There is a big long ceremony that must be done correctly. Above all, libations are to be consumed! Failing to do this will anger the gods. 
Here is the list ceremony from boatinghowto.com;
It was a common superstition among sailors that renaming a boat would condemn her to an early visit to the deep. This was the equivalent of removing her soul. However, as times have changed it has been found acceptable to accomplish this task as long as a strict regimen was followed that would appease the Gods.
There are actually two ceremonies and they can be as formal as you desire. They commonly range from a few spoken words to something a bit more elaborate complete with costumes and props. For those that truly love boating it is not uncommon for the ceremony to become a more involved affair with family, friends and dock-mates participating. So above all make it a fun event that the family will remember.
You will find various examples of the renaming ritual on the internet each with its own flavor, however they all follow a common sequence of events.
1. Removal of Previous Identity.
2. De-naming Ceremony.
3. Re-naming Ceremony.
Removal of Identity
According to legend, every vessel is recorded in the Ledger of the Deep by Neptune. Should Neptune find a vessel plying the waters that is not properly listed in his ledger, they shall suffer his wrath, after all this is his home.
Therefore, this is perhaps the most critical step in the ritual to ensure you start off on good terms. All items bearing the old name must be removed from the vessel; this includes logbooks, paperwork, key-chains, and other items. It is easy to overlook something so take your time and garner the help of others to ensure this is done properly. This may require the use of white out or a black marker for the logbook if you plan on keeping the former one. Poseidon will not purge the old name from his records as long as any evidence of it remains so be diligent.
Furthermore, during this process do not mention the new name or place any items bearing the new name on the boat. This is considered very offensive and being presumptuous to assume Neptune will grant your request before you have even asked.
Once all evidence of the old name is removed, you will need to secure several bottles of wine and a small metal tag or ingot. The amount of wine will be determined by the amount of guests that will participate in the ceremony but at the very least you will need three bottles. One bottle will be sacrificed to the gods during the denaming ceremony and two for the renaming ceremony. On the small metal tag (ingot), you will write the boat's old name with a water-soluble pen. This tag (ingot) will be part of the denaming ceremony. Many people will substitute champagne for wine during the ceremony; however, wine is embedded much deeper in the history of vessels and the sea than champagne.
De-naming Ceremony
Now is the time to round up all of your guests to take part in this momentous occasion. It is a good idea to explain the importance of these ceremonies and ask that the guests remain quiet to show their respect and pay homage until both ceremonies are complete. Only your immediate family should be onboard and allowed to perform the ceremony, your guests should observe the proceedings from the dock or a nearby boat. The denaming ceremony's purpose is a plea to Neptune to remove all traces of the old vessel's name from the Ledger of the Deep.
Now with your ingot and bottle of wine proceed to the bow of the boat and you are ready to begin.
Oh mighty and great ruler of the seas and oceans, to whom all ships and we who venture upon your vast domain are required to pay homage, implore you in your graciousness to expunge for all time from your records and recollection the name (insert the old name of your vessel) which has ceased to be an entity in your kingdom. As proof thereof, we submit this ingot bearing her name to be corrupted through your powers and forever be purged from the sea. (the metal tag is dropped from the bow of the boat into the sea.)
In grateful acknowledgment of your munificence and dispensation, we offer these libations to your majesties and your court. (open the wine and pour at least half the bottle into the sea beginning in the east and moving to the west, the remaining wine can be shared after the ceremony)
At this point, it is absolutely imperative that the boat's old name never be spoken again in the presence of the vessel. She is clean and nameless with homage paid to Neptune. In most cases, you should immediately proceed to the naming ceremony since your vessel is now unknown and unprotected.
Additionally, do not bring any items bearing the new name on board the vessel, nor mention the new name in the presence of the vessel until the naming ceremony is completed. If the new name must be applied to the transom prior to the ceremony, it must remain covered and hidden from view until the end of the ceremony.
Naming Ceremony
The naming ceremony consists of two parts, first a plea to Neptune to record the new vessel name in the Ledger of the Deep, then the second part pays homage to the gods of the wind.
Now with a fresh bottle of wine proceed to the bow of the boat and prepare to begin.
Oh mighty and great ruler of the seas and oceans, to whom all ships and we who venture upon your vast domain are required to pay homage, implore you in your graciousness to take unto your records and recollection this worthy vessel hereafter and for all time known as (new vessel name), guarding her with your mighty arm and trident and ensuring her of safe and rapid passage throughout her journeys within your realm.
In appreciation of your munificence, dispensation and in honor of your greatness, we offer these libations to your majesty and your court. (open the bottle of wine, pour one glass for the Captain and one glass for the First Mate but don't drink yet, now pour the remainder of the bottle into the sea from West to East, then drink your wine.)
For this part you will need another bottle of wine and a small glass.
Oh mighty rulers of the winds, through whose power our frail vessels traverse the wild and faceless deep, we implore you to grant this worthy vessel (boat’s new name) the benefits and pleasures of your bounty, ensuring us of your gentle ministration according to our needs.
(Facing north, pour wine into the glass and fling to the North as you intone.)
Great Boreas, exalted ruler of the North Wind, grant us permission to use your mighty powers in the pursuit of our lawful endeavors, ever sparing us the overwhelming scourge of your frigid breath.
(Facing west, repeat and fling to the West.)
Great Zephyrus, exalted ruler of the West Wind, grant us permission to use your mighty powers in the pursuit of our lawful endeavors, ever sparing us the overwhelming scourge of your wild breath.
(Facing east, repeat and fling to the East.)
Great Eurus, exalted ruler of the East Wind, grant us permission to use your mighty powers in the pursuit of our lawful endeavors, ever sparing us the overwhelming scourge of your mighty breath.
(Facing south, repeat and fling to the South.)
Great Notus, exalted ruler of the South Wind, grant us permission to use your mighty powers in the pursuit of our lawful endeavors, ever sparing us the overwhelming scourge of your scalding breath.
And to the greatest of all, mighty Aeolus guardian of all winds and all that blows before them, we ask your favor and kindness for fair winds and smooth seas in our endeavors as we humbly pass through your kingdom.
If the new name has been affixed to the transom, it should be unveiled at this time. If it has not been affixed bring an object aboard bearing the new name to complete the ceremony. Of course at this point applause and cheers should abound as your vessel now has her new identity and everyone can join the celebration.
Be sure and take lots of photos and record the event along with all the details in the vessel's logbook. Now you can share a sigh of relief and rest assured that your vessel is assured a safe journeys.
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