  A rope of carbon nanotubes is constituted of an array of parallel single wall
nanotubes with nearly identical diameters. In most cases the individual
nanotubes within a rope have different helicities and 1/3 of them are metallic.
In the absence of disorder within the tubes, the intertube electronic transfer
is negligeable because of the longitudinal wave vector mismatch between
neighboring tubes of different helicities. The rope can then be considered as a
number of parallel independent ballistic nanotubes. On the other hand, the
presence of disorder within the tubes favors the intertube electronic transfer.
This is first shown using a very simple model where disorder is treated
perturbatively inspired by the work in reference \cite{maarouf00}.
  We then present numerical simulations on a tight binding model of a rope.
Disorder induced transverse delocalisation shows up as a spectacular increase
of the sensitivity to the transverse boundary conditions in the presence of
small disorder. This is accompanied by an increase of the longitudinal
localisation length. Implications on the nature of electronic transport within
a rope of carbon nanotubes are discussed.
