Large group combats

Hmm, need to give some thought to what to do for ship-board actions in the Maritime Campaign. I'd rather not spend time rolling 20+ attack rolls a round for the NPC crew members, and equal numbers for their adversaries.

The War Machine is a bit much, and I'd rather not dig into Chainmail right now (I've only got it on pdf, and only have skimmed the rules).

I'm thinking I need a system where I make one die roll per troop type, then adjust damage depending on how well or poorly that roll went. Dice of damage would be then be divided between the enemy forces, one die to one opponent.

But do I want a flat roll, like a normal d20 hit roll, or a curved distribution like a 2d6 roll? Or should I dispense with attack rolls and just assume a number proportionate to the chance to hit defender AC are hit each round?