Sidmouth Folk Week 2009: Measuring the angle of dangle - calculations of gradients at Bulverton campsite, maximum safe angles for caravans and why vehicles get stuck in the mud. Also, some possible solutions!

Folkies have often complained about camping at Sidmouth's Bulverton campsite as being 'like sleeping on a 30 degree slope'. It might feel like an angle of 30 degrees when you try and roll back from where you have ended up in the night, but it isn't.

Here is one observation from a first-time 2009 attendee, posted on the mudcat website 12 August 2009:

My only gripes are personal ones and no reflection on the organisation of the event. Not used to having a campsite so far from the action. The rain on top made getting down for morning workshops etc a grind ... We really could have done with even just straw being put down round by the showers, just to combat the slurry effect. However as the campsite is on about a 30 degree slope (I must admit to getting a tad fed up waking up in a heap at the bottom of the tent each morning....) the water did drain pretty quickly once it stopped raining.... Whoever was cleaning the toilets deserves a medal, as they managed to keep cleaning the floors as well as the toilets themselves!

A 30 degree slope is about 1 in 1.7 - impossible in most motor vehicles. It has been claimed that a Landrover can be driven up a 1 in 1 slope (45 degrees). The most an ordinary car towing a heavy caravan can do reliably is a slope of about 1 in 6 (on a good surface). Hill starts on steeper than 1 in 8 can prove difficult. On very wet grass even 1 in 30 gradient (a mere 1.9 degrees) may prove impossible. Even on a good road, heavily laden goods vehicles can have difficulty on a 1 in 6 slope (or even 1 in 7) because of their low power to weight ratio. A typical car - even when laden - should be able to manage a 1 in 4 hill, but not when towing a caravan. Extreme sports cyclists can manage a 1 in 3 hill (angle 18.4 degrees) but only over very short distances. In a slurry of mud, even a 4x4 fitted with 'motorway' tyres can get stranded on level ground.

There are two important parameters:

the power to weight ratio of the vehicle. This will determine if the vehicle will go up a steep slope at all in a given gear - even if the tyres do not lose grip. Trains can have a very low power to weight ratio and can manage only shallow gradients. They can accelerate only very slowly too.

the available traction at the driven wheels. This can be limited by coefficient of friction and will determine if the vehicle will crawl up a slope even if the power to weight ratio is adequate. It is the critical parameter on folk festival campsites.

This is all explained in the following extract from a faq website: the effort required to move a vehicle has to be delivered via the tyres - if the coefficient of friction is insufficient then no matter how powerful the car, it won't be able to move. 'Grade' is used in the USA instead of 'slope'.

The slope of a road is more useful than its angle because it gives a direct way to assess the effort required to move forward against the grade, whereas the angle in degrees does not readily reveal this information. A 5% grade requires a forward force of approximately 5% of the vehicle weight (above and beyond the force it takes to travel similarly on flat ground). A 15% grade requires a propulsion force of approximately 15% of the vehicle weight. Although the angle may be more easily visualized, it does not convert easily to effort without a calculator. For instance a 20% grade is an 11.3 degree angle and is a steep and difficult gradient. The relationship between angle and slope is non linear becoming 100% (1:1) at a 45 degree angle. In contrast, the SINE of 45 degrees is 70.7% while the SINE of 90 degrees (straight up) is 100% for which the slope (TANGENT) is infinity (or undefined).

Results are presented below of some measurements of gradients on the Bulverton long walk (down from the marquee) and on the Bulverton campsite itself.

All you ever need to know about measuring road gradients is here (and you get background music!). I used the technique they advocate - my piece of wood was 82 inches long, long enough to average out a few local undulations. The angle of the central part of field 2 is only about 7 degrees (Cotan 82"/10"), somewhat less than the subjective impression of 30 degrees! You can calculate angles etc here.

Location Gradient (measured) % slope Angle (o)
Steepest part of the pathway down from the Bulverton marquee 1 in 6.3 15.9 9
Vehicular track up the hill from the road to the Bulverton marquee 1 in 10.9 9.2 5.2
Driving into field 2 - average slopes of the first 30 m into field 2 1 in 10.3 to 1 in 20.5 9.7 to 4.9 5.6 to 2.8
The track down to the showers in field 1 1 in 11.7 to 1 in 13.6 8.6 to 7.4 4.9 to 4.2
The central part of field 2, where caravans used to be parked! 1 in 7.45 to 1 in 9.1 13.4 to 11 7.7 to 6.3

So it is no surprise some people slip up walking down from the Bulverton.

"It wasn't the alcohol my Client had consumed m'lud, it was the gradient and the coefficient of friction. The festival organisers failed to take steps adequately to warn my Client about either of these, and as such they failed in their duty of care. My Client sustained serious facial injuries, to say nothing of breaking one of her fingernails. She has been left irrecoverably traumatised. She may be unable ever to walk again down the slightest grassy incline. Her future quality of life has therefore been seriously impaired. This is reflected, in a modest way, in her claim for 5 million. There is of course also the small matter of loss of future earnings. And of course, there is my fee."

Walking down a 1 in 6.3 slope on grass is more than some infirm people could manage safely in good conditions.

