When rolling under your stat, a critical success is if you hit your stat exactly. This is purely a cosmetic change but I don't like the feeling of "Yay, I rolled a 1!"
When you have a bunch of allies and enemies fighting each other but it's not big enough to abstract as a battle - maybe it's a boarding action on a ship or an encounter between two large companies. And nobody wants to deal with all these nameless mooks instead of the cool PCs. And let's assume that because they're mooks they have no special abilities and are functionally equal to each other (e.g. all 1HD fighters).
Have some of the enemy mooks engage the PCs, however many seems reasonable. Pair up the rest of the mooks against their opposing numbers. Each round, the players roll a D6 for each 'pair'. On a 1, the ally dies; on a 6, the enemy dies. If one side is strictly twice as superior (e.g. two onto one, or a 2HD orc onto a 1HD goblin) then double that side's chances of victory. As soon as the PCs engage with the mooks, they start running on the regular combat rules.
This rule gives the mooks a fairly low chance of harming each other, and is based on the idea that in swashbuckling combat, the mooks should fight "in the background" while the PCs are the focus. Most of the mooks will keep hacking away ineffectively at each other until the PCs (or powerful NPCs) shift the tide of battle.
LOST AT SEA
Being lost at sea means you are lost with no ability to navigate and no means of propulsion, so maybe you got shipwrecked, marooned on a raft, fell off, etc. You have nothing you can do except sit around and wait. Make a save vs. death, fortitude save or luck check. If you fail, you die of thirst. What? You shouldn't have gotten lost at sea in the first place, dumbass. If you pass, you are washed up on a random island or fished out by a passing ship.