The steward is included in the $10 per day. Carnival does not have "head waiters" (Royal Caribbean does). There is an assistant waiter, a waiter and then the maitre d'. The maitre d' is a management position and there is no need to tip him or her unless (s)he does something for you (beyond saying hello).
Here is Carnival's tipping policy ...
What is the tipping policy onboard?
Service Gratuities
For your convenience, we automatically charge the gratuities for dining and stateroom staff to your onboard Sail & Sign account. The total amount is $10.00 per guest, per day (our recommended guideline) as follows:
$ 3.50 Per Day Stateroom Services
$ 5.50 Per Day Dining Room Services
$ 1.00 Per Day Alternative Services: distributed to other kitchen and hotel service staff
For Cruises-To-Nowhere, gratuities of $10 per guest, per day must be prepaid.
Our Staff is totally committed to exceed your expectations in every way possible. If you are not satisfied with the service you receive, we encourage you to contact the Purser’s Information desk while onboard. This will allow us to address your concerns in a timely and appropriate fashion. At your discretion, you may adjust the gratuities at any time.
For beverage purchases, fifteen percent of the bill is automatically added to the Sail & Sign charge. Room Service staff may be tipped as service is rendered. Tipping your Maître d’ is at your discretion, based upon the service you receive.
Here is a link ...
http://www.carnival.com/CMS/FAQs/Gratuities_Tips.aspx
