Channel 4 – Scrapheap Challenge 2004

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Scrapheap Challenge 2004

Quarter final C – Power Rowers

Science

General science
The designs

General science

A bow to the past

The Ancient Greeks and Vikings are probably history's best-known rowers, using it as a means of propulsion for hunting, trade and war long before it became a sport.

Greek triremes used multiple banks of oars – sometimes in as many as four tiers. They were very quick boats and were manoeuvrable with a massive spike on the front for ramming enemy boats.

Rowing as a sport started on the Thames, which continues to be a famous venue for rowing with the Henley Royal Regatta, started in 1839, and the Boat Race between Oxford and Cambridge Universities, which has been held on its waters since 1829.

Rowing sports like Dragon-boat racing (more of a paddling motion) and Cornish gig racing are becoming more and more popular.

Putting your oar in

If they were going to achieve anything like a Pinsentian turn of speed, our teams were going to have to learn to mimic the rower's action:

Catch – As the rower starts, he is bunched forward on the seat – he lifts his arms and the oar is placed into the water vertically (squaring).
Drive – The rower's legs push back and the arms pull back dragging the oar through the water.
Finish – As the rower finishes the stroke, he pushes down, raising the blade while simultaneously tilting the oar (feathering) so it turns horizontally and comes cleanly out of the water.
Recovery – The oar is out of the water as the rower assumes a knees-bent position, the rower begins to raise his hands ready for the next stroke. For the maximum efficiency, this has to be done in a single, smooth action on a stable boat and in synchrony with the oars on the other side of the vessel.

In short, the machine that could get the most power out of the most strokes per minute would win the day.

Overcoming this challenge would involve each team building a machine capable of carrying out a complex series of actions relying on bodged-together parts and the flexibility of a number of Newtonian laws.

The designs

The Anoraks' Morris Minor Rower

Things didn't start well for The Anoraks as they couldn't find anything resembling a hull. Instead, they planned to make do and mend by combining the engine from a Morris Minor with the hulking yellow remains of a 1.5-tonne conveyor-belt surround.

The U-shaped conveyor surround was heavy, full of holes and ungainly but, with the addition of some rowlocks mounted on an outrigger, its elliptical UJ drive could be adapted to turn the oars.

The Anoraks did get lucky when they found the Morris Minor's axle brackets precisely matched the width of the conveyor hull – the wheels hung down neatly on either side as if by design.

The oars were attached and as the wheels turned, the oars flicked up and over, roughly creating a rowing mechanism. It was not pretty, it made a lot of splashes – signifying wasted energy – but it worked.

Making the whole thing ship-shape, though, took a lot of effort. The hull needed plates welded onto it at the seams and these needed waterproofing with a lot of expanding silicone foam and yet more welding.

The Anoraks also sacrificed valuable buoyancy by cutting down the size of the hull and over-complicated matters by building an angled bow which they eventually ditched in favour of a ramp-style front at the close of play.

The steering mechanism used the Morris Minor's differential as a brake as well as a massive rudder.

This boat relied on a wonky chain drive from the prop shaft to power the axles at the top of the boat, which drove the oars, which were in turn, held on with a wing and a prayer.

Chain drives have a history of causing trouble on Scrapheap Challenge and given how Lyndon, the helmsman, handled the heap quad bike, restraint was going to be in short measure.

The Maximus Automata Purist Power Rower

The Bath boys made life easier for themselves by finding a large old boat to use as the basis of their design. By adapting the engine from an old cement mixer, they planned to power a single camshaft with a reciprocating rod – rather like a steam train.

The idea was to couple a camshaft to the wheel of the mixer which would rotate the oars, which were attached to dogleg cams coming off a framework running down the centre of the boat. By mounting the rods through a pivot point, they hoped to create a teardrop shape and produce a realistic rowing stroke.

The advantage of the cement-mixer engine was its low rev rate, which meant it would be comfortable operating at low speeds, which would reduce the stress on the bodged-together oars.

Their calculations needed to be spot-on otherwise they were going to end up pulling and pushing with their stroke and going nowhere. They got around this rather neatly by building the two dogleg cams. Each of these was linked to rods that were linked to the individual oars.

The low revs of the cement mixer meant the Maximus' boat was not exactly fast but the ergonomic hull would glide through the water quite happily.

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