There is the weekend punt service from Westgate park on Todd Road - next to the go kart track near westgate bridge
Used heaps by cyclists (even trialled as a short cut for commuting cyclists cuppla years ago):
Comes across near Scienceworks in Newport right next to the bike path that takes you out to Altona
$5 return maybe?
Ride from the city along South Wharf - lorimer street (quiet on weekends but has onroad bike lane and then converts to bike/ shared offroad footpath) - todd road - right into westgate park
South of jeff's shed there is the bike path that runs alongside the light rail to station pier and you can then turn right @ Port Melb d'lish fish and take it along the beach around to Westgate park (thus avoiding onroad riding) - but assume this is a longer less direct route)
Once you get to Westgate park - look for the signs painted on the concrete path with directional arrows.
I think you ring the mobile on the signs @ the landings to collect you if it is on the other side of the river.http://www.westgatepunt.com/http://www.bv.com.au/general/bikes-and-riding/11690/