-- Last Updated: Sep-24-12 8:28 PM EST --
Even in my old age I can lift my kayaks over my head with two arms locked. I load the kayaks from the side of the vehicle, even my full size van.
The blocks are always positioned all the way to the side of the bars if I am carrying one or two hulls, unless I am using a really low vehicle like my Saab for one hull. This is so I can get the boats on the blocks from the side.
I stand next to the vehicle between the bars and either lift the whole kayak over my head onto both blocks at the same time, or I just lift the bow up onto the bow block first. I put the bow in the bow block with only a little sliding. Too much slide may rotate the bow foam block and knock it over, but that's okay as long as the bow is up there. I fix it later.
With the bow on the upright or knocked over bow block, I lift the stern with both arms onto the stern block. Then I go back to the bow, lift up the kayak an inch, and re-position the bow block under the boat.
You can even put the kayak on the blocks hull down, and then flip it over once it's up there.
I also have Thule Outriggers inside the Thule load bars on my high van, which can be extended outward to assist the side load. I would normally only extend the bow Outrigger and do the bow-first load. Lift the bow onto the Outrigger, lift the stern into the stern block, then lift the bow sideways off the Outrigger into the foam block.
You can fiddle the boat forward and backward, but that may knock the blocks over and you'll have to re-position them by lifting the hull an inch again. With practice, it goes fast. I have to use a 3 or 4 step ladder on my high van, but I have to do that with that vehicle no matter how I'm affixing kayaks or canoes.
You could prevent the blocks from rotating or moving by taping them to the bars, but I don't do that because I don't want to drive around with foam blocks on my vehicle. Nor do I want semi-permanent yak saddles on my vehicle, which is why I much prefer easily removable foam blocks.
I should point out that if you have a very peaked front deck and short bar spacing, you may not be able to carve enough depth into standard commercial foam blocks, but you can always make your own from minicell.
Here's a picture of my van with a 17'-2" Surge seakayak in the middle and a 22'-3" Huki outrigger on the side, both supported on standard foam blocks with minor carving of the bow blocks. To get the kayak in the middle, I have to do it with one of the side boats removed. I just lift it (36 lbs.) onto the bar, and then crab-walk it to the middle where the foam blocks are. All using the step ladder for reach.