Looking at your original pictures, I think the bars are on back-to-front.
Whether this makes a material difference or not I don't know.
One thing to note is what roofbox.co.uk say on this:
"A specific watersports carrier will make carrying your gear much easier. The aim of this note is to persuade you that kayaks (or boats etc) should always, also, be tied to the carrying vehicle at both bow and stern.
Untied kayaks have, in our experience, the greatest potential for a roof bar or kayak carrier failure. The massive forces that untied kayaks can generate have even been known to snap roof bar fixing bolts with the result that a complete assembly of roof bars and kayaks has ended up on the road. We know that this has happened with almost every brand of roof bar, and regardless of whether the kayaks are on a special carrier or just strapped to the bars.
You need to fix bow and stern lines, probably using the front and rear screw-in towing eyes to get strong and accessible fixing points on the vehicle."
This text is accompanied by a picture of a kayak on a roof rack, with the bow and stern tied to the front and back of the vehicle, aswell as strapped to the rack.
I know you were carrying surfboards, but I think the principle is the same. Things like roof boxes will be designed to limit the lifting forces that might damage roof bars and racks, but water sports equipment definitely isn't, hence the problem.
I suspect the root cause of your issue was that the roof bars were not tightened sufficiently. You have sorted that by the sound of it.
I think going forward, we just have to really careful about carrying water sports equipment on a roof rack.
Pete
Whether this makes a material difference or not I don't know.
One thing to note is what roofbox.co.uk say on this:
"A specific watersports carrier will make carrying your gear much easier. The aim of this note is to persuade you that kayaks (or boats etc) should always, also, be tied to the carrying vehicle at both bow and stern.
Untied kayaks have, in our experience, the greatest potential for a roof bar or kayak carrier failure. The massive forces that untied kayaks can generate have even been known to snap roof bar fixing bolts with the result that a complete assembly of roof bars and kayaks has ended up on the road. We know that this has happened with almost every brand of roof bar, and regardless of whether the kayaks are on a special carrier or just strapped to the bars.
You need to fix bow and stern lines, probably using the front and rear screw-in towing eyes to get strong and accessible fixing points on the vehicle."
This text is accompanied by a picture of a kayak on a roof rack, with the bow and stern tied to the front and back of the vehicle, aswell as strapped to the rack.
I know you were carrying surfboards, but I think the principle is the same. Things like roof boxes will be designed to limit the lifting forces that might damage roof bars and racks, but water sports equipment definitely isn't, hence the problem.
I suspect the root cause of your issue was that the roof bars were not tightened sufficiently. You have sorted that by the sound of it.
I think going forward, we just have to really careful about carrying water sports equipment on a roof rack.
Pete
I suspect that roof rack aerodynamics are relatively unimportant on a vehicle shaped like a brick, carrying things on its roof that don’t normally fly 
I would love to know why Omtec tell us to mount them that way, but their markings are very explicit as to what goes where.
Edited to say perhaps they are quieter that way round.
Pete
I would love to know why Omtec tell us to mount them that way, but their markings are very explicit as to what goes where.
Edited to say perhaps they are quieter that way round.
Pete
Hi, I'm trying to buy the BLACK OMTEC cross bar you have been discussing in this forum.
Looking on their website looks like I found the one I'm looking for but I can't find any reputable online seller.
Where did you buy yours from?
Thanks
SKU 7522928B OMTEC Cross Bar Elegance (Black) 2 Pcs. Alu.
Looking on their website looks like I found the one I'm looking for but I can't find any reputable online seller.
Where did you buy yours from?
Thanks
SKU 7522928B OMTEC Cross Bar Elegance (Black) 2 Pcs. Alu.
I See that they all look similar and rate it at 20-40 KG max load.
Cheap knock off
Can't even find any ebay seller as nothing comes up with SKU number and brand. OMTEC
disappointing to say the least
I'll try with WV tomorrow )))
@Dig It’s definitely the thin edge trailing. The load ratings quoted are for vertical static loads, they do not take drag into account.
Drag is exponential to velocity so as an example the drag force will increase x4 for a doubling in speed, x9 for tripling the speed.....
Something has to give, why I keep a good distance from cars on motorways with giant roof loads.
Drag is exponential to velocity so as an example the drag force will increase x4 for a doubling in speed, x9 for tripling the speed.....
Something has to give, why I keep a good distance from cars on motorways with giant roof loads.
Thin edge leading, round edge trailing. Aircraft wings are designed for higher air pressure underneath in order to achieve lift off, that’s why they are round edge leading. The very opposite is required for a road vehicle which requires the higher air pressure above in order to help keep the vehicle on the road.
Bernoulli’s Principle explains this.
Just saying....
Bernoulli’s Principle explains this.
Just saying....
Its not rounded front/back or pointed back/front that of a wing that creates lift. Its the distance that the airflow has to take. The air over the top of a wing has further to flow than the air that travels below. The faster moving air creates lower air pressure than the slower moving air below, producing an upwards force on the wings. The shape of the roof bars are not affected by Bernoulli's principle at all.
Just saying...
Edit and for what its worth F1 cars 'wings' are still rounded end at the front and pointy end at the back. Just they are like aircraft wings upside down.
