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From: Ken Cooperstein <cprstn54_at_att.net>
subject: [Paddlewise] Wind forces on roof mounted kayaks
Date: Thu, 23 Apr 1998 17:49:55 -0400
In addition to strapping the yak to the rack in the vicinity of the
saddles on my Thule, and a bow and stern line to the toggles, I also use
a simple "spring" line to the bow and stern that really locks the yak in
position.

I make a small bowline (the knot) before attaching the bow and stern
lines and loop it over the bow or stern.  I make the bight (loop) big
enough to slide back about 8" on the bow or stern, but no more.  I then
run the standing part straight fore-aft and taut to my factory rack (on
which the Thules are mounted).  For slippery polyethylene yaks in
slippery plastic saddles, this does the job.  If I didn't have the
sturdy factory rack as a tie down, and didn't trust the Thules for
fore-aft strength, I would run these spring lines over the roof, down to
the bumper.

Ken


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From: SG Scorpio <SGScorpio_at_aol.com>
subject: Re: [Paddlewise] Wind forces on roof mounted kayaks
Date: Tue, 21 Apr 1998 12:04:02 EDT
hlevin_at_jlc.net (Hal Levine) wrote on April 21:
>>I was hoping for some good input on what dynamic forces are really
working on the kayaks on the roof of my car.

There must be some engineering types out there that can calculate the
drag, lift etc. for kayaks moving through air.  I started thinking about
this when I saw someone traveling with a mattress on the roof of their
car.  Although is was tied on to the roof, at 55 it was NOT touching the
car at all!

My SUV has a notice that the "maximum load is 50 lbs. distributed
evenly" but my view is that at highway speeds (over 55mph) there may be
a stronger backward and lift vector working on my boats.  I travel with
the boats upright in saddles and it seems that a 50 to 70+ mph wind will
attempt to lift the boats out of the saddles and push them backward
possibly eliminating any downward force on the front saddles.

P.S.  I estimate that I may have traveled over 10,000 miles with my
boats on the roof and they have made it to all my destinations!

    Hal >>


IMHO the religious use of strong bow *and* stern lines, tied securly to anchor
points on the bumpers are a good idea.  If the lines are *bombproof* the only
purpose of the rack is to keep the boats off the top of the vehicle.  The
lines double as bow lines on the boats when I get to put-in.  In the 20+ years
of paddling I have yet to loose a boat off the top of a rig.<knocking on wood>
In the 13 years of  working in a paddle shop I have heard of many cartopping
incidents, all of which were a result of *not* using proper bow and stern
lines.
As far as resistance goes, I know I get *way* better gas mile sans kayak.
Steve Scherrer
President ACKS

Alder Creek Kayak and Canoe
250 NE Tomahawk Island Dr.
Portland, Oregon   97217

Web:  http://www.aldercreek.com
Email: aldercreek_at_aldercreek.com
Phone: 503-285-0464
Fax: 503-285-0106
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From: Kirk Olsen <kolsen_at_imagelan.com>
subject: Re: [Paddlewise] Wind forces on roof mounted kayaks
Date: Wed, 22 Apr 1998 11:56:18 -0400 (EDT)
From: Bill Leonhardt <leonhardt_at_bnldag.ags.bnl.gov>

>At 08:23 PM 4/21/98 -0700, someone previously wrote:
>>It's good to remember that if you tie your boat to your racks, that's
>>only as good as how well your racks are attached to your car. 

Having watched a roof rack with the car's cheesy gutters still attached
fly off the car, with a sheet of plywood, I agree...

> I always use bow and stern lines tied directly to my vehicle and would
> encourage everyone to do the same.  

Could you explain to me why you use lines to the back of the vehicle?  I 
almost always use 2 lines to the front of the car, but don't bother with any 
lines to the back.


A paddling acquaintance doesn't normally tie down his boats UNLESS he's
going to exceed 25 mph.  It's rather disconcerting to ride with him after
just tossing a couple of boats onto the roof rack.  Even moving my car
around in a parking lot I want at least one tie down strap.

kirk
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From: Rich Kulawiec <rsk_at_gsp.org>
subject: Re: [Paddlewise] Wind forces on roof mounted kayaks
Date: Wed, 22 Apr 1998 13:11:58 -0400
On Wed, Apr 22, 1998 at 11:56:18AM -0400, Kirk Olsen wrote:
> Could you explain to me why you use lines to the back of the vehicle?  I 
> almost always use 2 lines to the front of the car, but don't bother with any 
> lines to the back.

'Cause if you wind up hitting the brakes *really* hard, or unfortunately,
getting into a front-end accident that stops your car abruptly, then the
boats on your roof are going to continue moving forward...

---Rsk
Rich Kulawiec
rsk_at_gsp.org
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From: Mark Zen <canoeist_at_netbox.com>
subject: Re: [Paddlewise] Wind forces on roof mounted kayaks
Date: Wed, 22 Apr 1998 10:46:03 -0400 (EDT)
On Wed, 22 Apr 1998, Kirk Olsen wrote:

>>From: Bill Leonhardt <leonhardt_at_bnldag.ags.bnl.gov>
>>
>>>At 08:23 PM 4/21/98 -0700, someone previously wrote:
>>>>It's good to remember that if you tie your boat to your racks, that's
>>>>only as good as how well your racks are attached to your car. 
>>
>>Having watched a roof rack with the car's cheesy gutters still attached
>>fly off the car, with a sheet of plywood, I agree...
>>
>>> I always use bow and stern lines tied directly to my vehicle and would
>>> encourage everyone to do the same.  
>>
>>Could you explain to me why you use lines to the back of the vehicle?  I 
>>almost always use 2 lines to the front of the car, but don't bother with any 
>>lines to the back.

fast stops... what will keep your boat from flying forward in a quick
stop??

