COX"S WEIGHT V.'s SPEED

[Caspar W Bentinck]

There is always a question as to how much overweight coxes slow the
boat. Some high powered sources suggested that you give up a foot for
every pound over each mile rowed. Or more simply a pound/foot/mile.
Does anyone have any other theories or agreements?

[Nick Buffinger]

When I was in college, the story (factoid, rumor, old-wives tale,
whatever) was .2 seconds per pound per 1000 meters. I haven't any idea
if this has any grounding in fact, but I always suspected it was a bit
less than scientifically rigourous. I would love to hear if anyone
knows the basis for this.

Nick
Stanford RC

[S L Ng]

what is the weight of an overweight cox? i am getting worried now. i'm a
cox and i am 58kg! but, i have coxed many crews to victory, including my
own national crew. i guess it doesn't matter if it is a good crew but a
heavy cox would be taxing to an inexperienced crew.

i'm just trying to please myself. any other opinions out there?

LEONG.

[Wldflower3]

I don't know how true this is, but in the erg room at my boat house there
is a poster of what mistakes equal over 2000 meters. According to that,
40 excess pounds will equal a lose by 2 boat lengths (of equal crews)

[Daniel_Eisenberg]

In article <46ftdf$8...@newsbf02.news.aol.com>, wldfl...@aol.com says...

>
>I don't know how true this is, but in the erg room at my boat house there
>is a poster of what mistakes equal over 2000 meters. According to that,
>40 excess pounds will equal a lose by 2 boat lengths (of equal crews)

What other mistakes and what distances do they cause are on this poster?

[David Pratt]

Ken:
As always, your postings are clear, informative and provocative.

If I take the integrated form of your relationship, V2/V1 =
(m2/m1)^-2/9, it is instructive to note that if I were to reduce my own body
weight from 220 to 200 pounds (conceivable if painful!), I could be 35 m
faster over 2000 m in a 50 pound single (boat + sculls).

Is that weight-loss motivating, or what??!!

-- Dave Pratt

(P.S. just for fun: On the other hand, the same formula shows
that my (boat+sculls) would be 780 m faster if I weren't in it at all!)

On Mon, 23 Oct 1995, Ken Young wrote:

> This is asked quite often in this newsgroup. Of course the same question
> is asked regarding the boat weight. The speed loss depends on the total
> weight of the boat and the weight difference with the heavier or lighter
> cox. Of course, heavier crew persons who produce the same power produce
> the same speed loss. Also, you should take into account that the same
> cox will produce a greater percentage loss of speed in a 4 as compared to
> an 8 all else being equal.
>
> For racing shells, it's well founded that the power required to drive it
> depends on v^3 * m^(2/3). The m^(2/3), mass^(2/3) scales the whetted area
> which is the main drag and v is the boat speed. Solving for v and
> expressed as a fractional loss and fractional weight, we have:
>
> dv/v =- 2/9* dm/m
>
> This means that a fractional weight gain of 1% compared to the total
> weight of the boat and crew produces a loss of 2/9% of speed.
>
> For an 8 which may have a total weight of 220 + 8*200 + 120 =1940 lb, an
> extra 1 lb makes a percentage change of .05% in wt and only a .01% in speed.
> For a 2000 m race there is a loss in distance of .23m.
>
> Regards,
>
> Ken Young Tel: 206 543 4186
> Dept of Physics Box 351560 FAX: 206 685 9242
> University of Washington Email: yo...@phys.washington.edu
> Seattle, WA 98195-1560 URL:http://squark.phys.washington.edu/~young/
>
> On 23 Oct 1995, Susan Crabb wrote:
>
> > I have the same question. I am not overweight, but I am very tall for a
> > cox (5'9''). I weigh about 128lbs, and I cox for the novice men at UT
> > Austin. Let me know if my weight is destructive to my crew's abilities!
> > Other than my size, I am a pretty good cox.

[Christie L Pitzner]

Wldflower3 (wldfl...@aol.com) wrote:
: I don't know how true this is, but in the erg room at my boat house there

: is a poster of what mistakes equal over 2000 meters. According to that,
: 40 excess pounds will equal a lose by 2 boat lengths (of equal crews)

I'm curious: what are the other mistakes and equivalents? Please Post!

