Quick! To the Grammarmobile!

It's Pasi and Newfie's. You can take my word for it, I speak the language fluently since I was 18.

Double post.

Perfection said:

Well to confound it all it actually has an s at the end

So Curt and Chieftess' boat then?

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No, because "Chieftess" is a singular noun.

It's Curt and Chieftess's boat.

Unfortunately, this creates the ambiguity that it could Curt with the boat that belongs to Chieftess or the boat that belongs to both Curt and Chieftess. However, the alternative is also ambiguous:

It's Curt's and Chieftess's boat.

The above implies that two boats exist, one belonging to Curt and the other to Chieftess, that happen to both be identical to the one being discussed. However, many would interpret the above as one boat that belongs to both Curt and Chieftess.

English is just an ambiguous language.

Cuivienen said:

It's Curt's and Chieftess's boat.

The above implies that two boats exist, one belonging to Curt and the other to Chieftess, that happen to both be identical to the one being discussed. However, many would interpret the above as one boat that belongs to both Curt and Chieftess.

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huh... how so? Even if one expands it to "It's Curt's boat and Chieftess'(s) boat," one would assume that you are talking about one boat (owned by both Curt and Chieftess), since you're using the pronoun "It": hence refering to one boat.

superisis said:

huh... how so? Even if one expands it to "It's Curt's boat and Chieftess'(s) boat," one would assume that you are talking about one boat (owned by both Curt and Chieftess), since you're using the pronoun "It": hence refering to one boat.

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I think she means that saying that might indicate that you're looking at a boat of which Curt and and Chieftess own other exemplars. Like saying "Curt's and Chieftess's Ford" might mean that Curt and Chieftess each has a Ford that looks exactly like/is the same model to/etc. the one in question. It's probably a rarer, but still plausible, interpretation.

website said:

Apostrophes with Possessives of More than One Owner

To show that more than one person share the same item together, make only the last owner in the series possessive.

Examples: Ken and Larry's ice cream
(They share the same ice cream.)

John and Mary's pet cats
(They share the same cats.)

To show that there are similar items which are owned individually by different owners, make each owner in the series possessive.

Example: John's and Mary's pet cats.
(They each have their own pet cat or cats.)

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taken from here