>>A paddling acquaintance doesn't normally tie down his boats UNLESS he's
>>going to exceed 25 mph.  It's rather disconcerting to ride with him after
>>just tossing a couple of boats onto the roof rack.  Even moving my car
>>around in a parking lot I want at least one tie down strap.
>>
>>kirk

i tie my boats with 2 straps around the body, and a bow and stern line
most all the time...

mark


#------canoeist[at]netbox[dot]com----http://www.diac.com/~zen/mark-----
#
mark zen                      o,    o__              o_/|   o_.
po box 474                   </     [\/              [\_|   [\_\
ft. lupton, co 80621-0474 (`-/-------/----')      (`----|-------\-')
#~~~~~~~~~~~~~~~~~~~~~~~~~~~_at_~~~~~~~_at_~~~~~~~~~~~~~~~~~~~_at_~~~~~~~~_at_~~~~~
http://www.diac.com/~zen/paddler  [index to club websites i administer]

Rocky Mtn Sea Kayak Club, Colorado River Flows, Poudre Paddlers
The Colorado Paddlers' Resource, Rocky Mtn Canoe Club Trip Page 
--
Majority, n.:
	That quality that distinguishes a crime from a law.
Positive, adj.:
	Mistaken at the top of one's voice.
		-- Ambrose Bierce, "The Devil's Dictionary"


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From: Kirk Olsen <kolsen_at_imagelan.com>
subject: Re: [Paddlewise] Wind forces on roof mounted kayaks
Date: Wed, 22 Apr 1998 14:41:41 -0400 (EDT)
On Wed, 22 Apr 1998, Mark Zen wrote:

> On Wed, 22 Apr 1998, Kirk Olsen wrote:
> >>Could you explain to me why you use lines to the back of the vehicle?  I 
> >>almost always use 2 lines to the front of the car, but don't bother with any 
> >>lines to the back.
> 
> fast stops... what will keep your boat from flying forward in a quick
> stop??

The canoes I usually carry are 18.5 foot long marathon flatwater racing 
boats.  These boats overhang the back of the car by several feet.  The
overhang at the back is slightly more than the distance from the front tie
downs to the bumper.  I decided to stop using a rear rope after 
noticing that the front ropes would retension before the rear ropes would, 
even in the case of a boat launching forward.

> i tie my boats with 2 straps around the body, and a bow and stern line
> most all the time...

I use 2 straps, each doubled over, around the body of the boat, then one line
to each side of the front bumper of the vehicle.  With my singles canoe
I also like to use a foam pad on the roof rack so that the gunwales sink
into the foam when I tension the straps.  This has really cut down on
the amount the boat wiggles when encountering crosswinds or trucks.  The
singles canoe has extreme tumblehome so the straps are about 5 inches from
the gunwales where they attach to the rack.  This gap prevents the straps
from holding the gunwales in place when the boat tries to shift.

kirk
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From: Bill Leonhardt <leonhardt_at_bnldag.ags.bnl.gov>
subject: Re: [Paddlewise] Wind forces on roof mounted kayaks
Date: Wed, 22 Apr 1998 13:59:34 -0400
At 11:56 AM 4/22/98 -0400, you wrote:
>
>Could you explain to me why you use lines to the back of the vehicle?  I 
>almost always use 2 lines to the front of the car, but don't bother with any 
>lines to the back.
>
>
>kirk
>***************************************************************************
Kirk,

If you tie a boat with two lines to the bow and I tie with one line to the
stern and one to the bow we have the same number of lines and tiedown
strength, assuming we use the same material.  My feeling is that they would
perform the same if the vehicle didn't move.

Now let's talk about probable failure scenarios.  I expect the bow (and
stern) line to be needed when the saddles alone no longer hold the boat.
This can happen:

	1.  When I'm driving really fast.
	2.  When I'm driving sorta fast and more wind comes from nature and/or
		a passing vehicle.
	3.  When I have to make a PANIC stop!!

So, sometimes the boat wants to slide forward and sometimes aft.  The
length of my bow and stern lines is unequal, as is the angle they make to
the ground so that I know only one will be stopping the slide initially.  I
expect that a single line has that strength (and, I hope, so does the
attachment on the boat).  The second line is therefore a backup.

With your scheme, even if you use two independent lines at the bow, I would
expect you to use the same attach point on the boat.  So all your holding
power is from one attach point.

My way does have a down side.  I carry my kayaks on the roof of a Dodge
Caravan.  The bow lines travel aft from the front bumper to the bow(s) so
they are over the hood.  The stern lines travel aft from the rear bumper to
the sterns thus allowing people in mall parking lots to walk into them.  I
generally hang a flag from one stern and truthfully this hasn't happened
yet, but I think it's possible.

I think that there's more than one way to tie down boats and the important
thing is that we use a method that works reliably.

Bill
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