Western Ferries offers a car ferry service to Dunoon. Sailing every 20 minutes on the hour.
See fares and timetables, as they differ during the year.

Glasgow Airport to either ferry destination is a 40 minute drive.
https://www.western-ferries.co.uk/
https://www.calmac.co.uk/en-gb/route-information/gourock-dunoon/#/

Ferry Tickets
Tickkets can be purchased onboard or from the following locations:

Co-op
21 Eldon St, Greenock PA16 7UG

Lido Community Shop and Post Office
43 Shore Rd, Innellan, Dunoon PA23 7TJ

Buying ferries onboard is more expensive, try to buy before you get on.

Leaving the Ferry
Coming from either the car ferry at Hunter’s Quay, or the small ferry in Dunoon, the direction is the same. Turn left and drive out towards Innellan. One you get to the village of Innellan, keep driving through and continue along the shore. Soon you will be at Toward Point. Super easy.