I know I'm not alone in having had problems recovering the boat straight on a CLH trailer. Each summer over the past 3 years I've spent time staring at the trailer trying to understand why the boat never goes on straight. I've measured and adjusted various parts of the trailer, but to no avail. When viewed from behind the trailer, the boat always ends up too far to the right, even though for the first half of the recovery the boat looks to be centred.
This weekend I was thinking about this again and, without the boat on the trailer, noticed the rear rollers didn't quite point straight down the centreline of the trailer. I measured their heights and distance from the centre, etc, and everything looked fine. But the more I looked the more I felt that the "aim" of the pair of rear rollers wasn't straight down the centre of the trailer but was a few degrees to the right. Each end of the swinging cradle was bolted to the Trailer's A-frame's arms at the same point (7cm from their ends) but the rollers' aim seemed to be slightly off.
So before recovering the boat today, I loosened the clamp that attaches the right side of the swinging cradle (when viewed from behind the trailer) to the trailer and knocked it forward. I did this until the area between the rear rollers appeared to point directly through the keel rollers. In the end I knocked the right side of the cradle forward by 1.5cm.
When I recovered the boat it came on dead straight first time. I didn't even need anyone to push or pull on the boat during recovery, it just came on straight. That's the first time that's ever happened and I'm confident I may have fixed the problem.
While the swinging cradle is bolted correctly perpendicular to the trailer's A-frame, I suspect the A-frame is not quite correctly aligned with the trailer's centreline. I think the boat wasn't coming straight on to the trailer, and as the winch pulled the bow on to the centreline the stern pivoted across. Re-aligning the swinging cradle made such a dramatic difference today that I think this might have fixed the problem. Fingers crossed.... :-)