When B&A Engineering (later known as Wylie Systems) produced the first ASLI (automatic safe load indicator) in the 1930’s it was not legislation that drove its development, but good common sense, and the dedication of those crane engineers from a different era, who recognised that a crane was a dangerous animal, and that the crane driver needed all the help he could get.

This sound engineering thinking is more important than ever with today’s designs where materials and methods of construction have made the crane a highly efficient machine. Long gone are the days when a crane operator could claim to be able to drive “by the seat of his pants”.

The authors of this article are (unfortunately!) old enough to remember the SLIs fitted in the 60’s and 70’s and 80’s and we must admit that we were out in the field cutting Wylie DLT cams and installing Weighload indicators at the time when they were current products. Although these mechanical and hydrostatic systems were laborious to install and calibrate, they did provide real assistance to the crane operator. Over the years, we are convinced that they have saved many lives. They were robust devices with long term working capability (given good maintenance) and are still in service on many cranes today, accounting for a certain percentage of the ‘missing’ SLI’s.

The last thirty years have seen huge advances in crane design, increased lifting capacities to weight ratios, increased safety in control, and many more ergonomic improvements in driver comforts and instrumentation. The cranes of today cannot be compared to those of thirty years ago.

The single most important aid to safe crane use, be it a humble 10t yard crane or a 1000t floating crane, is the SLI (safe load indicator) now known as the rated capacity indicator/limiter. Its virtues and failings always spark debate from crane engineers, but it has been at the centre of making cranes safer for much longer than thirty years. The problem from a safety point of view is that the inherent advantages of an indicator system do not necessarily imply that one will be employed in a real world scenario.

Regrettably, it is usually only after a disaster or a significant accident, often with tragic loss of life, that societies react to events by introducing legislation, and this was certainly true in the UK where loss of life in the construction industry resulted in the introduction of “The Construction (Lifting Operations) Regulations 1961”, which required all cranes in the UK with a lifting capacity of over one tonne to be fitted with an “Approved” SLI and a radius indicator.

Many of the cranes produced in the UK at the time were already being fitted with some form of safe load indicator, but the accuracy of the device had to be approved by the then Factory Inspectorate, now replaced by the Health and Safety Executive.

This approval test was thorough and far reaching, and in itself did much to improve the performance and development of SLIs not only manufactured in the UK but also, over time, those from other manufacturers from Europe and Japan.

Bob has personal knowledge of this procedure, as he was present and worked with the Factory Inspectorate on Kruger and PAT UK approval tests. Eventually these approvals led to the issuing of a “Specification for Automatic Safe Load Indicators” by the HSE which would become the basis of British Standard BS7262 in 1990.

The next development was triggered by the growth in popularity of the telescopic crane in the 60s and 70s, this proved to be technically challenging for the SLI industry. Multiple duty charts, longer booms (that deflected under load) and the introduction of fly jibs on telescopic booms, all pushed the old mechanical and hydrostatic systems to their limit, so that when a company called Ekco came onto the scene with an electronic SLI many manufacturers were quick to adopt the new technology.

Stuart Anderson may be correct in the fact that these systems were unreliable and needed high maintenance but in many ways these designs led the industry into new technologies that were the forerunner of the micro-processor systems of today. Many of the early electronic systems produced by Wylie (X3 Loadwatcher, WW225 etc.), although nowhere near as reliable as current production systems are nevertheless still in use.

Did Ekco do as much harm to the crane industry as Anderson said in his presentation? As the saying goes “there’s no gain without pain”. Anderson relates the problems Coles cranes had at the time with Ekco systems, but in truth it was not only Coles that used Ekco. PPM did in France, and there the Ekco dealer (Ascorel) was very good at keeping the electronic systems working, and subsequently used the technology to develop its own systems.

It is very easy to knock products in hindsight, but good new ideas should never be stifled – this is called product development. The marketplace is very good at determining the good and the bad, with poor products being quickly dropped. Here we are at B&A Engineering some seventy years on, still producing state of the art systems and with more knowledge and experience than most in the industry today.

Stuart Anderson argues that the PAT Maestro system allows low-cost upgrading of SLIs in the field. The Maestro allows a user to replace the computer component of an ageing and defective PAT SLI unit while retaining the rest of the original system.

