I used to own a 26ft sailboat with a swing keel and 80gals of water ballast.
Getting it on the trailer was a bugger as it only had a 6hp aux. Trailer depth in water was critical.
Ended up mounting a depth guide pole on the trailer mudguard that I could see from the car side mirror. Drive the boat onto trailer( usually crabbing) untill about 1 ft from bow roller, secure winch cable and tighten, haul out just clear of water, open drain valve and drain, close valve and winch all the way up. This took some time and , of course I was not always the most popular guy on the ramp.