Learn Finnish: Minulla ei ole varaa ostaa uutta purjevenettä.

In Finnish, expressing that you have the means or capability to do something often uses the possessive structure (minulla on or minulla ei ole) plus a resource noun in the partitive case. Here, the noun is vara (wealth, means, or reserve). Put together, minulla ei ole varaa literally translates to 'on me is not of means,' which is the standard way to say 'I cannot afford'.

Why is the object of the buying, uutta purjevenettä, in the partitive case?

The partitive is used here because the main clause is negative (ei ole). Even though the object belongs to the infinitive verb ostaa, the negative scope of 'not having the means' covers the whole action. In Finnish, if the overarching action is negative, the object of the verb must be in the partitive case.

If I changed this to a positive sentence ('I can afford to buy a new sailboat'), how would the object change?

In a positive sentence, the object would change to the nominative-looking accusative: Minulla on varaa ostaa uusi purjevene. Because the possessive structure (minulla on) does not have a grammatical subject in the nominative case, the total object of the attached infinitive takes the basic nominative form instead of the genitive 'n' form.

Could I just use the verb voida (to be able to) to express this?