October 24, 2016
Fast Water: What about the substrate?
We chase speed. We seek out marginal gains. For those chosen to represent our nation as Olympic hopefuls, we prioritise athletes with the greatest inherent potential and then carefully monitor what they consume and how they develop themselves through training and ultimately, what power-to-weight ratio they bring into their boat. Their special and, these days, highly technical, scientifically conceived and designed clothing and kit, nutritional supplements for optimal recovery and stamina, plus equipment that includes speed/stroke monitors, cleaver blades and carbon fibre boats, are all conceived and manufactured via the latest technological advances available to yield evermore increments of speed.
But what about the substrate? What about the water? All water is not equal. Hot, cold, salty, acidic, ionised, oxygenated. Does water quality affect boat speed? And, if so, what can we do about that?
Certainly we know that warmer water is faster. Simply put, an increase in water temperature decreases the fluid’s viscosity, where viscosity describes a liquid’s ability to resist flow. Heat makes water less dense, increasing the spacing between its molecules, which leads to less drag force imposed on hulls that move through it.
“If there can be some awareness made then as rowers we can do our bit to preserve water quality.”
Every yachtsperson will know which is faster- saltwater or freshwater. Yet there is good reason for their lack of consensus. Vessels float lower in fresh water so run with a deeper draft. This increase in wetted surface equates to a loss of speed. But the viscosity of fresh water is lower, so there should be less friction produced than in salt water. In fact, the net effect is typically minimal if only the water salinity is taken into account. One common cause for confusion is a conviction that fresh water is noticeably slowing a boat when the hull may be more influenced by the effects of shallow water.
With laments about Rio de Janeiro’s notorious water quality issues regularly making world news as this year’s Olympic Games approach, it’s worth exploring further what amounts to “good” or “bad” water from a rower’s perspective. Water quality is an enduring world concern. In developing countries, around 90 percent of waste water is discharged untreated directly into rivers and streams. 50 percent of rivers flowing through European Union nations do not currently achieve Good Status according to the EU’s Water Framework Directive criteria. Consequently, the World Wildlife Fund (WWF) is spearheading an initiative called WaterLIFE, a campaign funded from 2014-2017 that aims to improve water quality across the EU and also address water quality issues worldwide.
“I want my children to row in clear blue rivers and lakes surrounded by green and filled with life,” says Croatian Olympian Valent Sinkovic.
“You cannot be in our sport, which involves such a close relationship with nature, and not appreciate it and not want to protect it,” agrees Katherine Grainger. “That’s why you will always get rowers who will speak out about it because our sport takes us to some of the most beautiful places and we should never take it for granted. Never assume that those places will always be the same and be idyllic and be looked after. They do need protecting as much as we can”.
Rio is built around an urban delta, where various rivers and canals flow into Guanabara Bay. Venues for Olympic sailing and triathlon events straddle the bay and Atlantic Ocean. Rowing and canoe sprints are to be held on the nearby lagoon Rodrigo de Freitas, which is connected to the Atlantic via a canal. Guanabara Bay not only suffers point pollution from industry on its banks but also receives contamination that feeds into the bay from various rivers.
“The great environmental indicator of the level of pollution in the bay is the Tucuxi freshwater dolphin,” explains Sergio Ricardo, ecologist and director of Bahia Viva. “In 1995 Rio de Janeiro State University identified 800 animals in the bay, ten years later there were 400, and now there are just 35. They’ve been described as the most contaminated mammals in the world.”
Yachtsman Matheus Menezes Gonçalves highlights another problem in the bay. “It gets worse every year. I can see the differences. They’ll improve things for the Olympics, with screens and nets, and we’ll have a “magical week”. But after that it will be back to normal. My grandad swam with the dolphins here in the bay, and now it’s a latrine.”
Water quality is a complex topic with many factors involved but they all relate to water temperature. Parameters include pH, density, conductivity, salinity, dissolved oxygen, CO2, compound toxicity and metabolic rates and photosynthesis production.
Water temperature is much less fickle than air temperature. Water’s low surface albedo enables more energy absorption than reflection and a high specific heat gives water a large heat capacity, meaning that some aquatic organisms may only encounter a 2 or 3 – degree temperature change over their lifetime. Apart from surface water and the littoral zone at water’s edge, which stretches out as far as water clarity enables aquatic vegetation to grow, substantial bodies of water experience only minimal temperature changes due to daily variations in air temperature. Rivers will generally have more temperature fluctuation than lakes and oceans.
From a rower’s perspective, warm water is fast but this does depend on what has caused the heat. Turbidity gives an indication of the amount of suspended solids in water and is an optical measure of water clarity. Particles of less than 2 microns, which is the average filter size, are considered to be dissolved solids. High turbidity brings warmth but also affects photosynthesis by blocking light. And, in upsetting the water ecosystem, turbidity tends to impede rowing speed. Algae blooms are a common example of this. Poor clarity is also visually unsettling as this usually indicates unhealthy water. Pollutants such as dissolved metals and pathogens may be attached to particles that enter the water.
Density is important to rowers, not only because less dense, warm water is faster, but also because anything less dense than water may float near the surface, into a rower’s path.
Due to the bipolar nature of its molecules, water has inherently high surface tension. On a molecular scale, water not only produces friction but also provides some lamination, like lubrication, as boat movement creates a turbulent boundary layer. Water binds to hydrophilic substances with a slight electrical charge but beads up against hydrophobic substances with no charge. Thus oil and water do not mix. Clean water is faster.
Rower Steve McArthur routinely tests the water quality of his local river, the Avon, in Christchurch, New Zealand. As an agricultural consultant, McArthur advises his clients on the impact farming can have and points out problems, such as nutrients like fertilisers that are routinely over-applied to crops “ending up in waterways, which results in unnecessary water contamination”. By advocating better soil management, McArthur has been able to encourage a more cautious use of fertilisers.
“Now we need to stop any more loss of water quality and then improve the water quality. We have to take a long term approach,’ suggests McArthur, “and build up a picture of what is happening with our water quality”. McArthur regularly tests waterways used by rowers and records his findings. “I’m doing it to highlight to the rowing community that we have a problem,” he explains. “If there can be some awareness made then as rowers we can do our bit to preserve water quality. We all want to row on nice water and we want to be able to jump in the water on a hot day and not get sick”.
McArthur is intent on generating more interest among the rowing community. “I figure if I keep highlighting it, then you keep it in people’s minds”.
Water quality testing doesn’t need to be elaborate or expensive as long as the procedure used is careful and consistent and test equipment is in good working order. Always record the water temperature alongside any other measurements.
World Rivers Day will be the last Sunday of September. Why not mark the occasion by launching a commitment to regularly test the local river or lake water used by your rowing club? ROW360
By Donna McLuskie // This article first appeared in Row360 Issue 12.