If we're going to chase them we need to watch out if they departed down or upriver.
If it's downriver, they could join with possible reinforcements there, and we won't be able to outrun them. Chasing upriver's fine.
They departed downriver. By now, with them rowing upriver during the morning and getting into a scrum, it's Midday at the very least. It's a day and a half of travelling by boat to the Count's town, which may potentially be an enemy camp. They will disembark at least once before then. With our part of the river being only 100m wide, that's well in bowshot, and we probably peppered them good even though they escaped. They will camp to tend their wounded and rest.
I don't know why the raiders would have more ships following a raiding fleet that is already intent on picking clean the river lands. That's like going sloppy seconds on a tavern wench. They've had little resistance in sacking that town downstream, and probably don't have a high opinion of what they've been facing so far. It's worth the risk to assume that they will set camp at least one night far from support.
Assuming late arrivals don't change the vote, I'll sharpen up the battle plan a little before Mal can unstick himself from his gainful distractions.
Rough PlanReplacements: First, we lost a few halberdiers from our retinue, so we get the veterans observing the levy block to pick which men were most bold in the action over there. They are our retinue replacements now, and potentially in the future if they like. Fill a company of 35 halberdiers.
Fire Arrows: Make sure, in the time that we're delaying our chase, to prepare plenty of wool strips to oil up and set aflame. We're a wool town, so should be easy. Giving the raiders some burning ships to worry about is pretty crucial, so if we roll badly, fire another volley until its a done deal.
Lanterns: The mode of setting these on fire is hooded lanterns. We shouldn't risk open flame in a surprise night assault, or even on a wooden craft at all, for that matter.
Approach: Let us go light on the oars, and no sails to be observed from shore. We have plenty of time to catch up at night. At night, keep to the midstream, so as not to beach on shallows. A few men knowledgeable of this river should be piloting. Immediately upon seeing the campfires, disembark the halberdiers, and the archers drift down stream with oars only guiding them as needed to remain in the middle course of the river. Anchor. Launch fire arrows till it sticks and then peppers the raiders illuminated in the blaze.
Attack: We rush in and blow a horn to signal the archers to cease their firing, or potentially concentrate on a undamaged ship that has managed to launch. The raiders are bewildered, panicked about their ships, and not expecting landward attackers. Hopefully, this is mere mop-up.