Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4814104.
Side support for Canadian canoe on car roof bars much like the Thule ones you can buy. These slide into the T slot in the bars and clamp down with a M6 25mm socket cap bolt with the nut heat set into the base. It has slots either side for the straps to go through and loop under the bar to firmly hold in place ensuring no side to side movement. I printed these in a printed chamber on its side with supports in ABS and they are rock solid once clamped in place. There isn't much force placed on these by the canoe as they just retain the straps and stop side movement, but please ensure you print is strong and your canoe is safely strapped on, use at your own risk.
The base is shaped to for Vauxhall/Opel aero style bars but would be fairly easy to modify for any other bar profile with a T slot.
Print two per bar one either side adjust to the width of your canoe and clamp in place.