I think you have some very good advise here so far. Like everyone said there is a learning curve to each boat and trailer combo. On my 200XF the the keel at the bow is the deepest part in the water and it hits some of the trailers cross members so I have to dip the trailer deeper. On my 245 Explorer that is not the case, I have to keep the trailer shallower so the bunks will lift the bow so the pulpit will clear the winch. I do not drive the boat on either. I think it is too dangerous and then there is the whole washing out the ramp and kicking up silt into the motor or the water for the next guy. But hey thats just me.
Oh I just winch it on. I use a bow line to pull it to the trailer and then just winch it on. To be honest it easily winches right on. My bunks have the plastic on them so that may help it a bit.
I realize my 21 is much smaller and lighter but since I have only myself to launch and retrieve (drive truck and trailer) I've used this technique on both my 222CCP and my current WAC.On retrieval I have my son/wife/buddy watch as I back the trailer in and stop me when the trailer reaches the spot where water is just over the "pad" that is located in the pic above. While the pad isn't really seen in this pic, it resides between the two (one going each direction) little PVC "guides" (above the O on O'Neill on the trailer). This allows the helper to get the trailer at the depth I want without too much thought.Unlike most, I don't "drive" my boats on the trailer but rather pull them with the bow line. I have the winch strap already paid out and hooked to the roller bracket you see in front of the small guides. Then I just hook to the bow and crank the remaining way. By using a stern line and my "helper" I seem to be able to repeat the procedure every time even under windy conditions and while I may look the fool cranking the short distance. my boat sits on the trailer correctly each time.Maybe someday, I'll get a power "wench" :o for Christmas but no one really shares my boat fetish in my family.Good luck.