My 2 pesos here...
Sadly, you're going to be doing a lot of reloading to get that one crucial hit on a KGV that disables all of its propulsion. I'm not quite sure how the game models it, but the real KGV had quite compartmentalized machinery as in this image
(link, top profile) The inner and outer screws were controlled by boiler and machinery rooms with a good amount of separation. You would need to strike at the weakest point - where all four shafts exit the hull. Again, a very difficult shot. Then you need to strike the ship a second time to ensure a sinking. One shot will be unlikely to have enough of an effect on a stationary target, especially something so well-armored.
The Nelsons might be arguably more difficult through the same strategy - sure, there's only two shafts, one main machinery space, one main boiler space. But you must also remember that they were considered the epitome of the "all or nothing" armor scheme. In other words, the propulsion system is very, very heavily armored. The unarmored sections were designed to not impair seaworthiness dramatically if flooded. A single, secondary shot will again likely have little effect unless you stay on the site for a very, very long time.
Your better chance of gaining some renown is to take out a cruiser. Sure, they're not worth as much a battlewagon, but they are much more likely to sink from two eels. It would be best to either to guarantee a sinking than to gain no credit for damaging a target. And of course, this is assuming you survive your raid.