It seems simple, but usually on the ramp of my port (Spain) I see as generally trailers submerging it into the water until the rib is afloat, wetting shafts, bushings, brake systems etc.
Salt water is very harmful to all those delicate parts and even the systems that are declared "watertight" , if you want your trailer will last many years without spoiling and are using to launch your boat in salt water, it is very important not but only wet the shaft rubber wheel, then it can be good rinse thoroughly with fresh water, because the salt water of the tires to spin may have something other parts wet.
Should be given back slowly up and if anyone can advise you to stop the trailer when the wheel is wet only the height of the rubber nothing else, but no one to warn you, you can stop and watch if you have to go down a little more.
Nor is it good to leave too separated from the water because it can hit the hull with the bottom having not enough water when you let fall the rib.
Another detail that generally few use is tying two ends to the bow and stern of your boat, the stern can be very useful if the wind pushes the boat against the trailer, or the slope of the ramp is insuficient and , the boat does not fall to the sea.
Pulling out this rope, you can help the boat to glide smoothly and free from trailer. No seen in the video because it was not necessary to use but it is convenient to have it always be prepared just in case.
The rope of the bow is always used , as you can see in the video when you start the descent down the trailer into the water, then serves for approaching the dock the boat and tie it conveniently.
It is very important good braking the tractor trailer, if the boat is very heavy also put chocks on the wheels of the vehicle can keep your rib car takes to water!
I imagine all people know this, but may be useful for someone new...