"oarsman" <oarsman101@yahoo.com> wrote in message news:1112322080.836312.228710@f14g2000cwb.googlegroups.com...> As the temperature of water decreases, it's density increases until> the point it freezes, then due to the crystal structure of ice, the> density decreases. So, right at the point that water is about to> freeze, it is at it's most dense. Now, extrapolating this> information, I can only assume that with a given effort a boat is going> to go slower the colder the water. I hope this is true because if it> is not all the erging I did over the winter doesn't really matter.> My question is: "is there a simple formula that I can use to correct> my time for water temperature?" Or, conversely "did I get fat and> lazy over the winter?"
There were suggestions that the unusually fast times at Plovdiv in 1999 might have been at least partly related to the water temperature, but I would expect the effect to be small (remembering that in crude terms if the resistance were proportional to the density, the speed would be inversely proportional to the square root of the density). There will of course be changes in viscosity as well as in density.
Perhaps if it isn't included specifically in http://www.atm.ox.ac.uk/rowing/physics/index.html, Anu might be persuaded to add it? It might, however, be argued that the physiological effects of the temperature change might well be greater than the hydrodynamic effects. -- David Biddulph
David Biddulph wrote:> "oarsman" <oarsman101@yahoo.com> wrote in message > news:1112322080.836312.228710@f14g2000cwb.googlegroups.com...>
As the temperature of water decreases, it's density increases until>>the point it freezes, then due to the crystal structure of ice, the>>density decreases. So, right at the point that water is about to>>freeze, it is at it's most dense. Now, extrapolating this>>information, I can only assume that with a given effort a boat is going>>to go slower the colder the water. I hope this is true because if it>>is not all the erging I did over the winter doesn't really matter.>>My question is: "is there a simple formula that I can use to correct>>my time for water temperature?" Or, conversely "did I get fat and>>lazy over the winter?"d>
There were suggestions that the unusually fast times at Plovdiv in 1999 > might have been at least partly related to the water temperature, but I > would expect the effect to be small (remembering that in crude terms if the > resistance were proportional to the density, the speed would be inversely > proportional to the square root of the density). There will of course be > changes in viscosity as well as in density.>
I've got a graph from a lecture by Klaus Filter from which you can calculate the speed difference rowing in water at 5 degrees C and 15 degrees C as about 1.7%.
On Fri, 1 Apr 2005 07:59:29 +0000 (UTC), David Biddulph wrote:> It might, however, be argued that the physiological effects of the > temperature change might well be greater than the hydrodynamic effects.
Not to mention psychological. Doh! There, I did mention it.
oarsman wrote:> As the temperature of water decreases, it's density increases until> the point it freezes, then due to the crystal structure of ice, the> density decreases. So, right at the point that water is about to> freeze, it is at it's most dense. Now, extrapolating this> information, I can only assume that with a given effort a boat is> going to go slower the colder the water. I hope this is true because> if it is not all the erging I did over the winter doesn't really> matter.> My question is: "is there a simple formula that I can use to correct> my time for water temperature?" Or, conversely "did I get fat and> lazy over the winter?"
Just a few observations:
1. The max density is a few degrees above freezing
2. You seen to be ignoring the fact that the increased density will also mean the shell will displace less water and therefore will have less wet area reducing drag. I have no idea what the net effect will be, but I'll bet it will be very small.
3. Cold muscles are likely to react different.
4. Additional clothing will slow you down. While running I figure 10 or more seconds per mile for sweats vs. shorts.
Bill Atkinson wrote:> The ROWING model <http://www.atkinsopht.com/row/watrtemp.htm> takes> into account the variation of water density with temperature (both for> fresh and sea water); accounts for the change in wetted surface with> density; the resulting variation in Reynolds' number; and the change> in fluid resistance with density.> Need more?> Cheers.> Bill