Anderson’s enthusiasm may be misplaced. No matter how laudable it may be in principle to provide the industry with low cost upgrades, the Maestro is designed to replace only the DS50, DS100, DS150, and the basic unit of the DS350.

In a crane over ten years old, the various sensors, the cabling and the connectors are the most likely cause of faults and reliability problems.

The Maestro may be able to transfer over the original calibration data, but in the real world, after ten or twenty years of work and subsequent wear, a telescopic crane will have different boom deflections, and the ram friction forces are very likely to have changed appreciably from the initial calibration data.

The suggestion was made that this swap out of components could be done in an hour or so following a working day, with no load testing being required. We strongly disagree with this idea.

Our view is that load checks are the only way to be sure that an SLI is working correctly, and this should not only be in countries like the UK where legislation requires it, but should be applied as good practise wherever cranes are working in the world:

BS 7121-2:2003, 9.8.1 , General

At least every 12 months the calibration of any RCI/L [rated capacity indicator/limiter] device should be verified by the suspension of calibrated weights.

Thorough examination should include confirmation that the calibration of the RCI/L has been checked by the suspension of weights on the crane. A calibration check should also be carried out when any major repair or modification has been carried out on the RCI/L …”

Wylie Systems has always engineered their products with the retrofit market in mind, with calibration carried out directly from the display obviating the need for specialist calibration equipment. We are also more than willing to provide training for the installation and calibration of our equipment either on-site or at our offices.

Our company, and other SLI manufacturers also present in the room were strongly criticised by Anderson for not doing enough to promote the use of SLIs in less developed countries.

We believe that this criticism is inaccurate, poorly researched and offensive. Wylie Systems maintains a worldwide agency network and promotes our safety systems vigorously and with excellent pricing. Our systems are in use all over the world and we back our products with telephone support and spare parts in many instances for products that we supplied twenty or more years ago.

If we consider that the system in the field would be better upgraded to a new system either on technical or commercial grounds, we will supply the correct and best value engineering solution on a case-for-case basis. If the existing sensors are in good working order, we are happy to incorporate them into the proposal and pass on the cost savings to our client.

Within reasonable commercial limitations, we promote an understanding of the increased safety provided by the use of an SLI, and are active in exhibitions and seminars around the world. We are always willing to provide training to engineers to allow independent support of our systems locally; also all our systems can be calibrated and maintained without recourse to specialist equipment.

Another factor is the availability of local ‘low tech’ indicator systems, supposedly, but not actually built to approved standards. A situation in Hong Kong could be cited as an example. This was the only occasion we know of where, following an accident some years ago, legislation was put into place to install SLI systems to all cranes already in use. Gary has personal knowledge of this as he was working in Hong Kong for some months to assist in the extraordinary task of installing and calibrating a large number of indicator systems in a very short period.

Following the initial surge of installations, local companies began producing ‘indicator systems’ which fell far short of European standards, but in the Hong Kong environment at that time any indicator was regarded as an acceptable alternative to none. This damaged the market for full specification indicator systems, and thus compromised safety. It is not acceptable to have standards in place if the people supposedly enforcing these standards have no understanding of how they should be applied.

The reality is that many indicator systems that have been sold over the years are being maintained by their owners in good working order, as our healthy spares sales will testify, some of these being in the order of twenty to thirty years old. We also maintain many of the older systems directly, with our own field service engineers and agents, both in the UK and abroad. I am sure that other SLI manufacturers would report the same.

The countries where we do little service work are the same areas that have no legal obligation to have a functional indicator in place. These tend to be the same countries where, for economic reasons, the older and therefore cheaper cranes tend to be imported.

So, our belief is that the answer to the question raised in the article ‘The missing SLIs mystery’ is that the vast majority of the indicator systems which have ‘vanished’ are simply fitted to old cranes which tend to gravitate to those countries where an SLI is neither required by legislation nor required by the crane owner, where they are either scrapped or left in a non-functional state, even though this puts the crane and personnel at risk. No great mystery here, just market forces at work.

Gary Kennedy and Bob Crompton,

Rayco-Wylie Systems UK