As a rule of thumb, if you can grab the bow or stern of the kayak, and move it up or down, and see the roof flex (like I can with my Thule racks mounted in my Explorer's factory tracks) I'd go for bow and stern lines. They take a lot of the dynamic load off the roof sheet metal and transfer it to the frame. Besides, it's safer, I've had one of the front inside saddles shift towards the center of the cross bar at 65 mph, and I was real glad I had the b/s lines. Along this train of thought, has anyone ever drilled a small hole through the saddle mounting flange that straddles the cross bar and the cross bar itself, and then run a bolt through both so this won't happen? FYI, Thule has a square cross sectional profile cross bar. John Blackburn Steve Scherrer wrote: > AdrianNEFF_at_aol.com writes: > Do you think bow and stern lines are > always necessary, or only with less secure racks? > > It's your call but........like a safety chain on a trailer, the b/s lines > make the connection *bombproof*. period. > > we have a rule at the shop that ALL commercial loads <rental, trips and > tours,etc.> require b/s lines. > > steve > > *************************************************************************** > PaddleWise Paddling Mailing List - Any opinions or suggestions expressed > here are solely those of the writer(s). You must assume the entire > responsibility for reliance upon them. All postings copyright the author. > Submissions: PaddleWise_at_PaddleWise.net > Subscriptions: PaddleWise-request_at_PaddleWise.net > Website: http://www.paddlewise.net/ > *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Hi David, thanks for the reply. I've thought about this a lot, and IMO the Thule bars are sized for much greater loads than two fiberglass kayaks. It'll support me when I put the two ends of the crossbar on bricks. So I'm not too worried about weakening the structure. Since the bar is being bent upwards due to the lift created by the hull moving through the air because the hull is secured to the crossbar, the upper surface of the bar is in tension, the lower edge is in compression and the center of the bar is not stressed. So drilling a small hole through the bar at the centerline shouldn't cause too much diminution of the structural strength. Although a couple of hose clamps might work, I think that they could also be moved sideways without too much force being used. The surface of the bar is smooth so even though the hose clamp is tight, it'll slide. I wish I had a way to tighten the saddles more than what I can using my hand. Any other Thule users/dealers out there that want to weigh in on this discussion? David Christianson wrote: > John, > > I have worked on avionics and air frame mechanics have very hard > rules. One is never to drill a hole in any structural member. It weakens > the whole structure - unpredictably. I would suggest putting a hose clamp > at the point you would drill a hole. > *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
John, I have worked on avionics and air frame mechanics have very hard rules. One is never to drill a hole in any structural member. It weakens the whole structure - unpredictably. I would suggest putting a hose clamp at the point you would drill a hole. Dave Christianson At 02:57 PM 12/13/2001 -0800, you wrote: >I've had one of the front inside saddles shift towards the >center of the cross bar at 65 mph, and I was real glad I had the b/s lines. > >Along this train of thought, has anyone ever drilled a small hole through the >saddle mounting flange that straddles the cross bar and the cross bar itself, >and then run a bolt through both so this won't happen? FYI, Thule has a >square >cross sectional profile cross bar. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
From: "David Christianson" <davchris_at_skypoint.com> > I have worked on avionics and air frame mechanics have very hard > rules. One is never to drill a hole in any structural member. It weakens > the whole structure - unpredictably. I would suggest putting a hose clamp > at the point you would drill a hole. I'll offer a different opinion (my undergrad thesis was on holes in structural steel beams - published results in ASCE journal). The following comments apply to steel crossbars in rectangular or circular cross section. All bets are off with factory crossbars of aluminum or other materials and strange shapes. You can safely drill horizontal holes under certain conditions. As long as you're not too near points of high shear (i.e. near the towers on a rack) and are not near points of high tension (i.e. near the top- or bottom-most part of the crossbar) a hole doesn't have a big effect. There are other issues related to how thin a material is, but all crossbars I've seen are relatively thick. Therefore, a hole placed near the mid-span of the crossbar, right on the horizontal centerline of the bar shouldn't affect it too much. Keep the hole small - I wouldn't go much over 1/8", maybe 3/16 in a crunch. A vertical hole is even less of a risk, since lateral loads are likely less than vertical. This is more so with the wide Thule bars, less with the circular section Yakima bars. A solution that doesn't involve holes is always better. Mike PS Airframe mechanics do drill-stop cracks in aircraft components. This is the one time you would prefer a drilled hole. There are limits on how this can be done, however. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Just out of curiosity Mike, would a flanged, tight fitting mechanical fastener (nut, bolt, and washers/ or rivet) transfer the stress as if it weren't drilled? My conjecture is that these general rules would be far different for a solid material as opposed to tubing as tubing relies on continuous surface runs for strength. Is this true? Michael Daly wrote: > > Therefore, a hole placed near the mid-span of the crossbar, right on the > horizontal centerline of the bar shouldn't affect it too much. Keep the hole > small - I wouldn't go much over 1/8", maybe 3/16 in a crunch. > > A vertical hole is even less of a risk, since lateral loads are likely less than > vertical. This is more so with the wide Thule bars, less with the circular section > Yakima bars. > > A solution that doesn't involve holes is always better. > > Mike > > PS Airframe mechanics do drill-stop cracks in aircraft components. This is the > one time you would prefer a drilled hole. There are limits on how this can be done, > however. -- ¤ Gabriel L Romeu ¤ http://studiofurniture.com + /diary or + /paint *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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