First of all, as others have already indicated you should tip with cash. It is just easier for you and the person performing the service. However, consider the reason why you are tipping. Also, consider how much you have already tipped before you set foot on board. If the math adds up or you received excellent service and want to show your appreciation it, go for it. Nothing wrong with that.
There is nothing wrong with tipping extra. All things being equal, the bulk of the passengers you will be rubbing shoulders will be paying the same built in service/charge gratuities as yourself. This means that everyone is equal in terms of how fast the bartender will get your order. Tip after all stands for To Insure Promptness. Therefore, you must tip cash in order to be served quicker. That is the only reason I tip. Below is why. the example is from the 15 Panama Canal on this Bliss this November.
After you remove air fare, the vibe, and taxes/port fees, etc the cost to set foot on this ship is $1049.
I remove those items from consideration because they have nothing to do with service on the ship except for the vibe which has a fee attached to cover this added level of service.
There are $644.80 worth of fees tacked onto that $1049 which means tips, DSC, account for 61% of the voyage fare. Now I don't know exactly how the money is divided up between NCL and the crew but I am only tipping if the service is slow, and I hope to speed it up. It works on every cruise with NCL I have ever been on. If you flash cash, they will serve you faster and more often that those that don't.
