Hal, I have never done that type of calculation. I quess it could be approximated with the hydrolics programs on the market if viscosity is a input variable. However I have noticed more of a problem with twisting moments when passing or being passed by trucks or in cross winds. This force concerned me more than the wind drag from the forward motion of the car. Jim >>> Hal Levine <hlevin_at_jlc.net> 04/21/98 01:13pm >>> 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 Wilton, NH Power your boat with carbohydrates, not hydrocarbons. http://www.jlc.net/~hlevin 0 \_O \============\==============/ ^^^^^^^^^^^^^^^^^^ \^^^^^^^^^^^^^^^^^ 0 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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. I like to put a bow line on for highway trips as cheap insurance. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
At 08:23 PM 4/21/98 -0700, you 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. I like to >put a bow line on for highway trips as cheap insurance. >*************************************************************************** > Dear List, I always use bow and stern lines tied directly to my vehicle and would encourage everyone to do the same. Just a word of caution, though. I have two older boats, polyethylene, with bow and stern grab loops which is where I tie the bow and stern to the vehicle. These grab loops are held by a plastic clamp block screwed into the boat. Since I have had occasion to remove these screws, I am now aware that the screw threads in the boat appear to be merely nuts that were inserted (probably hot) into the deck. What I'm trying to illustrate is that some grab loop attachments are not all that strongly attached to the boat and, even though you are tying these, say to your bumper, you may not be securing the boat as well as you think. Still, this is still better than not tying the bow and stern at all. The bottom line is..... Secure the boat well, both in the saddles and at the bow and stern attachments. I hope this doesn't sound too preachy, it's just that, well, maybe I may be driving behind you some day. Bill Leonhardt *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
On Apr 22, 10:24am, Bill Leonhardt wrote: >I have two older boats, polyethylene, with bow and stern grab loops which >is where I tie the bow and stern to the vehicle. These grab loops are held >by a plastic clamp block screwed into the boat. Since I have had occasion >to remove these screws, I am now aware that the screw threads in the boat >appear to be merely nuts that were inserted (probably hot) into the deck. > >What I'm trying to illustrate is that some grab loop attachments are not >all that strongly attached to the boat and, even though you are tying >these, say to your bumper, you may not be securing the boat as well as you >think. Hi all, What I do is to loop my rope around the kayak behind (for the bow, or ahead for the stern) of the hatch. This doesn't rely on the strength of the grab loops or their attachment to the hull. This also doesn't distort my kayak as much (it is plastic) since I don't have the same leverage as I would out at the ends. I suppose this doesn't help if you don't have hatches to hold the loop of rope from sliding toward the end of the boat. -- henry o_, _at_ ------------ [\/ o,/ Henry Davies (`-----/----') <-----</-----> OASIS, Inc. ~~~~~~~~_at_~~~~~~~~~~~~~~~~~~~~~~~~/~~~~~~~~~~ phone: 248.952.1490 x210 fax: 248.952.1493 email: henry_at_orion-sim.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
> I hope this doesn't sound too preachy, it's just that, well, maybe I > may be > driving behind you some day. > I've always used bow and stern lines on both kayaks and canoes. The stern line has always been to keep the boat from sliding forward when I have to slam my brakes on. The bow line has always been there just in case the rack let go and to offer some little bit of protection to those who might be near. If that did happen I would expect the boat to flap/flop back and forth to either side of my vehicle, totaling itself and doing extensive damage to my vehicle. Hopefully, the bow line would prevent the boat from flying into someone else's windshield. Moving at high speed, that would not be a nice thing. Years ago, while on a long drive for a canoe trip, I stopped for something to eat. When I came out, I happened to glance at the lines securing the canoe to the rack. Both of them were untied????? Did both of them come loose at the same time? I don't think so. So now, I try to remember to take a walk around and tug on everything to make sure they're all secure before I take off. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
On Wed, 22 Apr 1998, Sisler, Clyde wrote: [snip] >> >> Years ago, while on a long drive for a canoe trip, I stopped for >>something to eat. When I came out, I happened to glance at the lines >>securing the canoe to the rack. Both of them were untied????? Did both >>of them come loose at the same time? I don't think so. So now, I try >>to remember to take a walk around and tug on everything to make sure >>they're all secure before I take off. years ago, at a class i was attending, an top instructor was teaching. we had a break for a meal, and then came back to camp. while coming back, one of his tie downs broke. the strap around the bow, [there were no bow/stern tie downs, just around the boat and rack]. the canoe flew off the top of his vehicle at 45mph!! luckily there was nobody oncoming, or it would have been messy. the plastic dagger canoe showed barely a scratch!! i try very hard, when taking a trip with the baots, to check all tiedowns after a couple miles of driving, snug down whatever has loosened ... that has saved my butt and a boat before!! 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 -- Know what I hate most? Rhetorical questions. -- Henry N. Camp *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
In a message dated 98-04-22 14:21:47 EDT, Clyde.Sisler_at_wang.com writes: << The bow line has always been there just in case the rack let go and to offer some little bit of protection to those who might be near. If that did happen I would expect the boat to flap/flop back and forth to either side of my vehicle, totaling itself and doing extensive damage to my vehicle. >> All the reasons posted so far are excellent reasons for tying down, bow and stern. Am wondering --- and I think the first post talked to the issue --- what the aerodynamic effects of the hull do to the rack and the roof at high speeds. Have often thought about putting some sort of tensiometer in line with my bow line --- like, maybe a scale used for weighing fish? --- to see what the vertical lift measures in pounds. Crude measure, but the leverage provided to the rack from a moment arm of about seven feet might introduce a lot of stress --- strain? ... can't remember --- into the vehicle through the rack if a bow line is not used. And how 'bout the bending moments introduced into the hull? Anybody ever measured any of this? I'm gonna try if there's no data out there. (Maybe I could borrow the wind tunnel at Pax when nobody's looking!) Joq *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
At 08:12 AM 4/23/98 EDT, JCMARTIN43 wrote: >In a message dated 98-04-22 14:21:47 EDT, Clyde.Sisler_at_wang.com writes: > ><< The bow line has always been there just in case the rack let go > and to offer some little bit of protection to those who might be near. > If that did happen I would expect the boat to flap/flop back and forth > to either side of my vehicle, totaling itself and doing extensive damage > to my vehicle. >> > >All the reasons posted so far are excellent reasons for tying down, bow and >stern. Am wondering --- and I think the first post talked to the issue --- >what the aerodynamic effects of the hull do to the rack and the roof at high >speeds. Have often thought about putting some sort of tensiometer in line >with my bow line --- like, maybe a scale used for weighing fish? --- to see >what the vertical lift measures in pounds. Crude measure, but the leverage >provided to the rack from a moment arm of about seven feet might introduce a >lot of stress --- strain? ... can't remember --- into the vehicle through the >rack if a bow line is not used. And how 'bout the bending moments introduced >into the hull? Anybody ever measured any of this? I'm gonna try if there's >no data out there. (Maybe I could borrow the wind tunnel at Pax when nobody's >looking!) > >Joq I can not belive no one has mentioned this idea, DUCT TAPE! Just duct tape your kayak to you car and you will have to cut it off. For more Ideas with this miracle product visit http://intranet.ca/~mdeabreu/ducttape.html Nuff said Dana *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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