I worked offshore Vung Tau around 20 years ago, caught the hydrofoil HMC/Vung Tau once a month.
The ferry was a great journey, had a bar on board, at times would stop and reverse to remove debris from the intakes.
After I left Vung Tau, they built a road, tunnel through the mountains, I don't think the hydrofoil is an operating anymore.
Vung Tau is a nice location, on the beach, trendy city. I've got a few co-workers still living there .