Well, what can I say about this one? Phi has made his theme fairly obvious (unless I’ve missed something more devious).
A rapid solve for me, with the NE quadrant being completed quickly before progressively moving round the grid clockwise. I had not solved 29 when I entered 6dn but when 13ac went in a minute or two later it became clear what the HH represented. This meant that the other clues referencing 29 were rather easy to parse. Thanks, Phi, for the entertainment.
Across
1 Put paid to / beauty contest winner? (4)
DISH – double def.
3 Soprano with endlessly vocal jazz fans carrying 29 types of headwear (6,4)
SLOUCH HATS – S (soprano) LOU[d] (endlessly vocal) CATS (jazz fans) around (carrying) HH (29)
10 29 in universities heading for Humanities, I suppose (2-3)
UH-HUH – HH (29) in U U (universities) H[umanities] (heading for Humanities)
11 Royal attendants about to receive English vegetable (9)
COURGETTE – COURT (royal attendants) around (about) GET (to receive) E (Engllish)
12 Army turned about, having seized large weapon-carrier (7)
HOLSTER – HOST (army) RE (about) reversed (turned) around (having seized) L (large)
13 Pile of rubbish apparently includes 29, in the main (3-4)
ASH-HEAP – AP (apparently) around (includes) HH (29) in SEA (the main)
14 Maroon was released by traveller afloat? (9)
OARSWOMAN – an anagram (released) of MAROON WAS
17 Manage to retreat, getting hard time (5)
EPOCH – COPE (manage) reversed (to retreat) H (hard)
19 Half-hearted attempt to start up a new form of transport (5)
SEDAN – SE[e]D (half-hearted attempt to start up) A N (new)
21 Port frequently given a poor rating? (9)
LOWESTOFT – LOWEST (given a poor rating) OFT (frequently)
23 Male I leave, around 29 – what does it matter? (5-2)
HEIGH-HO – HE (male) I GO (I leave) around HH (29)
25 Article’s effusiveness about one in pain (7)
ANGUISH – AN (article) GUSH (effusiveness) around (about) I (one)
27 Awful expression of annoyance creeping into tense employment arrangement (5-4)
THIRD-RATE – DRAT (expression of annoyance) in (creeping into) T (tense) HIRE (employment arrangement)
28 Most of all, I attempt to overlook daughter’s justification (5)
ALIBI – AL[l] (most of all) I BI[d] (attempt to overlook daughter)
29 Mat, according to online comments, is a feature of sport (5,5)
RUGBY POSTS – RUG (mat) BY (according to) POSTS (online comments)
30 Supports keeping half back for gala (4)
FETE – FEET (supports) with the second half reversed (keeping half back)
Down
1 Servicemen ready with marine markers, we hear (9)
DOUGHBOYS – DOUGH (ready {money}) plus a homophone (we hear) of BUOYS (marine markers)
2 Student of the sun, pinning down carbon and hydrogen (7)
SCHOLAR – SOLAR (of the sun) around (pinning down) C (carbon) H (hydrogen)
4 March and rally heading off wrongly, prompting tears (9)
LACHRYMAL – an anagram (wrongly) of MARCH [r]ALLY
5 Usual changes, not special, but very necessary for part of mouth (5)
UVULA – an anagram (changes) of UsUAL with the s (special) changed to V (very)
6 Wells, say, including one with 29 fish – soles of extended size (4,5)
HIGH HEELS – HG (Wells, say) around (including) I (one) HH (29) EELS (fish)
7 30s style rated ‘dreadful’ by company (3,4)
ART DECO – an anagram (dreadful) of RATED plus CO (company)
8 Goes climbing, securing line – try dropping off? (5)
SLEEP – PEES (goes) reversed (climbing) around (securing) L (line)
9 Close call, nothing less (4)
SHUT – SH[o]UT (call, nothing less)
15 Succeed with energy and light, enthralling Newton (3,3,3)
WIN THE DAY – WITH E (energy) DAY (light) around (enthralling) N (Newton)
16 Supplier of information: green pond’s third to be circled by amphibian (9)
NEWSAGENT – SAGE (green) [po]N[d] (pond’s third) in (to be circled by) NEWT (amphibian)
18 Thick, i.e. daft, to carry 29 in travel by road (5-4)
HITCH-HIKE – an anagram (daft) of THICK I.E. around (to carry) HH (29)
20 Vigorous water sport held around river (7)
DRIVING – DIVING (water sport) around R (river)
22 Soldiers, if leading reserve, will get opening (7)
ORIFICE – OR (soldiers) IF ICE (reserve)
23 No repeat appearance for milliner one dislikes (5)
HATER – HAT[t]ER (no repeat appearance for milliner)
24 Cheers success in support of old NZ university (5)
OTAGO – O (old) TA (cheers) GO (success)
26 Vessel almost capsized in capture (4)
GRAB – BARG[e] (vessel almost) reversed (capsized)
I loved it-I quickly sussed the HH in certain clues way before getting 29.You will not find “rugby posts” under HH in Chambers.
Very neat stuff.
Yes, a neat conceit. Not one my quickest. I didn’t get 29 for ages which was like driving with the hand-brake on. Also 6d had me struggling and then irritated; I thought my working solution of ‘snow shoes’ fitted the ‘soles of extended size’ better. (Still do, actually)
Clever & challenging, just what we like. Thanks to Gaufrid [small lit in 4, sorry to mention it, sir] and to Phi once again.
Thanks Grant, typo now corrected.
Good fun. I was another who had worked out the ‘HH’ bit before solving 29. Liked HIGH HEELS and ART DECO – the wordplay for the latter strikes a chord with me!
Thanks Phi and Gaufrid.