strengthening roof racks

Hi guys, was wondering if anyone has a good idea on how to reinforce factory roof racks. My mountaineer has plastic posts and I am worried that it won't support two kayaks. I'm pretty sure max weight is around 100 ib, I'll be carrying a revo 13 on thule cross bars/Hullivators and a eddy line c14. Was thinking about placing wood blocks under the racks? Here is a pic of my suv factory rack.
Thanks

just got these thugs, but primarily concerned with the factory plastic rails?note: my suv factory rails are the image in my first post.I just got the thule rack system that clamps on. Rei said they're the only ones that fit my car.

That the components on the vehicle are plastic might not be a cause for concern as they may well have sufficient capacity to support the load you are looking to carry. I would start with the manufacturer's ratings and guidelines which should be listed in the owner's manual.

The load bearing capacity should be sufficient for what you have described IMO, their rating numbers have to take in consideration the wind shear/lift scenario as well.

That the components on the vehicle are plastic might not be a cause for concern as they may well have sufficient capacity to support the load you are looking to carry. I would start with the manufacturer's ratings and guidelines which should be listed in the owner's manual.

The load bearing capacity should be sufficient for what you have described IMO, their rating numbers have to take in consideration the wind shear/lift scenario as well.

Thanks, the rails just look so flimsy. Thin Plastic. Do you know if the car manufacturers rate the load bearing modestly with room to play with?
max   for my 2000 mountaineer roof rack is 165LBs hope ill be ok!?

Tie down the bow and stern of each kayak. It will reduce the upward stress on the racks.

Tie down the bow and stern of each kayak. It will reduce the upward stress on the racks.

Esto.....and stick your arm out the window and hold onto your yak as you would a mattress 

Tie down the bow and stern of each kayak. It will reduce the upward stress on the racks.

Esto.....and stick your arm out the window and hold onto your yak as you would a mattress 

Have you done that??? Naw, I wouldn't think so.

That the components on the vehicle are plastic might not be a cause for concern as they may well have sufficient capacity to support the load you are looking to carry. I would start with the manufacturer's ratings and guidelines which should be listed in the owner's manual.

The load bearing capacity should be sufficient for what you have described IMO, their rating numbers have to take in consideration the wind shear/lift scenario as well.

Thanks, the rails just look so flimsy. Thin Plastic. Do you know if the car manufacturers rate the load bearing modestly with room to play with?
max   for my 2000 mountaineer roof rack is 165LBs hope ill be ok!?

I would presume there is a safety factor multiplier to that capacity rating. If it's listed as being 165 pounds and you are at about 100, it should be fine. Good advice from Mike about securing bow and stern! Try to orient them nicely parellel (not sideways to vehicle centerline) to minimize drag.

Tie down the bow and stern of each kayak. It will reduce the upward stress on the racks.

Esto.....and stick your arm out the window and hold onto your yak as you would a mattress 

Have you done that??? Naw, I wouldn't think so.

Sometimes I think that should be Cabeza de Piedras... Funny though!   

Tie down the bow and stern of each kayak. It will reduce the upward stress on the racks.

Esto.....and stick your arm out the window and hold onto your yak as you would a mattress 

Have you done that??? Naw, I wouldn't think so.

Sometimes I think that should be Cabeza de Piedras... Funny though!   

I know you've seen those fucking idiots on the freeway 

Tie down the bow and stern of each kayak. It will reduce the upward stress on the racks.

Esto.....and stick your arm out the window and hold onto your yak as you would a mattress 

This! Not only will you have a stronger roof rack, but you'll have a stronger arm too.