So, why “American Futharch” and not “British Futharch” or just “Modern English Futharch?”
Short answer: American English vs. British English has a particular “fault line” dividing them. That’s distinction in vowel length—short vs. long in the strict sense of length as time duration of pronunciation. British has it, American does not. And Eirik is a native speaker of American English.
Longer answer: Right now, you’re surely remembering all that stuff you were taught about short vs. long vowels in grade school—it was not because that was a “true” description of the reality of American sounds (it isn’t), but rather that it genuinely is helpful for making sense of the mangled spelling system. Words like rat/rate, bet/beet, bit/bite, rod/rode, run/rune make the point nicely, with how that “silent e” changes the sound.
What happened? In the early history of American English, distinctions in true vowel length were lost, and it can be thought about like this. (Though it is an extremely rough description!)
In the phonetic model I’m using, British English has two extra vowel rune-sounds, for a total of eleven—Armor and Udder (to give them names for illustrative purposes). They can be put into five pairs of short/long, with one unpaired short vowel.
When vowel length was lost in American English, you can think of it as the Udder sound merged with Earth (leaving Earth), and the Armor sound merged with Os (leaving Os). The remaining seven vowels remained distinctive from each other despite the loss of length. This left American English with its nine distinctive vowel runes, while British English retained those extra distinctions.
This is a bit of an over-simplification of what happened (and perhaps not technically the best description, nor completely correct), but it has the practical benefit that it’s a useful way to think about the differences between British English and American English, and why American speakers would not need those extra vowel runes. For instance, that the vowels of Udder and Earth aren’t truly “different” to American speakers, but they are to British Speakers, at least to speakers of Received Pronunciation, and that length is an important part of that difference.
Don’t sweat it if you can’t wrap your heard around it. It’s kind of like distinguishing between different shades of purple such as mauve, lilac, and violet—if you’re not making practical use of such distinctions regularly, you can get a sense of “what the heck are they talking about?” Or kind of like how you may have heard that certain insects see in ultraviolet light, which is invisible to us humans. What does UV light, which we can’t see, “look like?” Maybe purple, just more so? We can only speculate regarding the UV light and never actually know, but for those who train their ears enough, they can get a “flash of illumination” regarding the length distinction of the sounds—but even that took Eirik a while. The mysteries of speech sounds are many.
In any event, it’s not the focus of the American Futharch to formally incorporate those differences in British vowel pronunciation, let alone make any prescriptions about how such would be useful and used in runic esotericism. However, British speakers interested in experimenting with that are encouraged to contact Eirik. Same goes for Australian speakers. If you speak (American) English as a second language, feel free to give these runes a try and let Eirik know about it.