Roll On/Roll Off (RORO) shipping
RORO shipping is by far the most common method of shipping vehicles, it is the cheapest and fastest transport method typically, and indeed all new cars are shipped in this way by manufacturers. RORO ships are specially designed for this purpose with several decks within the belly of the ship designed to store vehicles during transit, and with a ramp for loading an dunloading with the cars driven on and off. Some modern ships even have adjustable deck heights that can be changed depending on if large trucks, farm equipment or other large vehicles might be shipped for that particular voyage.
Once driven onto the vessel cars are tied down with chains and tie downs, usually using the vehicles factory tow points as the main method of securement. Due to the rolling and movement of the ship on the water these tie downs are constantly checked throughout the voyage and each vehicle may be checked several times in total to ensure that there is no danger of the car moving. Vehicles are never shipped above decks where salt spray and exposure to the open seas may cause damage.
At the source and destination ports cars are typically stored in parking areas in a large queue.
For Australia there is typically a RORO ship available once every 3 weeks or so, for shipping to Fremantle in WA perhaps slightly less regularly. In Japan there are various booking and paperwork cutoff dates which are normally around 1 week before the vessel actually leaves, so this paperwork must be in and the car at the appropriate area at the port by this time to make the next vessel, and J-Spec handles all of this. Combined with an approximate shipping time of around 2 weeks and around 1 - 2 weeks for a car to be unloaded and clear customs and quarantine in Australia, the total time is around 5 weeks.