Steve-
The comments from Don (Sneaks) are good ones!
Do you launch mostly at the same ramp all the time? If so, when you get it just right, mark some convenient easy to see place on the trailer with a pen or tape so you can repeat the "just right" launch depth for that ramp.
There are problems when encountering very steep or shallow ramps.
Steep ramps sink the rear of the trailer when the front is at the optimum height, and you may have to learn to leave the front of the trailer a little higher than ideal under normal situations in order to avoid having the boat wander over the rear of the trailer and perhaps come up crooked when finally pulled out. With the front higher than normal, you may have to rely on the winch to pull the boat fully onto the trailer.
Shallow ramps have the opposite problem. The front of the trailer is very far out of the water while the rear is still too high to float the boat over. Here you may have to back in deeper, if possible, to get the rear submerged enough, and still use the winch to pull the boat forward to the front bow fitting over a nearly horizontal trailer.
Either of these two scenarios is easier with two or three people as you can get some serious help at changing the depth of the trailer in the water with the tow vehicle, handling the bow of the boat as it enters the front of the trailer and doing the winching, and driving the boat onto the trailer and using the motor thrust to assist in pushing the boat onto the trailer.
This brings us to the discussion of driving the boat onto the trailer, either alone or with help. If you're alone, you usually leave the trailer at a slightly higher level than when launching, so that when you force the boat up onto the bunks, it will rest weight on them and stay "stuck". You then climb over the bow and attach the winch and safety chain. With a second person, the boat doesn't have to be driven as "hard" onto raised bunks, as that person can clip the bow onto the winch and fittings.
The problem is that there are so many different possible launching situations that the solutions are nearly endless.
Sometimes there's no floating dock present. Sometimes strong winds or currents complicate matters. Sometimes there are traction problems on the ramp.
Sometimes the ramp is paved all the way down past where your trailer will go, but most ramps end the pavement and then abruptly drop off into slippery mud which is 1-2 feet lower than the end of the pavement.
Dropping your trailer wheels into this hole is problematic, dropping your tow vehicle's rear axle into it is catastrophic!!! Don't ask me how I know, but when the salt water in your Volvo reaches your butt in the driver's seat, you'll wish you knew about this phenomena and hope that most ramps have a line and a sign at the point marking the end of the ramp.
Roller trailers are a somewhat different ball game, but they actually make the shallow and deep ramps a little easier to accommodate as they permit you to keep more of the trailer out of the water and use the winch to pull the boat onto the trailer. Driving onto the trailer by yourself in the boat, however, is much more difficult.
There are just so many different situations and ways this whole process can be done that the best thing is to get as much experience as possible in as many different situations, and then be flexible and creative to try as many different solutions as are needed.
Often you just have to wade out into the water to get the danged boat on the trailer right. Shorts, hip boots, what would you need?
A platform of 1/2" marine plywood up in the triangular area of the trailer allows you to walk around on the front of the trailer and out of the water. Widening the trailer tongue and / or adding non-skid to the tongue can help, too. A power winch works for some. A really good set of guide-ons helps out tremendously. The front padding shown by Sneaks can be replaced by a wide roller, if needed. The list goes on and on.....
Hope this is helpful! Joe.
