A similar question was asked last month and here is where it stands that we've/ last heard.
Read Jamie's post 1/3 of the way down:
Here
Sonalysts has stated that Dangerous Waters did not meet their sale expectations and wasn’t considered a financial success, so I doubt we will see further add-ons. They are still working on another patch, but they have to focus on more profitable areas with their non-commercial and government contracts. This is why it’s been 9 months since the latest patch was released. As far as another game? I doubt it, or at least not very long time.