I've always wondered about this myself since I center it on the length of the truck so when I'm going up trails a bunch of canoe isn't hanging off the back (17' Mad River). With the large front overhang the front straps are key for highways speeds.
This photo is at Diamond Lake, OR. The canoe is strapped down (black straps) and then the stand up paddle board is strapped to the canoe (blue straps). The front and rear of the canoe have red ratchet straps so I can fine tune the tension. This was about 200 miles round trip.
Yakima racks held fine but flex around more than i'd like if I were to do a really long haul.
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