why w and y are called semi vowels
Semivowel In phonetics and phonology, a semivowel or glide, also known as a non-syllabic vocoid, is a sound that is phonetically similar to a vowel sound but functions as the syllable boundary, rather than as the nucleus of a syllable.[1] Examples of semivowels in English are the consonants y and w, in yes and west. Written /j w/ in IPA, y and w are near to the vowels ee and oo in seen and moon, written /iː uː/ in IPA.
H For most English speakers, the name for the letter is pronounced as /eɪtʃ/ and spelled 'aitch'[1] or occasionally 'eitch'. The pronunciation /heɪtʃ/ and the associated spelling 'haitch' is often considered to be h-adding and is considered nonstandard in England.[2] It is, however, a feature of Hiberno-English.[3]