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What Size Crane Do I Need?

Introduction

Introduction to Crane Sizes

There are many factors to consider when trying to calculate what size crane you need. In this free guide to crane sizes we focus on covering mobile crane sizes. We have included a simple table that you can use to quickly estimate the crane size you will need based on the weight of your item and the radius (which we will explain further). However, almost no lifting operation is identical and this is the reason that only qualified Appointed Persons should choose a suitable crane size and crane type for your job. This crane size guide acts as a starting point for anyone wanting to approximate the logistical viability of their project and assess the scale of their lifting requirements. If you don’t want to wrap your head around this guide, just get in touch with us via our website live chat, send us and email or pick up the phone and we will offer friendly advice and give you a no obligation crane hire quotation today.

How is this crane size guide broken down?

We first cover the three main factors that influence the crane size you need – weight, radius and height. We then take a look at the numerous other factors that can play a part in determining the crane size you need such as space and crane configuration. Following this, there is a simple crane size calculation chart which helps you to estimate the crane size you need based on the weight and radius of your lift. The following section explains in a bit more detail how to check that a crane is capable of completing your lifting operation by using the crane specification sheet. Finally, this crane size guide summarises the information discussed and explains what you can do to get your definitive crane size and crane hire cost.

Variables

Weight, Radius and Height - 3 Crane Size Influences

When calculating what crane size you need, there are many variables to consider. The three most important are weight, radius and height. A crane size estimate can be based on the weight and radius but the height of the lift is almost equally important when checking a crane size is suitable for a specific lifting operation. If there are no obstructions to the lift, such as buildings, or the item does not need to be lifted high then the height is less important than the weight and radius when determining crane size.

What is the weight, radius and height?

The table gives an explanation of these factors and outlines what affect they can have on the crane size required.

Weight

Quite simply, what is the weight of the item you need lifting? In addition to the item’s weight, there is also the weight of the tackle and crane hook to consider but these can vary depending on the type of crane and the lift.

Radius

How far does the item need lifting? This is the distance from the centre of the crane’s slew ring to the centre of gravity of the load’s furthest position from the crane.

Height

How high does the crane need to lift? If the crane is positioned close to a building, then it will need to telescope out higher to achieve the radius required.

How do I find the weight, radius and height to help determine what size crane I need?

Usually you can find out the weight of an item by looking at its specification sheet – if it does not have one then you will need to contact the manufacturer to confirm the weight. If the weight on the day is different to that used to plan the lift, then you will end up either paying for a crane larger than necessary or the lift will not be possible. The radius is simply measured (in metres) using a tape measure or distance meter – to do this, measure horizontally the distance from the centre of the cranes slew ring in the position it will set up to the centre of gravity of the loads furthest point from this. Finally, the height of the lift can be determined by either the dimensions of the object or obstructions to the lift such as buildings – this should also be measured in metres.

Variables

Other Factors Affecting Crane Size

Weight, radius and height are just three of many factors to consider when determining the final crane size needed. In reality there are many more things to consider when determining what size crane you need and for this reason you should have an Appointed Person properly plan the lift. The table below outlines just a few examples of other factors that can affect the crane size you need.

Tackle / Equipment

The weight of the tackle under the hook can vary depending on the item being lifted and how it needs to be slung – for example, spreader beams may be required and this can significantly increase the weight under the hook and consequently the crane size needed.

Hook Block Configuration

The correct hook block configuration needs to be determined for the lift and this can be affected by a number of factors such as the item being lifted and the weight of the item. Different hook blocks can have different weights and this needs accounting for when considering overall lifting capacity.

Obstructions

Obstructions such as buildings, underground services and overhead cables can all influence where a crane is able to setup. Consequently, this can increase the crane’s radius, main boom and ultimately the crane size.

Railways

When carrying lifting operations over or adjacent to a live railway line, and in all circumstances where a crane and its load can collapse within four metres of a railway asset or property boundary, Network Rail must be consulted at the earliest stage of planning. This can influence where a crane can set up and also the crane size required due to a potentially increased radius.

Confined Spaces

When there is limited space for a mobile crane, it might only be feasible for it to half rig. When half rigged, the lifting capacity decreases and therefore you may need a larger crane size than originally anticipated to be able to complete lifting operations.

Crane Configuration

Sometimes, it may be more economical to have a smaller crane with a fly jib attached to increase the lift radius instead of hiring in a larger crane without a fly jib. Likewise, it is sometimes more economical to hire larger crane with less ballast than a smaller crane with full ballast. Decisions like this are difficult to make unless you are an experienced crane hire professional.

