  It is well known that a combined analysis of the Sunyaev-Zel'dovich (SZ)
effect and the X-ray emission observations can be used to determine the angular
diameter distance to galaxy clusters, from which the Hubble constant is
derived. The present values of the Hubble constant derived through the SZ/X-ray
route have a broad distribution ranging from 30 to 70 km s^-1 Mpc^-1. We show
that this broad distribution is primarily due to the projection effect of
aspherical clusters, which have been modeled using spherical geometries. The
projection effect is also expected to broaden the measured gas mass fraction of
galaxy clusters. However, the projection effect either under- or overestimate
the Hubble constant and the gas mass fraction in an opposite manner, producing
an anticorrelation. Using the published data for SZ/X-ray clusters, we show
that the current Hubble constant distribution is negatively correlated with the
measured gas mass fraction for same clusters, suggesting that the projection
effects are present in current results. If the gas mass fraction of galaxy
clusters, when measured out to an outer hydrostatic radius is constant, it may
be possible to account for the line of sight geometry of galaxy clusters.
However, to perform such an analysis, an independent measurement of the total
mass of galaxy clusters, such as from weak lensing, is needed. Using the weak
lensing, optical velocity dispersion, SZ and X-ray data, we outline an
alternative method to calculate the Hubble constant, which is subjected less to
projection effects than the present method based on only the SZ and X-ray data.
For A2163, the Hubble constant based on published SZ, X-ray and weak lensing
observations is \sim 49 \pm 29 km s^-1 Mpc^-1.
