Re: [Paddlewise] Bow and Stern Lines

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.

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