A search for a massive W ′ gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in pp collisions at the LHC. The dataset was taken at a centre-of-mass energy of s √ =8 TeV and corresponds to 20.3 fb −1 of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass W ′ bosons in the range 1.5–3.0 TeV . b -tagging is used to identify jets originating from b -quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the W ′ →tb cross section times branching ratio ranging from 0.16pb to 0.33pb for left-handed W ′ bosons, and ranging from 0.10pb to 0.21pb for W ′ bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the W ′ -boson coupling to tb as a function of the W ′ mass using an effective field theory approach, which is independent of details of particular models predicting a W ′ boson.