So in all the conversations about ways to carry your kayak on roof racks and how to get it up there and back off, I’ve literally never seen anyone do what I’ve been doing for years. So I figured I’d show everyone. It works incredibly well for me, and is actually a lot easier than it looks (for me).
NOTE: I am in no way implying nor suggesting that…
a) everyone should do it this way
b) it’s the best way
c) it’s easy for anyone (it isn’t)
d) that it won’t result in injury to you (I’ve never been injured doing it, but don’t blame me if you try it and throw your back out)
I’m only saying it works well for me—nothing more.
I carry my kayaks on J-Hooks because the side of the boat is its strongest area, and carrying your boat on its side means less damage or oilcanning to your hull.
Basically, to get the boat up, I use a kind of clean-and-jerk technique —but I’m not a weightlifter, and if someone criticizes my technique and says it has nothing to do with actual clean-and-jerk technique…I’d reply “That’s fine, I never said it was accurate clean-and-jerk technique, just vaguely similar to it, and it works well for me.” 
The key to lifting the boat (again, for me) is that after picking the boat up off the ground, I forcefully straighten my back which provides leverage and power to swing my arms and the boat up over my head in one smooth motion. (You can’t do this slowly, or you’ll be in trouble. You MUST do it in one swift, smooth motion.) Once the boat is over your head and you’re under it, holding it up there really isn’t difficult (for me). Then I just take a step forward and drop the boat into the J-Hooks. Done!
To get the boat back down, I simply slide it out of the J-Hooks to the rear of the vehicle. The key here is I get my arm straight up to grab the cockpit rim on top as the boat slides down off the car. Then I just let the cockpit rim settle onto my shoulder, where I can comfortable carry it as far as needed to the water. For me, it’s almost effortless.
Here’s a video of loading and unloading (with some slo-mo instant replay of the lift when loading)…
This is a Wilderness Systems Tempest 170 that weighs somewhere between 55-60lbs. I’m 5’10" tall, and while I’d say I have very strong back muscles (from decades of paddling) I don’t have really strong arms (I never do upper body weight training…just tons of paddling). But this method is easy for me because of technique—not brute strength. And yes, I know all about not using your back to lift heavy objects. I’ve never injured myself doing this hundreds (thousands?) of times.
So just posting it in case the same technique might work for anyone else. Because for me, it’s great—I can load/unload my kayaks by myself with no problems…and it’s fast. I’m usually loaded and gone long before everyone else…and also the first to be in my boat in the water.
Your mileage may vary! If you want to try doing this, it might be a good idea to have a spotter or two nearby just in case. I’ve found that the key to doing it is you must commit to swinging the boat up over your head. If you commit, it can work smoothly. If you don’t commit (or hesitate while doing it) you might find a 55lb boat tumbling down on top of you.