There are hire companies who will provide all equiempent required. See ski.com.au/activities for further information on these activity companies
There is a catamaran hire place at Lake Jindabyne, at the boat ramp near Paddy Pallins. There are boat ramps on Lake Jindabyne and Lake Eucumbene. Launching a trailer-sailer and exploring the lakes would be an unusual few days for a sailing holiday.
The lakes are extensive and would be a fine place for pottering in a tinny or more substantial craft. Lake Blowering is an ideal place for attempts on the world speed record for boats, if you are that way inclined.
Mt Beauty Pondage is small but suitable for a small dinghy.
Rocky Valley reservoir at Falls Creek is much larger and suitable for a dinghy or catamaran. It is quite shallow in parts.
Lake Hume is vast, although the area can be severely reduced in drought times, and trees can be an issue. You are not allowed to use a yacht with toilet and berths.