bloAdjFriendlyFort = -4 // brown water blockade, bonus given by adjacent fort
bloAdjEnemyFort = 4 // same, for an enemy fort (malus)
bloMinSUToBlockade = 8 // Nb of SoL elements needed or pts given by a fort to blockade a zone
bloValueBySU_LinkCut = 23 // Perc chance for each combat ship (cumulative) that a transition link over water is cut between 2 land regions.
bloMaxPerc_LinkCut = 90 // max chance to have the link cut.
bloMinSUForLinkCut = 4 // Min nb of elements in offensive posture in a water region to cut the transition link between 2 adjacents land regions
bmbHitCoeffLand = 20 // coefficient (in hundredth)to land efficiency for bombard
bmbHitCoeffNav = 5 // coefficient (in hundredth)to ship efficiency for bombard
bmbMaxHitsDoneByLand = 40 // How many hit points can be done by Land units against a fleet
bmbMaxHitsDoneByNav = 40 // the reverse
bmbMinEntrenchLevel = 3 // Minimum level to reach by an artillery so that it can bombards or interdict ships& water supply
bmbRange = 4 // Minimum range a gun should have to bombard (both land art & ships)
bmbAllowSupportAnyCoastal = 1 // if true, bombardment can be done against an enemy not in a structure, if we have a stack in the region
bmbAllowFreeFireAnyCoastal = 0 // if true, bombardment can be done against an enemy not in a structure, even if we don't have a stack in the region
Just to add a bit of clarification. you need 8 combat ships to blockade (so transports don't count) If the enemy has forts with artillery, the number goes to 12. So if you organize 12 ship blockading forces, you will get it done. (And they made it easy with blockade squadrons...they have 8 ships as default.)
A couple other points, the fort effect in cutting supply/blockade malus (and in my experience, Union blockade of ports via forts) is an artillery effect. You must have artillery in the fort for bombard/blockade impact. Note the hit point cap: The most damage a stack of ships or a stack of artillery can do to each other is 40 hits. If you break up your arty in a fort into multiple stacks, you can hit multiple times. (3 guns in 1 stack 40 hits, 3 guns in 3 stacks 120 hits).
In practical experience, shore guns eat light ships for lunch, but Ironclads turn the tables. A stack of 4-5 Ironclads can easily deal out 40 hits and receive none. Considering that even heavy naval guns only have 12 hit points, Ironclads can wipe out a fort's guns, at which point it is like the fort isn't even there.