The combination of two techniques (Small Angle X-ray Scattering and Atomic Force Microscopy) has allowed us to measure in reciprocal and real space the correlation length ξ of salt-free aqueous solutions of a highly charged hydrophobic polyelectrolyte as a function of the polymer concentration C_p, charge fraction f and chain length N. Contrary to the classical behaviour of hydrophilic polyelectrolytes in the strong-coupling limit, ξ is strongly dependent on f. In particular, a continuous transition has been observed from ξ ∼ C_p^-1/2 to ξ ∼ C_p^-1/3 when f decreased from 100% to 35%. We interpret this unusual behaviour as the consequence of the two features characterising the hydrophobic polyelectrolytes: the pearl necklace conformation of the chains and the anomalously strong reduction of the effective charge fraction.