[johncr...@delphi.com]

Ken Young <yo...@squark.phys.washington.edu> writes:

>For racing shells, it's well founded that the power required to drive it
>depends on v^3 * m^(2/3). The m^(2/3), mass^(2/3) scales the whetted area
>which is the main drag and v is the boat speed. Solving for v and
>expressed as a fractional loss and fractional weight, we have:
>
>dv/v =- 2/9* dm/m
>
>This means that a fractional weight gain of 1% compared to the total
>weight of the boat and crew produces a loss of 2/9% of speed.
>

It is nice to see a little rigor applied to the question.
Weight is a complex issue which will affect the motion of the boat
in different ways critically dependent upon sea conditions and the
rowing style of the crew. I will submit two generalities: 1; weight is
no
[A
not that big a deal. 2; The effect of weight is dependent upon the degree
of acceleration extant in a crew's rowing stroke. -this is obvious
to our quoted physicist, but not always thought about in the motion of the
boat. The more a boat is kept at a constant speed, the less effect a change
in total mass will have in its performance. Note that mass can pull your
boat through the slow spots as well as slow it in the speeding spots.
Crews which tend to a smooth stroke will suffer less detriment from the
heavy coxswain than will those who launch the boat from stroke to stroke.
In terms of the increased wetted surface area and greater cross-sectional
area generated by a coxswain of greater weight, the effects are minimal
[A. There are much more valuable things to worry about when trying
to move a boat.
-JPC, UCBerkeley Lwt
Crew

[grahamca...@gmail.com]

Rowing boat speed pulsates, and this is inefficient.
If the cox sits still, he becomes part of boat weight.Pulsing is reduced.
If he moves back and forth in the stroke he becomes part of crew weight, and pulsing increases.
It would be interesting to see what happens, in a blind test, if boat weight was changed. I would not be surprised if a static 'cox' of even 100kg increased speed.
I saw two calculations showing that the fastest boat weight for a single was 20kg in one case, and 25% of sculler weight in the other.
If you are going to add weights they should be added to the gates of bigger boats, and possibly bow and stern of singles.
Not easy persuading anyone that more weight is faster(if it is part of the boat)!!

[Ali]

> >
> > For an 8 which may have a total weight of 220 + 8*200 + 120 =1940 lb, an
> > extra 1 lb makes a percentage change of .05% in wt and only a .01% in speed.
> > For a 2000 m race there is a loss in distance of .23m.
> >
> > Regards,
> >
> > Ken Young Tel: 206 543 4186
> > Dept of Physics Box 351560 FAX: 206 685 9242
> > University of Washington

So for an 8, if each rower lost just a kilo they would get to the finish nearly a quarter of a length earlier!

[carl]

That's from October 1995! Nothing wrong with that, of course.

But, sadly, Ken passed away some while back.

When we have a crew visit our works (as they are welcome to do), having
discussed boats and bits we get a chance to talk steering. At that
point I ask cox how it feels to be blamed for their weight by rowers who
think that being well-fed makes them stronger & faster. And how it
feels to be blamed for bad steering when all you get to steer with is a
few quids/bucks/euros-worth of flat metal, such as you'd never see as a
control surface on any plane or decent sailboat.

That surprises the rowers, until I gently explain how steering actually
should work (it's to do with fluid dynamics) & therefore how difficult
it is to steer with inadequate kit. And then explain how cox is having
to correct for random soft & hard strokes, & crosswinds, & how steering
with conventional kit incurs parasitic drag, & how much speed you lose
as a result.

Until then, it is grudgingly agreed, if the crew loses it's considered
to be cox's fault & when it wins it's down to the rowers' technique,
weight & power ;-)

But on the all-up weight issue:
There is no requirement for cox to remain static WRT the boat. Indeed,
it's pretty hard to do so since the boat checks & surges so much through
each stroke. Hull drag is increased by these speed variations, so I'm
surprised that no one has experimented with getting cox to move in such
a manner as to reduce their amplitude. A happy cox is a better cox.
The odd kilogram or so really does not matter as it damps the boat's
speed variations while barely altering its displacement, & even less its
wetted surface area & hull drag. But a physically-contributory cox,
working away to counteract the speed oscillations ... that would be
worth exploring - if you really want to win.

