Saterfrisian has a four-step system of shorts: ie           uu     üü   i       u     ü       ä   o     ö           a

and of longs: íe           úu     ü'ü   ee       oo     öö       ää   oa     öä           aa

as well as the diphthongs ending in i:                                         äi   oi oai   öi         ai

and the diphthongs ending in u, uw: ieuw                     eeuw                     äuw   ou                 au

Saterfrisian has thirty vowel phonemes, like West Frisian. But they are quite different.
For a possible explanation of this large difference see A phonematic catastrophy.

The difference between ie and íe respectively uu and úu as well as üü and ü'ü only applies for e few words.