The /ɑ/ vowel is usually spelled <ar> but we also find <ear> in heart, <a> in khan and the letter name R. The /u/ vowel is spelled <oo>, <ew>, <ui> in bruise, and <ou> in you.
This contrast is between two long back vowels which are fairly well separated in the mouth and distinguished by lip-rounding. It is unlikely to cause problems for learners.
There is one set of pairs involving a taboo word: khan/coon.
The density value is 2.21%. The pairs make 53 semantic contrasts, giving a loading of 57.6%.
Accra accrue baa boo baa'd booed baaing booing baas boos balm boom barb boob barbed boobed barbs boobs barn boon barns boons bath booth baths booths blah blew bra brew bras brews bras bruise brass Bruce Cali coolie Calne coon card cooed Carl cool carp coop carped cooped carping cooping carps coops car coo cars coos cart coot carts coots Chard chewed char chew chars chews charred chewed grave groove graves grooves ha Hoo half hoof halves hooves hard who'd harm whom harp hoop harped hooped harping hooping harps hoops hart hoot harts hoots heart hoot hearted hooted hearts hoots jar Jew jars Jews khan coon khans coons la lieu lakh Luke larn loon larns loons last loosed ma moo mar moo marred mood mars moos march mooch marched mooched marches mooches marching mooching Mars moos mart moot pa pooh raft roofed rah rue R's ooze scarp scoop scarps scoops shah shoe shahs shoes shard shooed spark spook sparks spooks ta too ta two tar two tars twos tart toot tarted tooted tarting tooting tarts toots Tsar zoo Tsars zoos yah you yard you'd
John Higgins, Shaftesbury, November 2009