Just as characters take damage when they fall more than 10 feet, so too do they take damage when they are hit by falling objects.
Objects that fall upon characters deal damage based on their size and the distance they have fallen. Table: Damage from Falling Objects determines the amount of damage dealt by an object based on its size. Note that this assumes that the object is made of dense, heavy material, such as stone. Objects made of lighter materials might deal as little as half the listed damage, subject to GM discretion. For example, a Huge boulder that hits a character deals 6d6 points of damage, whereas a Huge wooden wagon might deal only 3d6 damage. In addition, if an object falls less than 30 feet, it deals half the listed damage. If an object falls more than 150 feet, it deals double the listed damage. Note that a falling object takes the same amount of damage as it deals.
Dropping an object on a creature requires a ranged touch attack. Such attacks generally have a range increment of 20 feet. If an object falls on a creature (instead of being thrown), that creature can make a DC 15 Reflex save to halve the damage if he is aware of the object. Falling objects that are part of a trap use the trap rules instead of these general guidelines.
So, those are the general rules for falling objects.
I would use the falling object range, since that seems more appropriate but it still leaves a large penalty to hit. Keep in mind that while the base AC of ships is low, it is increased by the proper skill of the driver of the vessel. For a vessel with sails that is profession(sailor). In the Skull and Shackles campaiagn I'm in, my 6th level ranger without any particular focus in it has a +18 between some ship based bonuses and masterwork tools. That raises the AC from 2 to 20.
Also keep in mind each flask has to be dropped individually as a standard action.
Also, they don't do 4d6 falling damage. Alchemist flask aren't even small sized objects. They probably qualify as tiny or diminutive. It should deal either 1d6 or 1d3 falling damage.
Why could you not put 25 in a sack and drop the whole sack.
I mean I know they can but would the best way to work this out be.
You certainly can. You can even make an attack roll using them as an improvised weapon. What you can't do is try to use common sense to avoid the game rules. The game is balanced (as much as it is, different debate) with it taking a standard action to use one flask of alchemist's fire. Something not specifically covered in the rules is being used to create a situation where you are using one free action to use 25 alchemist's fires. Even a cursory look at the situation will say that something isn't right here. There are plenty of cool exploits within the rules, this isn't one of them.
Why could you not put 25 in a sack and drop the whole sack.
I mean I know they can but would the best way to work this out be.
Mostly because the rules aren't balanced around it.
You will never find any RAW ruling on it but I would probably have it work as alchemical siege engine ammunition but maybe without the italicized portion:
Alchemical Fire: This hard, ceramic canister of alchemist's fire can be used as ammunition in catapults and trebuchets. When it hits its target square, it deals 4d6 points of fire damage to each creature and wooden structure within 5 feet of the target space, and each creature must make a DC 20 Reflex saving throw or catch on fire (wooden objects automatically catch on fire). Every creature and wooden object within the area between 5 and 30 feet of the target space must make a DC 20 Reflex saving throw or take half the fire damage, but they do not catch on fire.
On a siege engine mishap, this ammunition explodes before it is launched, dealing its damage to the siege engine and all nearby creatures and wooden objects as if one of the spaces of the siege engine (crew leader's choice) were the target square. This alchemical fire ignores the hardness of wooden objects.
In any event I would not worry too much about it unless you see it being abused. I figure there would be some significant penalties in hitting your square and the cost is like 500 gp with a couple rounds to get it off.
Like I said, not RAW, but I like to reward innovative play and thinking.
You will never find any RAW ruling on it but I would probably have it work as alchemical siege engine ammunition but maybe without the italicized portion:
Alchemical Fire: This hard, ceramic canister of alchemist's fire can be used as ammunition in catapults and trebuchets. When it hits its target square, it deals 4d6 points of fire damage to each creature and wooden structure within 5 feet of the target space, and each creature must make a DC 20 Reflex saving throw or catch on fire (wooden objects automatically catch on fire). Every creature and wooden object within the area between 5 and 30 feet of the target space must make a DC 20 Reflex saving throw or take half the fire damage, but they do not catch on fire.
On a siege engine mishap, this ammunition explodes before it is launched, dealing its damage to the siege engine and all nearby creatures and wooden objects as if one of the spaces of the siege engine (crew leader's choice) were the target square. This alchemical fire ignores the hardness of wooden objects.
In any event I would not worry too much about it unless you see it being abused. I figure there would be some significant penalties in hitting your square and the cost is like 500 gp with a couple rounds to get it off.
Like I said, not RAW, but I like to reward innovative play and thinking.
This actually seems like the best way to run it in terms of damage and effect.
I have 2 solutions, both very similar, but dependant on how the mass of 25 bombs is dropped. the 2 ways I see 25 bombs being dropped that I see is either dropping a bag full of them either closed or open, or using said bag to pour them out so they kind of carpet bomb the ship or at least land in a nice decent sized cluster. My answer as a GM to either scenario involves almost no dice rolls, no initiative, and no combat rounds. The whole scene gets described out in possibly gruesome detail as if it were a cutscene in a video game. Unless you somehow manage or decide that the firebombs immolate the entire crew of said ship, they will quickly begin putting out any fires that happened to start. Best case scenario, you kill off a few important crewmen or have some of the crew still busy putting out fires when you board.
In my opinion the whole thing would better be done not from some exotic flying mount but from the deck of a ship either in pursuit or being pursued by the target ship. The best of both of those options could be accomplished with a fireball or 2 and some very handy archery. Though the archery could very easily be done from the back of said exotic flying mount.
PSY