General description:
When I open up a pack of Pirates of the Branding Purposes, I don't look at them as cards in a wrapper; I look at them as credit card statements in my mailbox. Knight's Errant is a Capital One bill for $599.06 for a second-hand 4' tall plaid ottoman. (Anyone remember those "What's in *your* wallet?" commercials?)
Uses:
As a gunship, a Galley loses some steam since it can neither pin an enemy ship nor eliminate a mast with a ram. On the open seas, you need as many options as you can get but since Knight's Errant does not sport stats indicative of effective goldrunning, she's better off as a gunship or a support ship and there are far cheaper and more impressive support ships out there which can perform tasks better than she could. The same could be said of other gunships out there but I am trying to be less brutal and more analytical. Yeah, let's see how long that lasts. 
Strategies and game play:
In a 40 point game, you are giving up half of your points just by placing a Captain aboard Knight's Errant. There's not much to be gained by using Cursed vessels as goldrunners, anyway. In higher point games, here's what I'd do: with my ideal crew setup, I would try to pull off what I call a Willy Wonka.
(In the 1971 motion picture Willy Wonka and the Chocolate Factory, Gene Wilder, who portrayed Willy Wonka, hobbled slowly toward the main gates with a cane before finally dropping it and doing backflips to show that he was in fact youthful, flexible and nimble)
I'd reveal my Helmsman and move around at S+S toward a Pirate goldrunner and then, if and when I'm within S+S+S+S of her, flip my Captain and Davy Jones face up, and either charge in for an attack or move the enemy ship closer to my Knight's Errant and then move & shoot.
Combos with other miniatures:
She is the perfect point cost for a Captain, a Helmsman, and OE Davy Jones. This is the most plausible crew setup for making Knight's Errant passable as being competitive. I figure that since the highest stat number on Knight's Errant is its cost, you might as well use it to your advantage. RotF's El Fantasma has some merit as well, giving you a frightening eternal rotten egg of a ship which can be given the lame action twice... Er, I meant same, not lame. Oops, was my Freudian slip showing?
Ways to counteract it:
To be perfectly frank, if you need to specifically prepare for Knight's Errant, and that's assuming that your opponent takes leave of his or her senses and actually plays with one, YOU ARE DOING SOMETHING WRONG. Only in the narrowest of situations could Knight's Errant become a "playa" and even then, you should be outfitted to either deal with it first by derelicting it with your gunship or avoid it altogether with your goldrunner.
Strengths/Pros:
- Her high cost allows the nastier, more expensive Cursed Crew to be assigned to her (i.e. White Crew, Davy Jones).
- +1 to cannon rolls against Pirate ships; arguably the most used nationality in the game.
- The Galley keyword, combined with the Ghost Ship keyword, means that no one ship (carrying a cancellation crew) can cancel both abilities and pin her.
- The Galley "stern turn" gives you optimum post-move action positioning and this ship needs as many advantages as she can get.
- Mixed range cannons.
Weaknesses/Cons:
- Costs more points by itself than most other ships fully crewed.
- Weak rank 4 cannons.
- Too slow for lots of things but particularly too slow to take advantage of its Ghost Ship benefits.
- Exemplary of a movement on Wizkids' part to make ships woefully overpriced and practically immobile.
- Not enough cargo space left over after assigning a Helmsman to her to be effective as a goldrunner.
- An enemy gunship with a headhunter crew or Grape Shot/Exploding Shot equipment aboard would humble her and your fleet in the blink of an eye.
Artwork and aesthetics:
Contrary to its bleak stats, Knight's Errant is very pleasing to the eye. She's every bit the Cursed vessel, from the tattered sails and moldy deck right down to the seaweed-laden oars. Clearly, the Cursed do not believe in housekeeping (shipkeeping?) I'd love to see a comedy skit about a Trading Spaces type TV show where the Cursed and the English trade a ship and the crew aboard it make changes to it. FYI: the definition of the word errant is "straying from the right course or from accepted standards". While this definition sums up my feelings on both this ship and the current Wizkids staff in charge of Pirates, the intended definition is this alternate meaning: "roving, especially in search of adventure: knights errant". Errant is an adjective so it should be called Knights Errant or Errant Knight. With the apostrophe, it works out like "Dog's Hungry" or "Diaper's Full." Hmm. I wonder why would I think of a full diaper when reviewing THIS ship? 
Overall rating:
I rate Knight's Errant a 2 out of 10. She wouldn't be worth 17 points if her ability was "When shooting at Pirate ship, this ship's cannons only miss on a 1". Even within the Cursed, there are ships in the 17 point range and higher that are superior to Knight's Errant. If you've used her in a 40-point game and you manage to win, please email me; I'd love to hear about it. It makes another argument for divine intervention.
Little known fact: Knight's Errant is on La Repulsa's myspace friends list.
That about says it all.