best method to tie down a sheet of plywood?

[Guy]

I am scheduled to teach knotting to scout leaders next week.  I want to present practical scenarios.  I really don't have any idea what the best method is to tie a sheet of plywood to a carf roof rack.  Ideas?

[SS369]

Hello Guy and welcome.

The answer(s) to your question can depend on a few things. The type and configuration of the roof rack. The type of rope you dare use and the necessary amount available.
First I would like to say that in this endeavor, security of the rack is first, the tying of the sheet goods is without failure and the speed, if you even do this, at which you transport it is slow.

Some roof racks have two rails running front to back, some have additional cross bars from side rail to side rail. This can make a difference in the securing by rope.

Which ever it is you will have to make sure to bring the edges downward towards the ground to attempt to maintain integrity of the tying as well as limiting the wind's attempt to use the sheet(s) as a wing.

The tying of it should include some means of well fixed rope at each corner that tensions to the rack equally. Added wraps down the centers and around the rack would add a bit of unifying the loaded sheets and further take some more of the stresses to be seen.

I know it will be done and has been, but I caution, rethink this. (Borrow a trailer or truck)

SS

[Benboncan]

Which ever it is you will have to make sure to bring the edges downward towards the ground to attempt to maintain integrity of the tying as well as limiting the wind's attempt to use the sheet(s) as a wing.

I am afraid that this is bad advice , what you just described is close to an airfoil section

http://en.wikipedia.org/wiki/Airfoil

It will actually encourage lift even at zero angle of attack.

[SS369]

Perhaps what I wrote is wrong Benboncan, I didn't think so with the roof and car underneath creating too large an air disturbance to allow for the pressure differential. I believe the laminar flow would not be sufficiently different enough to require a pilot"s license. ;-)
Wings that have the same front and rear configurations don't do well.

"I am afraid that this is bad advice , what you just described is close to an airfoil section"
Close to an airfoil section, but not quite an airfoil.

But, I'll retract the word wing all the same.

Instead, bring the edges down to load the sheet well so the wind will have a harder time attempting to make a sail out of it.
Any better?

Regardless the rest stands.

SS

[Andy]

Greetings everyone!

It's been way too long since my last visit to the forum. I hope you all are in good health and enjoying at least some of your time on planet Earth.
Somewhere between extended camping trips and shifting towns, the time I used to spend reading posts on the forum has disappeared, and I have been hoping for a spare hour to come see what is happening.
Wow... By the number of recent posts, it looks like the forum has been amazingly active! Lots to learn in those threads, I am sure.

I reply to this particular thread because in the past months, I have several times needed to carry doors or plywood on my ute's roof rack. (For those of you in the northern hemisphere, a "ute" is short for "utility vehicle" in Australia and New Zealand, and stands for something like a pick-up truck.) On those occasions, whatever knots I came up with left me unsatisfied. I have been meaning to look in Ashley, but, lo and behold, someone already started a thread on the same topic!

When I have a chance I'll post a picture of my roofrack. In the meantime, here is a diagram. The "|" lines represent the two bars across the roof. The "x" represent anchor points, around which the rope can be turned. I have given them a number for convenience.


  |                                 |
  x1                                x2
  |                                 |
  |   ( <-- length of car --> )     |
  |                                 |
  x3                                x4
  |                                 |
 


Looking forward to being in touch again.
Wishing you all a beautiful weekend,

Andy

[knot4u]

I'll describe here what I would do.  I'm NOT recommending it because I've never actually done it this way.  So, if it doesn't work for you, DON'T BLAME ME.

Basically, I'd make a ramp out of the plywood.  I'd put something on the rear such that the plywood lies upward taller in the back.  That something could be blocks of wood, stacks of clothing, or whatever.  Use your imagination.  Just make sure it's a ramp, with the front of the plywood flush with the front windshield, preferably.  Then, I'd cinch down the whole thing by using two or more Trucker Hitches.

Here's why I think this idea would work:  I have a similar device connected to the front of my ski rack on top of my SUV.

EDIT:

Anchor points would definitely include the front and back bumpers.  I'd run two or more ropes from the front bumper to the rear bumper.  I'd still carry out the idea I posted above.  The ropes running front to rear would help prevent the board from flying away even if a gust of wind gets underneath.

[Andy]

Hi Knot4u!

