Word for a very nimble boat?

There is no single answer to this question but if we look for a small, nimble and long-established boat, the coracle is pre-eminent on all three counts:

Coracle = a small, round boat that is made by stretching animal skin over a wooden frame

Cambridge

The definition does not cover all aspects of this ancient vessel. Here is an extract from a long and relevant article:

The coracle is one of the simplest and strangest-looking boats ever designed for use on our rivers. It has been used by hunter gatherers for many centuries and is thought to date back to pre-Roman times. The coracle is also one of the most unusual boats to paddle along Britain’s inland waterways. Down the centuries it has been used for everything from fishing and transport to postal deliveries and poaching.

BBC

Also see

Coracle Society

And here is one in use:

Canal and River Trust

Coracles are certainly nimble. But, as you're talking about "a switch from a very static environment to a very dynamic one," perhaps

Like steering a RIB.

RIBs may be better-known in the UK than the US though. But then, so are coracles!

Like steering a rigid inflatable maybe.

Since the OP has clarified that any aquatic craft will be acceptable, my suggestion is

Instead of trying to turn the Titanic, it'll be like steering a Jet Ski.

A Jet Ski is a nimble craft known for being able to change direction very rapidly.

While the term Jet Ski is a brand name owned by Kawasaki, it's used as a generic term for these kinds of personal water craft.