Water temperature - effect on boat speed

[Woolygog]

I'm no physicist or fluid dynamics boffin, so...

With ALL other things being equal, what would be the approximate
difference in speed expected over 2k for water temperatures of, say,
20C and 10C?

I assume (see caveat above) that as water is at its densest at 4C,
there should be less resistance to boats at higher water temperatures,
so you'd expect a faster time.

I have not defined any specific boat type (size, scull or sweep). Just
after a general appreciation of the difference...

Cheers!

[Phil]

But.. less dense means that you need to displace more of it in order
to support the same weight. Does this not mean increased wetted area?
A more complex relationship than at first sight...

[Carl]

It is a more complex issue, but this could be a good place to get a
simple rule of thumb:
www.biorow.com/RBN_en_2009_files/2009RowBiomNews12.pdf

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
Email: ca...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)

[AJ]

> Email: c...@carldouglas.co.uk  Tel: +44(0)1932-570946  Fax: -563682
> URLs:  www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)- Hide quoted text -
>
> - Show quoted text -

Is there anything in rowing that is simple ???

When I started as a naive novice in the mid 90's I thought it was all
relatively straightforward - get fit, get strong, (can't say I really
managed either but i got by) drop your blade in the water and 'pull
hard'. Now the more i read in rec sport rowing the more my head spins.
It is all fascinating stuff but sometimes i feel like the schoolboy
character in the Far Side cartoon who puts his hand up in class and
says ' please sir, can i be excused, my brain is full'.

[zeke_hoskin]

On Nov 30, 8:08 am, Carl <s...@sss.jjj> wrote:

I couldn't make Carl's link work, but . . . I did do my undergrad
thesis in fluid dynamics, way back in the Holocene. If you just
consider density, flow resistance is zero. The important quantity is
viscosity, which drops off with rising temperature. Below is a quick
copy of kinematic viscosity vs temperature from 0 to 30 Celsius. Now,
resistance is NOT linear with viscosity, because boundary layer
behaviour changes oddly, but my semi-educated guess is that a given
crew in a given boat will go faster as water temperature rises, up to
the point where body overheating becomes a problem.

Temp Viscosity
0 1.787
5 1.519
10 1.307
20 1.002
30 0.798

[Carl]

The link works OK for me, so I don't know how to help you see it. Sorry

Fluid drag is indeed complex, & both viscosity & density matter.

You'll remember, Zeke, that friction factors are a complex function of
Reynolds number, Re, & that Re = rho*V*L/mu
(rho = fluid density, V = flow velocity, L = a characteristic dimension,
such as distance along the boat from the leading edge/bow or the
diameter of a pipe, & mu = fluid viscosity)

To the non-initiates, Re is the ratio of inertial to viscous forces for
the fluid against the surface, & the higher its value the more turbulent
the flow is likely to be.

Anyway, friction factor at a given velocity falls as Re increases, & Re
increases as water temperature rises, so fluid drag should fall. In the
simple case, however, we know that fluid drag does not fall very rapidly
with increase in Re, so there ain't a big gain for the relatively small
change in Re over a rower's water's likely temperature range.

Complicating things a bit more: the transition point between laminar
(low drag) & turbulent (high drag) flows over a surface moves a little
closer to the bow as Re rises, so more of the surface encounters the
higher-drag turbulent flow regime.

And then there's wave drag......

So I'd accept Kleshnev's 1.3% increase in speed between 5 & 30C as a
good empirical figure. Question is: how are you going to use this info?

[zeke_hoskin]

> Email: c...@carldouglas.co.uk  Tel: +44(0)1932-570946  Fax: -563682
> URLs:  www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)

Thanks, Carl. As to how I'd use this info: well, if I were trying to
set a record, I'd
pick a cold morning on a warm lake at low altitude(more oxygen).

[tetsushi-ozawa]

Effect on Hull, and also on "Blade"

Yes, Water temp - drag hull relation is important.
But, On the other hand,
How about the effect on the "Blade"?
maybe, blade is more effective in lower water temp, higher viscosity.

Tetsushi Ozawa, Hiroshima

[Tinus]

The blade is indeed more effective because the same force is applied at
lower blade velocities meaning less energy loss due to moving the water.
At the end of the equations you'll still get a higher speed because the
energy loss by the blade (which is reduced in colder weather) is smaller
than the energy loss by the hull (which is higher). So when they change
similar (relative) the hull effect overpowers the blade effect.

