This lesson will discuss how to use the Tie Down Lashings. Refer to tables in pages 267-280 of the LRG.
Choosing the right table
Once you have the mass of the load, whether the load is blocked or unblocked, the headboard rating, the lashing type, the friction surface category and the angle of the lashing you need to choose the right table.
The first thing you need to determine is whether you should be using a blocked or unblocked table.
If the load is not blocked by a headboard or if the rating for the headboard is less than 0.3 of the mass of the load you should use an UNBLOCKED table.
If the load is blocked by a headboard with a rating greater that 0.3 of the load you can use a BLOCKED table.
The next thing you need to determine is what type of lashing you are using.
The tables in the load restraint guide provide guidance on 7 combinations of Lashing/ Tensioner/Pre-tension.
|Lashing/ Tensioner/ Pre Tension Combination
|Page No for Blocked
|Page no for unblocked
|8mm Transport Chain/Turnbuckles/1000kgf
|8mm Transport Chain/Over-centre Tensioner/750kgf
|50 mm Webbing straps/ Pull-down hand rachet/600kgf
|50 mm Webbing straps/ Push up hand rachet or truck winch/300kgf
|35 mm Webbing straps/ hand rachet/250kgf
|25 mm Webbing straps or 12mm rope/ hand rachet or double Hitch/100kgf
|12mm rope/ Single Hitch/50kgf
The details of the lashings/tensioner/Pre-Tension information are show just above the blocked/ unblocked sign.
Once you have found the right table the next step is to determine which bit of the table you should use.
To do this you need to know the friction coefficient and the angle of the lashings.
Page 243 of the LRG provides the following table which provides you information on typical friction coefficients.
Page 243 of the load restraint guide cautions that these figures are only a guide and recommends you should test to find out the actual coefficient for your specific load and vehicle. Page 243 provides some additional discussion of potential issues.
Once you have determined the friction coefficient you need to work out the lashing angle.
The angle of the lashings is very important. As was discussed in lesson 1.2.2 the frictional force provided is proportional to the force applied to the load at right angles to the load surface. However, where lashings are angled not all of the force will be at right angles (normal) to the load surface. The following table from the load restraint guide.
Luckily you do not need to remember your high school trigonometry to work out the normal force because the tables in the load restraint guide take this into account. If you are interested in how this works there is an explanation on page 244 of the load restraint guide.
Armed with the mass of the load, the friction coefficient, and the lashings angle you are ready to work out which section of the table is relevant to your load and vehicle. Add in animation which shows the friction coefficient and lashing angle and then identifies the number of lashings for the load.