Preference 1: Disambiguation by type
Replaces the content of "Article titles for ships > Disambiguation"

If a ship's name is unique, or it can be considered the primary topic for subjects of the same name (see Wikipedia:Disambiguation#Is there a primary topic? for advice), it does not need to be disambiguated.

No other known ships or topics are named "New Carissa", so the article for the freighter New Carissa needs no further disambiguation.
The merchant brigantine Mary Celeste, famous for being found under sail but abandoned with no explanation, is considered the primary topic for that name.

If disambiguation from other topics is required, add the ship's type or role (or rig/sail-plan for sailing vessels) to the end of the article title in parentheses. No other forms of disambiguation are valid.

Santa Maria (carrack) to disambiguate from other topics named Santa María, not Santa Maria (ship) (refers to a full-rigged ship) or Santa Maria (1460)
Canberra (ocean liner) to disambiguate from other topics named Canberra, not SS Canberra (unless it can be demonstrated to be the ship's common name) or Canberra (steamship)
Girl Pat (trawler) to disambiguate from other topics named Girl Pat, not FV Girl Pat (no evidence that the prefix was part of the ship's common name)
USS Arizona (battleship) to disambiguate from other topics named USS Arizona, not USS Arizona (BB-39) (pennant/hull numbers are depreciated for article titles)

Prefixes should not be added to a title for the sole purpose of disambiguating articles.

If additional disambiguation is required, add the ship's year of launch to the disambiguation in the following form:

(<type>, launched <yyyy>)
USS Enterprise (aircraft carrier, launched 1936) and USS Enterprise (aircraft carrier, launched 1960), vs USS Enterprise (motorboat) (not USS Enterprise (motorboat, launched 1917), no further disambiguation needed as no other motorboats of that name)
USS Enterprise (1936 aircraft carrier) or USS Enterprise (1960)

If the year of launch is unknown or uncertain, use an appropriate confirmed 'milestone' date, and change "launched" to the appropriate context. 'Milestone' dates are important dates in a ship's construction and operational history, and include (but are not limited to) completion of construction, commissioning into naval service, entry into civilian service, acquisition or capture (Many of the fields at ((Infobox ship career)) deal with milestone dates, see Template:Infobox ship begin/Usage guide#Infobox ship career for further information on what they represent). Be careful not to use one milestone's date with another's descriptor: a ship commissioned or entering service in a certain year may not have been launched or completed in that year. Any date used in the title should be supported by reliable, published sources in the article itself.

USS Enterprise (sloop, captured 1775)
USS Enterprise (schooner, commissioned 1776)
USS Enterprise (schooner, built 1799)
USS Enterprise (schooner, launched 1831)

Do not be over-specific with the ship type in the title. (Note: This could be combined with the almost identical advice on type for class articles and split into a separate section)

aircraft carrier, not fleet aircraft carrier or nuclear-powered aircraft carrier

If a ship is identified as having been of different types or roles throughout its career, use the type the ship was best known for. Create redirects from other type disambiguators to assist in successful article location.

Canberra (ocean liner), with a redirect from Canberra (troopship)
Additional examples for clarification. Examples throughout the proposal/guideline would be modified to suit.
New Carissa, not New Carissa (freighter): no other subject with this name, so no disambiguation needed
Russian battleship Sevastopol (launched 1895) (Or, per Gatoclass's suggestion below, Sevastopol (battleship, launched 1895) )

May add more as necessary.

Preference 2: Disambiguation by contextual year
Replaces the content of "Article titles for ships > Disambiguation"

If a ship's name is unique, or it can be considered the primary topic for subjects of the same name (see Wikipedia:Disambiguation#Is there a primary topic? for advice), it does not need to be disambiguated.

No other known ships or topics are named "New Carissa", so the article for the freighter New Carissa needs no further disambiguation.
The merchant brigantine Mary Celeste, famous for being found under sail but abandoned with no explanation, is considered the primary topic for that name.

If disambiguation from other topics is required, add the year of the ship's launch to the end of the article title in parentheses. No other forms of disambiguation are valid.

Santa María (launched 1460) to disambiguate from other topics named Santa María, not Santa María (ship) or Santa Maria (1460)
Canberra (launched 1957) to disambiguate from other topics named Canberra, not SS Canberra
Girl Pat (launched 1935) to disambiguate from other topics named Girl Pat, not Girl Pat (trawler) or Girl Pat (1935 trawler)
USS Iowa (launched 1942) to disambiguate from other topics named USS Iowa, not USS Iowa (BB-61)

Prefixes should not be added to a title for the sole purpose of disambiguating articles.

If the year of launch is unknown or uncertain, use an appropriate confirmed 'milestone' date, and change "launched" to the appropriate context. 'Milestone' dates are important dates in a ship's construction and operational history, and include (but are not limited to) completion of construction, commissioning into naval service, entry into civilian service, acquisition or capture (Many of the fields at ((Infobox ship career)) deal with milestone dates, see Template:Infobox ship begin/Usage guide#Infobox ship career for further information on what they represent). Be careful not to use one milestone's date with another's descriptor: a ship commissioned or entering service in a certain year may not have been launched or completed in that year. Any date used in the title should be supported by reliable, published sources in the article itself.

USS Enterprise (captured 1775)
USS Enterprise (commissioned 1776)
USS Enterprise (built 1799)
USS Enterprise (launched 1831)
Additional examples for clarification. Examples throughout the proposal/guideline would be modified to suit.
New Carissa, not New Carissa (laid down 1989): no other subject with this name, so no disambiguation needed
Russian battleship Sevastopol (launched 1895)

May add more as necessary.

.