Cryptic crossword - practise your lateral thinking!

12345678910111213
Across
  1. 3. Have understanding of a negative
  2. 6. An unheavy form of illumination
  3. 7. A medieval warrior in the dark
  4. 8. A healthy water hole
  5. 10. Push past a slow moving boat
  6. 12. A reduced price for a yacht
  7. 13. Send a wooden stick in the mail
Down
  1. 1. Left over from around your middle
  2. 2. Reserve some reading material
  3. 4. Lose the flame its job
  4. 5. Add a cost to a fast advance on the enemy
  5. 8. A heavy time in the queue?
  6. 9. Show the way to a heavy metal
  7. 10. A sport related dance?
  8. 11. Make fire on the pitch!
  9. 13. Go separate ways in the show