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: tinyurl.com/2tqujf
Email: ca...@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells

---
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[magnus....@gmail.com]

My own bit of analysis on this topic is here http://www.slidingseat.net/studies/studies.html#powerofnine

which agrees with the above, i.e. that

dv/v = +1/9 dm/m if the "m" is "power-producing" m (ie extra rower mass)

and

dv/v = -2/9 dm/m if "non-power-producing" m (ie extra deadweight).

Note the change in sign between the two.

Cheers, Magnus

[Chris A]

On Thursday, October 19, 1995 at 8:00:00 AM UTC+1, Caspar W Bentinck wrote:
> There is always a question as to how much overweight coxes slow the
> boat. Some high powered sources suggested that you give up a foot for
> every pound over each mile rowed. Or more simply a pound/foot/mile.
> Does anyone have any other theories or agreements?

Well when they were both Olympic events the WBT for M4+ was about 20s slower than M4- so that's for an extra 56kg.

[Nosmo]

I think your tables are a good rule of thumb, but...

Don't think your assumption that power is proportional to mass/blood volume is accurate. My understanding is that it is close for anaerobic power but for aerobic power the cross sectional area of the blood vessels are a better approximation.

You mention power to weight ratio for cyclists--which is a very good indicator of climbing ability on steep climbs (where the power going into overcoming gravity approaches 100%). If power was proportional to mass, the best climbers would be heavier since the weight of the bicycle would be a smaller proportion of their weight, but lighter cyclists have always been the best climbers.

Also if I recall correctly, one of the BioRow newsletters, came to the conclusion that for a given boat, .16 rather than 2/9 for the exponent for the increase in drag with Mass, was more accurate. Between boat sized 2/9th is theoretically accurate but for a given boat, the change in surface area with mass produced dv/v =.16 dM/M^. In practice there is not too much difference for small changes.

You do mention the coxswain, but I would remind people to not forget about the the weight of the boat when using the tables or formulas.

[carl]

By that 1ft/mile/lb yardstick, it seems the 4+ should be ~47 metres
slower over 2k than the 4-, which looks close to 9 seconds. But there
you have put the heavier ensemble into a longer shell, adding another
variable.

Further, simplistic linear assumptions may have scant validity in the
real situation in which oscillations in boat speed increase, & in so
doing increase a component of hull drag, as boat (+ cox) mass falls.
This means that, for any crew but dependent on their technique, there
will be a finite mass of boat below which total drag is likely to
increase & speed will fall.

I note there have as yet been no takers for my pro-active cox proposal.

[John E]

But a physically-contributory cox, working away to counteract the speed oscillations ... that would be worth exploring - if you really want to win.

I can't find any images, but I remember a US (?) manufactured boat with the Cox on a sliding seat (and it had sideways angled slides for the rowers!). It would interesting to know what it was like to row although the fact that the design never took off presumably means it didn't work too well in practice....

[carl]

On 21/05/2019 13:12, John E wrote:
> But a physically-contributory cox, working away to counteract the speed oscillations ... that would be worth exploring - if you really want to win.
>
> I can't find any images, but I remember a US (?) manufactured boat with the Cox on a sliding seat (and it had sideways angled slides for the rowers!). It would interesting to know what it was like to row although the fact that the design never took off presumably means it didn't work too well in practice....
>

Innate conservatism within the sport might explain that, John. Also, if
the rowers' masses move across the axis of the boat to any degree you
may encounter balance problems. Certainly that was an issue in the days
of yore when racing shells were wider, had shorter riggers & were
side-seated.

None of which need invalidate the idea of putting cox on a sliding seat.

[val...@biorow.com]

On Thursday, 19 October 1995 08:00:00 UTC+1, Caspar W Bentinck wrote:
> There is always a question as to how much overweight coxes slow the
> boat. Some high powered sources suggested that you give up a foot for
> every pound over each mile rowed. Or more simply a pound/foot/mile.
> Does anyone have any other theories or agreements?

"Every 1kg of extra dead weight per rower can decrease the boat speed by 0.19% or about 0.7s slower over a 2k race in 6:00"
see BioRow Newsletter on http://www.biorow.com/RBN_en_2009_files/2009RowBiomNews02.pdf

[Jonny]

I believe it was Pocock who experimented with the angled slide rails. Not sure what they called it... something like bio-rig.