-- Last Updated: Aug-05-13 12:29 AM EST --
The trick to loading a heavy boat is to use a method that doesn't require you to lift so much weight overhead. There are three easy ways to do this, and all require a rack that lets you start the loading process by leaning the boat against the rack (presumably you know how to get yourself under the boat and carry it on your shoulders, because if you haven't mastered that you're in for all kinds of difficulty no matter what method you use).
The first option is to have the rear cross bar mounted close enough to the back end of your vehicle that you can lean the canoe against that cross bar. Second, you can install lengthwise bars which connect the ends of your existing cross bars. Third, you can use a rack extension, so that one cross bar extends a few feet out for temporary use when loading.
With any of these, you simply walk up to the car with the boat on your shoulders and the front end higher than the rack. Set the boat down so that the front end is on one of those loading-aid bars described above and the other end sits on the ground, and walk out from beneath it. Go pick up the end that's on the ground and slide the boat up onto the roof. For the first bit of the loading process, you'll be lifting a little less than half the weight of the boat, which is a lot, but since you're only lifting it waist high, it's easy. As you push it farther onto the rack, "your end" just keeps getting lighter and lighter, so that by the time it finally becomes necessary to lift your end higher than your head, you are only lifting a tiny fraction of the overall weight, and immediately after that you end up just sliding the boat and not lifting anything at all.
I just cringe every time I see people struggle with overhead lifting of such a heavy boat as yours. You loading system "sort of " addresses that problem but you still end up needing to lifft half the boat's weight over your head, and with a boat that heavy, that's asking a lot. I've posted about this many times here over the years, and recently gave the example of how as a scrawny teenager weighing about 135 pounds I had no trouble at all loading an aluminum Jon boat on top of a full-size van. It was a little tricky working myself under the boat to get it onto my shoulders for carrying to and from the water (I walked my hands along the floor of the boat with one end up and the other end resting on the ground, ending up where I could place the floor of the boat across my shoulders and balance it there (the center "V" in the floor was place for my spine, but using a boat cushion worked well too), but the loading part was very easy.
With both the side-bar loading method and the extension-bar method, you'll be doing some shuffling of the boat's position during the loading process, but that really doesn't make things any more difficult as far as muscle exertion goes. It only means that that it takes a bit more attention to detail. Slide-on loading directly from the rear can be done without even watching what you are doing.