Other Factors

The list really does go on and there are numerous site specific factors that come into consideration when determining what size crane and what type of crane are suitable for your job. Synergy Lifting provide a full contract lift service – get in touch for your free advice today and to get your tailored quotation.

Specificaiton

Checking Crane Size With a Crane Specification

Before you try to wrap your head around this information, you should understand that we can work out the suitable crane size for you – this information is for anyone who wants to learn more about the process and to give a brief insight into the methods involved. When you have used the crane size estimator in the section above, find the technical specification sheet for a crane of that size and you will be able to see if it is capable of doing the lift. As an example, we have illustrated this for you to show you how you can check that a crane size is suitable by drawing a few lines on a crane specification sheet.

Step 1 - check the crane dimensions and outrigger base

You must first locate the page illustrating the cranes dimensions. This will allow you to see if the crane will fit in the desired position on site based on the crane size dimensions. Note that the crane will need to drive into position and then extend its outriggers. Click the image and you can see that the outrigger base for a Demag AC 50-1 mobile crane is 6.85m by 6.4m and the overall length of the crane is 11.2m.

Step 2 - position the crane

If the crane fits in the desired location on site, you must then make sure that you plot any potential obstructions to the lifting operations on the graph. In our example, let us assume that the crane is set up 8m from the edge of a tall building. We begin by measuring and plotting 8m along the horizontal axis – this is equal to distance from the centre of the slew ring to the edge of the building that is a potential obstruction to the lift. In the image, this is illustrated by a red line.

Step 3 - height of obstructions

Now that we have plotted the distance from the crane to the building, we need to plot the total height of the building. We need to do this to ensure that the crane’s main boom will be able to reach over the building to achieve the desired radius. Make sure you have an accurate height for the building because this can affect the crane size and ultimately the cost for your crane hire. In our example, the building is 12m high and this is illustrated by the pink line in the image which has been plotted on the graph.

Step 4 - plot the radius

Now that you have the crane set up in the correct location relative to any obstructions, you need to plot the radius that you need the crane to reach for your lift. This is measured in metres from the centre of the crane’s slew ring to the furthest location of the load being lifted. In our example, the desired radius is 16m and this is illustrated by the green line drawn vertically from the 16m mark on the horizontal axis.

Step 5 - plot the main boom

Now that we have the desired radius plotted, we need to make sure the crane can achieve this whilst avoiding any obstructions we have plotted. To do this, you must draw a straight line that from the centre of the crane’s slew ring until it intersects with the line drawn for the radius measurement (i.e. the green line) whilst avoiding any obstructions (i.e. the pink line). Also bear in mind that there should be a comfortable amount of room for any margin for error in the measurements taken for the obstructions height. In our example, this step is illustrated by the blue line.

Step 6 - check the main boom length

The final step to complete using the graph plot is to determine the minimum main boom length required for this lifting operation. In our example, this is illustrated by the orange line drawn on the image – following this back we can see that the required minimum main boom length in our example is 37m.

Step 7 - check the lifting capacity

Now you have the checked that the radius can be achieved and you know the required boom length, you must turn to the corresponding lifting capacities data table – usually the previous or the following page in the crane specification. There are often numerous lifting capacity data tables based on the cranes setup – e.g. the total counterweight / ballast and whether it is fully rigged or half rigged. Start with the first lifting capacity data table and identify the radius and main boom length – in our example this is a 16m radius and a 37m main boom length. Find where these intersect and that is the maximum lifting capacity – in our example the crane can lift 5.6te based on our working ranges (sometimes it can be beneficial to increase the main boom length because it can increase the lifting capacity in some cases). Note that this lifting capacity data table is for the crane setup with 9.5te of ballast and fully rigged. It is worthwhile checking the other lifting capacity data tables to see if the lift can be completed with less ballast because this can often mean you can either use a smaller crane size or the crane can travel with less ballast which can be cheaper.

Summary

What Size Crane Do I Need?

To summarise, calculating the crane size you need can be a bigger task than first expected. There are many factors that need to be accounted for. The main factors are weight, radius and height but it is also important to go beyond this and consider other factors such as obstructions, space and the crane’s configuration. Using our crane size chart above is a good starting point if you are trying to get a rough idea of the approximate scale of your lifting operation but it is important to have an Appointed Person determine the actual crane size and crane type that is required for your project.

How do I know for certain what size crane I need?

Finding out that there is no easy way to work out the crane size you need might seem frustrating at first but luckily for you this need not be a problem for you to solve. At Synergy Lifting, we offer free advice and supply crane hire and contract lift services across the UK. Use the live chat on our website and we will help to calculate the size crane you need and give you an indication of pricing. If suitable, we can conduct a free site visit to discuss your crane requirements with you and come to a firm crane hire cost – feel free to get in touch today.