It's the lack of reference points. In this situation, I do my adjustments while moving forward, and only back up straight. That allows me to use the dock door, itself, as my reference, because I can see it in both mirrors, as I back up to it, and I already know that the truck is lined up, before I start backing in. I've got 40 acres in front of me; might as well use it...
THAT - the lack of any guide what so ever but the trailer tail and the dock bumper will throw me off everyday. Even one line - sight-side - is better than chase & correct for 15 minutes. I'm half expecting someone to run out and say 'You're on candid camera!'
If there are no lines on the ground, you can make your own. Take some upside down orange paint can and put a dot of paint directly below the bumper pad on the dock, spot of paint on the ground right there. Measure over 3 feet along the dock and make another paint dot. From the second dot, pull the tape 4 feet toward where the long dock line would be. Paint a semi circle arc at the 4 foot mark. Now pull the tape from first dot 5 feet out and make another semi circle arc over the first semi circle arc. Where they cross is 90 degrees to the dock. Now pull a stringline from first dot through the insterction of the semicircle cross about 50 or 60 feet out from the docks and paint the string. Now you have your dock line on the ground to line up against.
upside down construction paint is bio degradeable and will be gone in a few days. This is the method the Egyptians used to lay out the Pyramids. If you go on google maps and look at the pyramids and line them up in each corner of your screen you will see that they are all perfectly square and also aligned perfectly north south. Yet the modern human cannot even hit a wide open dock lol
If im having a bad go of it in a open field situation, ill just ally dock it and be ###### where my tractor ends up.
having to to do an extra pull-up to straighten up or move over a little is a far cry from going full surveyor mode to draw lines. i would hardly compare pyramid construction to backing a truck into an unmarked dock. still lol'ing....