roof rack
I strapped two 70" 2x4 s to the factory rack with cam buckle cargo straps. The 2x4s need to be kept close as possible to the feet of the factory rack. I used the factory cross bars p;ushed up tight to the wood. I bolted a wood block in the center of each 2x4 to keep the boats from rubbing in the middle. My son has those 2x4s on his car now. I started them in 1976 and used them on about four different outfits over the years. Look for white, soft, stud grade lumber with small knots. The soft wood is kind too ash rail and thin aluminum as well. Always tie down both ends of the canoes so the rack never has to handle any uplift.
tying down
+1000
I look at it this way - a rack is designed to keep stuff off your car; tying it down is what keeps it on the car.
All factory racks
are not equal. Some are more for show than function - reportedly, the worst are attached with sheet metal screws. In a previous thread on this same subject several people told horror stories about the rack coming right off the car, boat(s) and all. If you are using a factory rack as the base for hauling boats fore and aft tie downs are probably more important than they were in the old days when we clamped the racks to the rain gutters.
Peter
2x4s
if I had a vehicle with a factory roof rack on it, I’d just cobble together my own canoe rack using 2x4s
as someone said above, screw a block in the middle wide enough to keep the two canoes seperated so they don’t rub together. I’d likely add small blocks on the bottom, positioned on both sides of the rail of the factory rack (i.e. inside and outside, on both passenger and driver’s sides) to prevent the 2x4s from sliding sideways - U bolt clamps to hold the wood to the rails.
I’d never trus a factory roof rack completely - useing bow and stern tie downs helps hold the roof rack to the roof as well as holding the canoes to the rack - along with straps over the hulls
the only real advantage for a Yakima or Thule rack is they generally going to be quicker to put on and take off than a 2x4 rig - Yakima or Thule racks with seperate towers (rather than using the factory roof rack) would likely be a stronger setup.
the obvious disadvantage to Yakima/Thule etal is the cost, which can easily run to several hundred dollars, depending on what you buy
I don’t have a vehicle with factory roof rack - so I use a Yakima rack system for my Dodge Dakota, and a Quick n’ Easy rack for my F-150. both work well