Perhaps the most remarkable result here is that in the days of the old international festival, caravans used to be parked all over the steep central part of field 2 - which in places is steeper than 1 in 8. This is far too steep a slope on which ever to pitch a caravan, especially when there are tents below. Fortunately, only tents are allowed there now and cars have to be parked side-on to the slope. It doesn't look this steep, but I measured it at six or seven different places. These results should serve to confirm the importance of adhering to the rules used in 2009: tents only and cars parked side-on. They also explain the difficulties that were experienced in towing caravans out of this field at the end of a wet week.

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An illustration of why caravans cannot be parked safely on steeply sloping fields - especially if you try and level them.

This 14' model has been raised almost as far as the jockey wheel would allow - were it to have been fully extended and with the wheel on the ground. And don't try this at home! Caravans and trailers can develop a mind of their own when jacked up and disconnected from a towing vehicle.

The principal danger is that they will suddenly slew sideways. This can cause a pillar jack to topple over.

This caravan was raised a little more - until the rear stabilisers were almost on the ground. The slope of the floor was then measured at 1 in 9.4.

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At a slope of 1 in 9.4 the front stabiliser legs are fully extended - and clear of the ground. Were the caravan to be left like this, bricks or blocks would have been necessary beneath the front legs, and if the caravan were then to slew sideways the legs could slide off the blocks. This can happen all too easily on a wet muddy field where tyres can slide on the grass even if the brakes are on!

The danger is increased on a sloping and undulating field where there is little chance of pitching a caravan exactly down the line of greatest slope. There will therefore be a force trying to rotate the caravan, in addition to that trying to make it roll down the hill. Even using the jockey wheel and stabiliser legs as intended - directly onto small pads on the ground - the maximum permitted slope would be around 1 in 10.

Caravans should always if at all possible be pitched on level ground. If this is not possible they should be facing down the line of greatest slope - even if it doesn't give the best scenic view! This will limit any sideslip forces that can cause the unit to slew around. On a steep muddy slope, wheel chocks may just slide, as may braked wheels. It can also be safer to tow a caravan down the line of greatest slope rather than to attempt a shallower descent by going sideways.

The two pictures above illustrate the maximum permitted slope were both jockey wheel and stabiliser legs to be used as intended - and with both at their design limit. Most of the load should always be taken on the jockey wheel with small adjustments being made via the stabilisers. A caravan should NEVER be jacked up on a steep slope (or anywhere else) using just the stabiliser legs. They are not designed for such loads, the bodyshell of the caravan may be distorted and if the caravan slews sideways the legs can buckle and collapse. On a slope steeper than about 1 in 10, none of this is possible in any safety, even if there are no tents further down the hill!

Between (say) 1 in 15 and 1 in 25 a typical caravan could be levelled using the jockey wheel and stabilisers and if properly braked, securely chocked and on firm ground, it should be safe enough. On slopes of less than 1 in 25 there would be less need for 'belt and braces' on firm ground, but still a need for caution on soft ground, especially if tents were pitched on the lower slopes. All of this merely serves to confirm why there were such problems and dangers on the Bulverton campsite in earlier years - see for example this letter from 1998.

Difficulties of getting caravans and motorhomes into field 2, up the slope from field 1 are also easily understood. The measured gradient here is between 1 in 10 and 1 in 20. Even the shallower parts would cause problems on wet grass that had not yet been churned into mud. However, the average gradient would be acceptable were the land to be levelled out a bit and a "cheap and cheerful" rock roadway to be constructed. This is a thought for the future - most the problems of access into field 2 might be solved once and for all. This would give the festival more 'guaranteed' all weather caravan and motorhome pitches. Once the caravans were past the worst of the slope (which they could all manage under their own steam on a good surface) a good 4x4 vehicle with M&S tyres would be adequate to rotate and reverse them into position if the pitch area itself was particularly wet. This would need a few stewards who knew what they were doing!

Once the access from field 1 into field 2 was 'smoothed out' and a rock roadway constructed the gradient might not be much more than down the access track in field 1 - down to the shower block. This has a gradient of about 1 in 12 and lorries managed it most of the time in 2009, despite the rather poor surface. Even ordinary cars towing caravans should easily be able to manage 1 in 12 - or even 1 in 10, provided the surface was sound and they didn't need to do hill starts. One possible danger of a loose rock roadway is that cars attempting hill starts with a caravan in tow could spin their wheels and cause stones to fly out - perhaps injuring nearby pedestrians. In wet conditions, maybe the top part of field 2 could be reserved just for motorhomes - those with good hand brakes and properly chocked when in position. Against that, it might be impossible to move a heavy motorhome if it wouldn't go under its own power, except by using a 4x4 tractor - and you could only pull, not push!

There are options to make life easier on this campsite - but at what cost? One option is to construct a new entrance from the Bulverton road directly into field 2 maybe 250 metres from the existing campsite entrance. This could be quite a costly undertaking as it would need to be splayed for safety reasons (although maybe in one direction only). In fact a gateway exists - it was used in the old days to allow folkies to get back to the camping field from the Bowd marquee. Anyone remember that? Anyone have any photos of the campsite 10 years ago?

But what is the point in attracting more people onto the campsite if dance and concert facilities in town are inadequate at times even for the numbers now attending the festival?


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