In situations like this?

The trains must run.

That is always the simplest way to calm down a train. You point it in a direction, build up its steam, and let it burn itself out. Trains are creatures of motion, of energy pent-up and tamed and forced into pistons. If you're not there inside them to calm them down, if you're not willing to sit with them and calm them down and help them understand that no, running heedlessly ahead isn't the best plan, if you don't have an engineer listening to their needs and a knight to clear the way, the train will run regardless.

Of course, that's the simplest way, and ignores that running more than about ten feet in any direction right now has a rather precipitous drop-off.

But that's actually the key right now. Sasha is stressed, wants to move, wants to run, wants to be free, and she's pinned down holding the raft together and being forced to sit still with a belly full of steam. If she's not given a direction, she'll pick her own.

So, that means he's got to pick one for her. Give her a direction.

And that means that part of the raft has to go. She's pinning the raft together, but if... Hmm. The logistics of this one are a bit hard, because cutting any part of the raft off means that the train's off-center, but he should be able to jury rig Sasha a bit closer to the edge, let her legs dangle a bit in the water, and Sir Hatt as his witness, he's going to teach a train to dog-paddle.