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Ongoing Saga of the Christina B
Valid points. "Air gapping" the navigation and control systems does provide a level of security and intrusion prevention... I can't disagree.
And while I can think of a couple of mechanisms that would/could dramatically reduce the probability of being "hacked" or denied of service.... none are 100%.
And I would imagine that this has been one of the reasons why so many internet devices and systems have gone the way of the "cloud interface", so the manufacturer can control both ends of the communication scheme, injecting their security smack dab in the middle.