# The Pro Rigger by Mike Parnell of ITI

### Rigging Training Workshop - Rigging Selection: Tension & Sling Size

Some loads can be single point picked, and the rigging is selected based on suspended weight.

Other times, a rigging task will require that we use a few steps to get to the solution. Note that in some cases the distribution of weight is required, then the sling tension is discovered as a 2-step process. In the assignment below, we can determine the sling tension in the 9.2’ leg and the 6.7’ leg by using the formula on the Master Rigger Reference Card, Panel 10 (left side of the panel).

Once we find the tension of side 1 (TS1) and then tension of side 2 (TS2), we can select the correct size of alloy chain for the lift.

In the assignment below, the ADOS stands for “Adjustable, Double (leg), Oblong (link at the top), Standard or Sling (hook at the bottom)”.

Let’s see how you do.

Determine the tension and the alloy chain sling size necessary to make the lift.

Leg 1 (9.2') Tension    =     ___________ lb
Leg 2 (6.7') Tension    =    ___________  lb
Sling Description:  ADOS    ___________"  ×  10'

Happy trails to all my crane and rigging friends,
Mike Parnell
ITI-Field Services

This is a very helpful article. if there is any software to calculate all this please send. Thanks.
Posted @ Sunday, April 24, 2011 3:09 AM by Maqbool Soomro
If CG is directly under hook, and I use L/H=Sling Tension Factor x 1/2 of load, must I also use H/L=Reduction Factor x WLL of sling to assure capacity is correct? 2 leg bridle.
Posted @ Saturday, May 21, 2011 8:56 AM by Jay Bowen
Hi Mike,
Great workshops...seeing your area of a circle rule of thumb method brings to mind outrigger load / mat spread area considerations.
Have you thought of doing a similar workshop on this topic?
I would be happy to link it / give it a mention from my webpage if you do.
Kind Regards
Mike
Posted @ Wednesday, February 29, 2012 12:12 PM by Mike
Using your numbers the math is incorrect for tension on both legs.

.3 x 14000 = 4,200
9.2/6 = 1.5333
4200 x 1.5333 = 6,439.86 or 6,440 rounded to nearest pound. Admittedly a negligible difference of only 14 lbs but nonetheless incorrect on both legs.

.7 x 14000 = 9800
6.7/6 = 1.1166
9800 x 1.1166 = 10,942.68 or 10,943 rounded up and again a difference of 33 lbs less than answer given.

I only wish I was as adroit at finding my own mistakes as I am at finding the mistakes of others. Also, if anyone is interested I have developed excel spreadsheets for most rigging formulas so you can just plug in the weight, sling lengths and other data in to select cells on the colored diagram. I would be happy to share with anyone who wants the file. Just send me an email at michelj48@hotmail.com.

Michael Francis

Posted @ Thursday, March 01, 2012 2:54 PM by Michael Francis

In nearly all ITI programs we round each decimal number to the closest hundredth unless the ten-thousandth number ends in zero.

So the multiplier that you have identified as 1.1166 is rounded to 1.12.

All rounding steps are made in similar manner.

Consider this, that some calculators have 12 positions to the right of the decimal point. Where do we stop?

We opted to use the format as described above.

Thanks for your attention to detail.

We recommend that each person use their corporate guideline for rounding when performing these types of calculations.

Mike
Posted @ Friday, March 02, 2012 12:16 PM by Mike Parnell
señor. michel buenos dias le agradeceria toda clace de informa sobre aparejamiento de cargas y las diferentes tipos de formulas de tension y pesos de los materiaales.. gracias por su colaboracion y cualquier cosa me envia la informacion al correo opcional o al recivido. le agradezco de antemano
Posted @ Friday, May 04, 2012 10:30 AM by german
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