Either catch the district line to Gunnersbury and walk (15 minutes) or catch the district line to Turnham Green, then take the E3 to Faukenburg Road and walk (5 minutes).
Catch the Hounslow train via Brentford Loop from Waterloo, Vauxhall or Clapham junction (for more stops contact BR) to Chiswick station. From here it is a 5 minute walk. From Station Approach Road turn down onto Grove Park Road and then turn right onto Hartington Road. The boathouse is on the left hand side of the road (the river side!).