Your ramp probably makes sense from an aerodynamic standpoint, although I'm no expert.
I'm going through town at low speeds, but it's quite hilly, and I'm more concerned about securing the cargo than in having it take off.
The difficulty with truckies to tie down doors to the roof rack is that the doors are quite slim (flat) and may have a tendency to slip.
It's easy to tie a mattress or a sofa on the rack with truckies because there is height for the truckie to pull down on. Not so with a nearly flat door.
I am modifying the diagram to show where the corners c1, c2, c3 and c4 might lie in relation to the anchor points x1, x2, x3 and x4.
Of course the door could be positioned so that c1 is closer to x1. But then c3 is further from x3. Does this give you a taste for the task?


     |                                 |
     x1                                x2
     |                                 |
c1---|---------------------------------|---c2
|    |                                 |    |
|    |   ( <-- length of car --> )     |    |
|    |                                 |    |
c3---|---------------------------------|---c4
     |                                 |
     x3                                x4
     |                                 |


Wishing you a beautiful day,

Andy

[knot4u]

I edited my post above.
http://igkt.net/sm/index.php?topic=2817.msg17264#msg17264

By the way, Andy, I don't quite understand your individual issues.  It seems like you're saying you having a problem with finding suitable anchor points.  With long enough rope, there's always somewhere to anchor the rope to a car.  The anchor points don't have to be at the locations you've shown.

[Andy]

Hi Knot4u,

Good point. If you're not using the x1-x4 anchor points, the truckie works. Maybe I'll go in that direction next time.
I still have a feeling that there is an elegant solution through x1-x4 lurking somewhere, perhaps pulling on the corners of the door. And I have a feeling that this is something a sailing person would know about. I'll flip through Ashley soon enough.

Regards,

Andy

[SS369]

Hello Andy,

it seems that you've gone from needing a way to tie down a sheet of plywood - 4ft x 8ft, to requesting help for a door that at most likely is 3ft x 80 inches. Different enough to require other procedures for securing.
With the sheet plywood, the anchor points would most likely be under the sheet at least a few inches, but in your diagram the item (door) is much narrower than the anchor points.

I took a stab at a diagram for you to consider. I'm sure there are many others. I hope it gives you something to work from. Since you have indicated this is to be a door and that you'll travel slow and easy, I feel this will be secure up and down hills and curves barring any undo outside influences.
You potentially could wrap a sheet of plywood similarly, but that is entirely up to you.

All runs of the rope should be cinched as tight as possible throughout the tying and the frapping in the center crossing should tighten it further.

[Andy]

Hello SS369,

Thank you for your message and taking the time to make and upload that detailed diagram with commentary!

it seems that you've gone from needing a way to tie down a sheet of plywood

Guy's original post was about plywood, I hijacked it to also discuss doors:

I reply to this particular thread because in the past months, I have several times needed to carry doors or plywood

I like your ideas, I'll see if I have enough rope next time I transport a rope, if not I'm sure there will be a variation that works over a short distance.

Warmest wishes,

Andy

[SS369]

G'day Andy,

I did read this> Quote: "I have several times needed to carry doors or plywood on my ute's roof rack."

Sorry that I specified you, but I got caught up in it all. ;-)
Be careful when you hijack! lol

If you don't have enough rope to insure the safety of your door/plywood then you could fail at transport it.
Decent rope is cheap and more is better. :-))

Regards,

SS

[Dan_Lehman]

This general problem is in need of specifics,
and it seems that the OP --lastest post 10feb-- is not going to be
giving them; but he asked about the general case, anyway, as a
*rope problem* for illustration in training.  And it could be that!

I surmise that such problems are regularly attended to at places
that sell such materials, and I'm thinking that they have available
only some synthetic twine, not rope!?  Anyone have experience
with buying plywood and having it tied to a rood (rack or not) ?!

My guess is that the airfoil issue is not of practical concern, but
maybe there's a split in cases between highway (50mph +) transport
and more local-travel, slower transport.

If there is a roof rack with cross-bars that extend beyond the width
of the plywood, I'd like to tie across the tops of them fore & aft,
and tighten that tying by anchoring a length-wise-oriented line
in the center and running it over the fore end down to a bumper;
conceivably, this line could pull on & tighten both cross-lines.
Then maybe run the same line (or attach another) back over the
aft end, to rear bumper.  Some bending tension is probably best
so as to keep the board from *flapping* with air pressure.

Webbing would be good to have going around the hard edges
of the board.


--dl*
====

[Andy]

Hi SS369, hi Dan!

SS, thanks for your thoughts about safety!

Dan, it's a treat to hear your voice again. Thank you for presenting this simple and effective solution.

Warmest wishes from NZ summertime,

Andy

[skyout]

I surmise that such problems are regularly attended to at places
that sell such materials, and I'm thinking that they have available
only some synthetic twine, not rope!?  Anyone have experience
with buying plywood and having it tied to a rood (rack or not) ?!

A quick google search showed this. LOL