An abjad is a writing system in which only consonants are normally written, is the opposite possible? 

I've recently discovered that English actually has far more vowel-sounds than we have vowel characters (namely ~20) this is very similar to the number of consonant sounds (~24) so it seems to me that a writing system with only vowel should lose about as much information about word pronunciation as a writing system with only consonants.

obviously you would need more symbols for describing many different vowel-sounds rather than the English approach of ~ 5 vowel symbols

is there something i'm missing here which would prevent an anti-abjad from developing or is it viable?