1. Yes, the 0.66 means the equipment is 66% damaged. 1 means the item is beyond repair (unless you hired that mechanical guy that can fix even those equipments
)
2. The sonar and radar sensors on the ships are the same in the daylight and at night. The performance of the visual "sensor" is proportional with the amount of light, on all ships (including yours)
1. The navigation map grid is configured from the data\Menu\KGrid\KGrid.cfg file. I'll ask if there is anything that can cancel it.
2. You can't really expect to sink a merchant with AA bullets. I think that not even a million of those won't help.
3. I've been offered to dock in Surabaya while being miles away, with nothing in visual range.
4. That is standard SH3 behavior for the German uboats.