useful for tagging hunters/warships speeding by as they chase down prey across the world, ensuring you get some free goodies!
Explosive (Rating: 3/5 cannon, 5/5 broadside)
Explosive is an interesting cannonball. With no unlimited-ammo rams, a meager 12 ammo capacity with the biggest barrel, and an immense reload time, you won't be firing these things often. However, they do a whopping
12x Round Shot damage. A well levelled pirate can sink many ships with a single explosive. Though powerful, and useful in many situations (most notably SvS), it often loses out to Thunderbolt and Fury for the skill points demand, and many players prefer not to invest in this cannonball.
As broadsides, Copperhead boasts the highest average damage output at a whopping
265% average damage. However, the Copperhead's damage is unreliable due to its low (15%) chance of explosives. There is a good chance to fire zero explosives from a broadside, no matter what ship you use (War Frigate 20%, War Brig/Galleon 15%, War Sloop 33%). Inversely, it is possible to fire more than one explosive, resulting in an incredible damage boost (320% for a War Frigate/283% for a War Brig at two explosives).
Fury (Rating: 5/5 cannon, 3/5 broadside)
At
2x the damage of Round Shot, but acting identical to it (other than looking flash), Fury has the highest raw damage output of any cannon ammo out there -
when used in volleys. The only downside Fury has against Round Shot is the limited ammo!
As broadsides, Skull and Bones claims
150% average damage. This number is much lower than people tend to expect. Fury is known as the highest damage output for cannon ammo, but it's typically fired in volleys of three. As broadsides, fury is fairly lackluster compared to thunderbolts and explosives. A major advantage to fury broadsides however is you are not tying up skill points in other cannon ammo.
This has taken me longer than I expected to post, so I might make a second post for sailing skills. If you're interested in how I got all these numbers, take a look at the discussion thread link in my signature.
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Arrr ~