The vowel sounds are the most vexing source of errors, especially where diphthongs are found.
"The Art of Public Speaking"
Dale Carnagey (AKA Dale Carnegie) and J. Berg Esenwein
W. Of w, which in diphthongs is often an undoubted vowel, some grammarians have doubted whether it ever be a consonant; and not rather as it is called a double u, or ou, as water may be resolved into ouater; but letters of the same sound are always reckoned consonants in other alphabets: and it may be observed, that w follows a vowel without any hiatus or difficulty of utterance, as frosty winter.
"A Grammar of the English Tongue"
Samuel Johnson
For the semivowels and the diphthongs, see the sequel.
"The English Language"
Robert Gordon Latham