Stationary ships invisible? (GWX)

[Convycmg]

Got round to making the transition from recently rediscovered stock game to an install of GWX3 and SH3 Commander. It never ceases to amaze me what technically minded enthusiasts are capable of; many many thanks to all of those involved.

Anyway, 1st patrol since the outbreak of hostilities and I manage to sneak into Scapa Flow to discover HMS Nelson at anchor. I manage to creep close enough that her smoke stack, bridge and aftmost main turrett completely fill my attack scope, but nothing comes up on the target recognition notepad or the navigation map. The destroyer I crept past on my way to greet Horatio shows up fine though (Gott im Himmel they're close--hope that's the 10x magnification).

I was able to fire straight ahead from my forward tubes with no apparent target data and still score enough hits to sink the Nelson this time, though I wonder why she never showed up as a target?

Sure this has been covered before but thanks to anyone who can be at all enlightening. And also, many thanks for the 'welcome aboard' after my first post in another thread.