Okay, next revison I'll take that into account
this is it for now
Among other things, this is almost the exact opposite of a Q-ship.
First of all, by definition a Q-Ship has hidden armaments to catch a vessel by surprise. What you have is...either someone who really wants to beat back endless sacrificial waves of pirates or a really half-assed warship.
Secondly, an effective Q-Ship would almost have to be a somewhat newer vessel for the exact reason people mentioned - you want good, healthy engines because you need to be fast. And as others have pointed out, that's not the only thing - you need a ship built for speed in the first place. The Kreigsmarine raiders during WWII were converted from refrigerated goods carriers because they were a few knots faster than other types. The North Korean types I mentioned would inevitably be very limited in the types of ship they can chase down because of the limited resources North Korea has for shipbuilding - according to Planeman's guide as small as 5,000 tons - and would likely go after trawlers and other vessels of like speed and size (which are not only rather important to Japan's economy, but would be likely disguises for intelligence gathering ships which the North Koreans would make a priority of hunting down and not be too indiscriminate of who they think is really a spy). You don't have a lot of options today - merchant ships have a uniform slow speed because it's economical that way, and if you need something shipped quickly it's more economical to do it by plane. You'd probably be looking at about a 10-year old, 20,000-30,000 ton fast ferry or cruise ship, even.
Like I said, the best pirate deterrent would be to have an escorting frigate. The second best pirate deterrent would be to have trained anti-boarding teams aboard. Since most pirates are limited by the ranges their naked eyeballs can spot at, a high-powered sniper rifle with high-quality optics kept in a weapons locker would be about as good as a 5-inch gun.