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Brogborough Whirl
by Geoff Wheeler
- December 2003
A proposal for a boat lift known as the Brogborough Whirl for the Bedford
and Milton Keynes Waterway
Introduction to the Brogborough Whirl
One of the challenges to building the new Bedford to Milton Keynes canal is
to devise an innovative way to transport boats up and down the Eastern side of
Brogborough Hill – a climb of 30 metres. This proposal sets out a possible
solution which is relatively straightforward to construct and uses simple technology
yet is unique in the British canal system.
Construction of the Brogborough Whirl
The plan is to build a concrete spiral which encloses a marina, visitor centre
and car park. The structure is landscaped to blend in with the surrounding countryside
using spoil from the marina excavation and from other areas of the canal – thus
making a considerable saving on the cost of disposal. The upper end of the spiral
is accessed by a gently sloping straight section on an embankment leading from
the hillside. Similarly at the lower end a straight section slopes to the lower
ground level. At each end of the spiral, boats are floated into watertight steel
caissons which run on rails. This loading/unloading operation uses both technology
and methods already developed, tried and tested on the Falkirk Wheel.
An important feature of the scheme is that the caissons run in dry concrete
channels such that they are largely hidden from view. From a distance, visitors
will observe just the boats apparently floating up and down a grass embankment.
As well as the aesthetic considerations this arrangement provides an added safety
feature. If a caisson became derailed there would be no possibility of it falling
down the hillside.
Scale
The spiral is on average 200 metres in diameter. With a lead in and out of
50 metres each, the track length is approximately 728 metres or just under half
a mile. At a speed of 3 mph, journey time is 10 minutes – about the same
time as going through a single lock. For a fall of 30 metres this gives a gradient
of just 1: 24 or less than 2.5 degrees. Caissons are 22metres long, 5 metres
wide and 1 metre deep.
The model pictured is made to a 1: 400 scale
Methods of propulsion
Although the Brogborough Whirl caissons are heavy, (estimated at 140 – 180
tonnes), with such a slight incline the force required to raise each caisson
is much reduced, being some 5% of the weight. The weight would be distributed
across perhaps 20 axles.
There are a number of possible methods of propulsion.
The most energy efficient is a cable system where the downward caisson pulls
the upward caisson via a rotating drum at the top end. A greater downward weight
is required and this could be achieved by flooding a supplementary tank in the
downward caisson or more simply by just filling the caisson to a greater depth.
An extra depth of say 10 cm would increase the weight by 11 tonnes.
(Note that since a boat displaces its own weight of water, a caisson with
two boats in it would weigh the same as one containing just water.)
The cable runs in a slotted tube beneath the floor of the channel guided by vertical
and horizontal rollers. Removable or hinged steel plates allow access for maintenance.
If a cable system is used it will be necessary to stagger the loading / unloading
points at each end to compensate for the differing lengths of the inner and outer
tracks.
Alternative methods of propulsion include using a diesel or electric motor
on each caisson – possibly with a rack and pinion system, or even a linear
induction motor.
It may be advantageous to use solid tyred wheels running on the flat concrete
bed of the channel rather than rails, at least in the centre section of the caisson
where the curve of the track may require some lateral movement of the wheels.
Brogborough Whirl Visitors
Centre
The Brogborough Whirl's visitor centre is circular with a central
passenger lift. Its roof forms a viewing terrace and seating area for a cafeteria
/ restaurant (which could revolve if funds permitted). Above the terrace is a
control tower which houses the control mechanisms.
In addition to the restaurant, the visitor centre houses an exhibition showing
the history and construction of the canal, an audio/visual theatre, a souvenir
shop and a chandlery supplier.
Visitors can also explore a Brogborough Whirl visitor trail which follows
the tracks to the top of the hill. The gradient is such that most wheelchair
users and parents with prams should have little difficulty in climbing the hill.
It will be necessary to provide some kind of low-level barrier to prevent pedestrians
and dogs from straying onto the tracks.
For less able people it would be beneficial to have some other means to get
to the top such as a ‘cliff lift’ or even a cable car from the top
of the visitor centre if funds permit. A small viewing area is also provided
on Brogborough hill.
Car Parking
A small car park is provided for disabled users within the Brogborough Whirl
arena whilst the main car park is underground and is accessed from outside.
Accommodation Units
There is provision for a number of energy efficient underground ‘eco-homes’ set
in the grass embankment. The model shows 2 such homes with balconies providing
spectacular views across the surrounding countryside
Retail Outlets
Craft workshops are provided near the Brogborough Whirl Marina.
Water Transfer
There will be times when it is necessary to transfer water from the top to
the bottom level. This could be achieved with a pipe sunk into the hillside;
however, the water could be put to a number of good uses.
1. It may be possible to drive a small turbine which would generate electricity
to power the visitor’s centre.
2. A channel could be constructed on the inner rim of the embankment to provide
a ‘White Water Raft’ or ‘Log Flume’ ride as part of the
activity area. This would terminate in a pool which would be an offshoot of the
marina.
3. The same channel could also be used for canoeists.
Activity Area
The embankment within the spiral provides an ideal site for a variety of activities
for all ages. As well as the ‘White Water Run’ mentioned above there
are opportunities for abseiling and rock climbing areas. Rope slides and skiing
either on grass or plastic are other possibilities. The arena is an ideal venue
for small scale concerts, firework displays etc. A riding school could also be
incorporated within the complex.
Sustrans
The site runs within a few miles of the national Sustrans long distance cycle
network and it would be possible to link into this system.
Conclusion
The Brogborough Whirl provides a unique and spectacular dimension to the new
canal which will provide a much needed boost to the tourist industry in this
region. The scheme incorporates a whole range of activities to suit many interest
groups helping to make this truly a ‘Waterway for all’.
Calculations
Track length -
Diameter of ‘circle’ (approximation as this is a spiral) = 200metres -
Circumference is 2?r = 200 x 3.14 = 628m
Track length = 628 + 50m straight sections at each end = 728m (796yds)
Gradient -
Height of hill = 30m -
gradient = 728 ? 30 = 24.26 gradient is 1: 24 approx - Angle of incline = cotan
(30 ? 728) = 2.36?
Weight of caisson
Volume = 5m x 22m x 1m = 110 cu. m.
Weight of water = 110 tonnes
Estimate weight of steel 30 tonnes
Total estimate = 140 tonnes
(nb if caissons are required to have a greater depth then for each additional
10cm add 11 tonnes )
Force needed to raise weight on an inclined plane
Force acting along plane = weight x sin angle of incline
Angle of incline = 2.36? Force = weight x 0.04 or approx 4% of weight.
Volume
Assuming:
• Height of hill is 30m
• Diameter of spiral is 200m.
• Inside slope = 60 degrees
• Centre flat top section is 18m wide
• Outside slope = 30 degrees
• Track length is 728m
Volume is 441,500 cu. m
