Seeking assistance, please, with:
1 down 17 arranged to cover a No 1 hit for instrument (7 letters) P---O--
13 down Explorer, say, and channel swimmer met various rowers (two words) 3and 7 letters. -E- B-O-S-R
23 down Look! It's essentially cheap and tawdry art (6 letters) -I-S-H
and finally, 14 across Quiet fellow cracks a cryptic clue after training (8 letters) P---E-AL