  We study multilayer triangular lattice Ising antiferromagnets with interlayer
interactions that are weak and frustrated in an abc stacking. By analysing a
coupled height model description of these systems, we show that they exhibit a
classical spin liquid regime at low temperature, in which both intralayer and
interlayer correlations are strong but there is no long range order. Diffuse
scattering in this regime is concentrated on a helix in reciprocal space, as
observed for charge-ordering in the materials LuFe$_2$O$_4$ and YbFe$_2$O$_4$.
