RiffRaff said..
WA DOT Website indicates the following do not need to be registered
Yachts, canoes, surf skis and other craft without motors are not required to be registered.
Tenders to larger vessels are also exempted, provided they:
1. Are no longer than 3.1 m
2. Have engines no bigger than 3.73kW (5hp)
3. Are used only as lifeboats and for ship-to-shore transport.
The only thing with a tender, is it is to be used from larger boat to shore only. Technically you can't even run to another boat with it.

Yes boats Chris

Mitchbat even if it has an hin number, that number needs to be registered and if not then you need the certificate..
Having said that cheap inflatables can be an nightmare..