Best trailer depth for launching and retrieving a boat

How deep should I have my trailer to launch and retrieve my boat?
Here's a general guide to follow, although (obviously) it may vary depending on the depth/angle of your local boat ramp, as well as the tide at the time.
Check out the Bar Crusher website - www.barcrusher.com.au - for more information and use the online boat builder to spec-up your Fishing Weapon!