### Clue: Briefly try tool starting engine on riverboat (7)
### Answer: TRAWLER 
 ### Explanation: Definition: boat 
 "try " **minus its last letter**(Briefly …) + AWL(a tool for pierceing) + **the 1st letter of**(starting) "engine " **plus**(on, in a down clue) R(abbrev. for "river").