If the kinematic viscosity drops about 30% (from 5 C to 25 C) it would
result in about 10% increase in speed when only a simple model of hull
drag is taken into account. Like Carl said the speed only increases by
1.3% so there are all kinds of little effects which together decimate
the 10% figure. Another nice and less evident example (like the blade
effect) is an increase of the variations in pitch, yawn and roll which
all reduce speed.

Another complicating effect Water temperatures below 0 C allow much
higher speeds after a small boat adjustment. :)

[Carl]

Aren't you skating on rather thin ice there, Tinus?

I agree with you on the likely effect of viscosity on blade performance
around the mid-stroke, but it adversely affects surface friction along
the blade at both ends of the stroke. So who knows which way the cookie
crumbles there?

As you indicate, if drag was proportional to viscosity (which it is not)
we'd still get a <10% speed improvement for the same power output.

So, who among those of us in northern latitudes is going out to set a
new world speed record for rowing or sculling in February? And have
they properly considered the manifold consequences of aerodynamic drag -
no, not trying to profit from wind-assist, but the effects of higher air
density & reduced air viscosity at lower temperatures?

But were we in time to provide the OP with the winning pub quiz answer?

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf

[Kit]

Try http://www.biorow.com/RBN_en_2009_files/2009RowBiomNews12.pdf

[Chris A]

On Nov 30, 6:05 pm, zeke_hoskin <z...@zekehoskin.com> wrote:

It's Google groups for you. Don't click on the link, paste it into a
browser. Absolutely fascinating.

[Woolygog]

Thanks all - basically my thoughts were confirmed - and backed up by
that rather natty article that Carl kindly posted a link to.
I shall now square as late as possible and only race in the late
summer!
;-D

[William Atkinson]

Woolygog:
There is an answer on my site at:
http://www.atkinsopht.com/row/watrtemp.htm
with some caveats.
Lengths in 2,000m seem to differ on the order of 2.5 for temperature
differences on the order of 20C.
Best regards,
Bill

[fatsculler]

On Dec 16 2011, 11:39 pm, William Atkinson <atkinso...@gmail.com>
wrote:

I thought "Warm Water" was cited for the reason so many Senior World
Best times were beaten at the Junior Worlds in Plovdiv in '99.

[jesus...@gmail.com]

The size of the boat makes a little difference. I found this paper
http://www.rowingsa.asn.au/uploaded_files/document_uploads/Development/CoachEd/Rowing_Science_article.pdf

[Carl]

On 01/02/2012 03:38, jesus...@gmail.com wrote:
> The size of the boat makes a little difference. I found this paper
> http://www.rowingsa.asn.au/uploaded_files/document_uploads/Development/CoachEd/Rowing_Science_article.pdf

Nothing scales perfectly on water :)

An eight, although superficially very similar to a single (& to the
intermediate size classes of rowing shells), runs at a different
Reynolds number (ratio of viscous to inertial forces), Froude number
(ratio of boat velocity to gravitational wave velocity) & Strouhal
number (ratio of stroke frequency to a boat speed defined as number of
boat lengths/unit time), so there must be material, if modest,
differences between their performance responses to temperature-induced
changes in water's physical properties.

Anyone who knows much about this has great respect for the work of Leo
Lazauskas (one of that report's 2 authors), which goes way back and is
signally free from the bullshit which, as we see in another current RSR
thread, pollutes so many pronouncements on rowing equipment design &
performance. (No, I don't get a penny from Leo for saying that).

[Carl]

On 03/02/2012 15:59, Carl wrote:
> On 01/02/2012 03:38, jesus...@gmail.com wrote:
>> The size of the boat makes a little difference. I found this paper
>> http://www.rowingsa.asn.au/uploaded_files/document_uploads/Development/CoachEd/Rowing_Science_article.pdf
>>
>
> Nothing scales perfectly on water :)
>
> An eight, although superficially very similar to a single (& to the
> intermediate size classes of rowing shells), runs at a different
> Reynolds number (ratio of viscous to inertial forces), Froude number
> (ratio of boat velocity to gravitational wave velocity) & Strouhal
> number (ratio of stroke frequency to a boat speed defined as number of
> boat lengths/unit time), so there must be material, if modest,
> differences between their performance responses to temperature-induced
> changes in water's physical properties.
>
> Anyone who knows much about this has great respect for the work of Leo
> Lazauskas (one of that report's 2 authors), which goes way back and is
> signally free from the bullshit which, as we see in another current RSR
> thread, pollutes so many pronouncements on rowing equipment design &
> performance. (No, I don't get a penny from Leo for saying that).
>
> Cheers -
> Carl
>

OOops - Re is ratio of inertial to viscous forces, not t'other way around.