Hi Paul and Colin. Paul, the beautiful model in the picture is a different variation and doesn't seem to have the compass structure, but thanks for the link, I've not seen that one before.
Colin, yes I started with Johns plans and chose a different prototype. The hull and general arrangement are the same, but a lot of detail is different, most obviously the gun turrets are open, no domes on them.
You have pinpointed my problem with the compass, no detail. If I end up guessing I'll make the mount and plonk a compass on top, but I bet that's not right. I can't imagine the crew shinning up to the compass to get a bearing, but I bet new crew were told to.
Chas