For moving heavy cargo
For moving people
....
People enjoy going for a sea cruise, stopping every 2-3 days at another port, etc. Boozing it up in the nightclub, unlimited buffet.... etc.
But how many people line up at Southampton or New York to cross the Atlantic versus Heathrow or JFK out of utility?
Let's say it does take 7 days for an airship to cross the Atlantic - you have crew costs for 7 days (I guess you probably need 2 crews on 12 hours on/12 off...?). And entertainment wise it's going to be pretty boring, don't you think?
There are plenty of alternate fuels to keep the combustion engine running, we just don't *need* them yet, as petroleum is still cheap and available. No one is going to support such a slow method for transport - unless perhaps you are postulating the price will be 1/7th that of an aircraft ticket?
- GY