Row360 - Issue 2 - Carl Douglas article

[thomas....@googlemail.com]

I was given a copy of the new Row360 magazine along with a new set of Crokers M39's that I bought this week and thought i would just post here to thank Carl for his article on the science behind boats and the fluid dynamics of rowing. This edition was talking about several points including how wind drag can affect the boat speed (and how you can reduce it) and I am very impressed with how well the information is clearly presented and explained to a layman like myself. I definalty would recommend supporting the magazine if you're interested in some very high quality articles about all aspects of rowing and checking out the articles (also some good interviews with Dan Tapolski, Kim Crow, articles on HOCR and the world cups summaries, theres a lot of content!)

You can pick up a copy here and/or take out a subscription

http://www.row-360.com/subscriptions.php

Personally I think ill go for the digital only subscription option with the saving that adds

Now Carl, i just need to work out how to implement the modification to my new blades that you outlined in the article...... :)

[Kit Davies]

So, anyone know how to set up a subscription? Going to the subs page
allows you to pay for one, but not create the username/password needed
to read the magazine online.

Kit

[Kit Davies]

Ok, question answered. My welcome email took a while to come through.

Kit

[Carl]

On 24/09/2014 11:41, thomas....@googlemail.com wrote:

Happy to discuss :)

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

[usbrit]

I subscribed, took a quick look on my computer at work then looked forward to some time at home last night to read it properly

Disappointed the on line version is not iPad friendly

Looks like I'll have to wait for the paper copy

[thomas....@googlemail.com]

Curious to read it is not iPad friendly, how do you mean?

[usbrit]

you need Adobe Flash Player

[Kit Davies]

Also note the following from the ReadMe.txt file:

�Offline Version� is a term used to describe the edition viewable
outside of a web browser, and not independent of an internet connection.

So you still need to be online to read the offline version.

Minor gripes though IMHO. The content is excellent.

Kit

[s...@ku.edu]

Carl, What are your thoughts/observations about the aerodynamics of the now ubiquitous bow-wing rigger? Steven M-M

[John Greenly]

On Wednesday, September 24, 2014 1:37:10 PM UTC-4, Carl wrote:

> On 24/09/2014 11:41, thomas.k.carter wrote:
>
> > I was given a copy of the new Row360 magazine along with a new set of Crokers M39's that I bought this week and thought i would just post here to thank Carl for his article on the science behind boats and the fluid dynamics of rowing. This edition was talking about several points including how wind drag can affect the boat speed (and how you can reduce it) and I am very impressed with how well the information is clearly presented and explained to a layman like myself.

> Happy to discuss :)

> Carl

I just read the article and I think it's excellent! Very good to see the numbers showing the importance of wind drag. I also think Carl did a really nice job of explaining briefly and simply the basic character of the flow and wave generation around a hull, a subject that is really quite complicated and full of pitfalls for the explicator. When I try this, I usually start by saying that the boat is basically a hull-shaped hole in the water, and when you move the hole (hull) forward, the water has to flow backward to get out of the new location of the hole and to fill in behind, where the hole was. The basic point about the pressure field around the hull, namely that there is higher pressure at the bow and lower pressure further aft, then becomes clear: the pressure drop aft from the bow accelerates the water to make it flow astern. Somewhere near or behind the stern the pressure has to increase again to bring the water to a stop as it fills up the hole. But that never entirely happens, for several reasons, and therein lies wasted energy and drag.

This reminds me: for those interested in the full, complicated story, I discovered recently that the Wikipedia article on lift (search "lift force") is quite excellent, perhaps the best I have seen, and it discusses many of the pitfalls in the way of correct understanding. Gives a very clear explanation of the incompleteness of both the simple Newton and Bernoulli explanations typically given. The most fundamental point is that for the flow to follow the curve of the upper surface of a wing it must be deflected downward, and in a fluid that can only happen because the pressure is lower at the inside of the curve- the wing surface- than it is far away, so that the pressure gradient pushes on the fluid perpendicular to the streamlines (flow direction), deflecting the flow into a curve. But by the same token, this says that the fluid must also be accelerated along the streamlines as it flows into that low pressure region, so it flows faster near the surface than far away. That is Newton's laws at work, and you can see that the accelerations along and perpendicular to the streamlines are inseparable- a wonderful consequence of the definitive characteristic of a fluid: it can't sustain sheer stress. That's really the heart of the lift phenomenon. Bernoulli adds to the picture by telling us exactly how the velocity and the pressure are related along a streamline. All of this is the same thing that happens as the flow is deflected and accelerated around the curved surface of a boat hull; in fact flow fields around the boat hull are rather similar to the fields around the top surface of a lifting wing, and you will see that nicely in an animated simulation if you look at that article.

Anyway, kudos to Carl!!

cheers,
John G

[Carl]

On 27/09/2014 14:21, s...@ku.edu wrote:
> Carl, What are your thoughts/observations about the aerodynamics of the now ubiquitous bow-wing rigger? Steven M-M

I might get to discuss this topic in a later Row360 article, so I'll
keep this brief now.

If comparing the bow-mounted with the aft-mounted wing, in awerodynamic
terms there's no advantage for the bow-mounting. The alignment of the
stays is irrelevant (raked astern or raked forward) - successful
aircraft have been made with wings swept in both directions. Swept
wings are needed only when operating at Mach numbers >0.5, at which
speeds you'll get local regions with wind speeds much closer to Mach 0.8
(80% of speed of sound) where sonic effects start to create a bundle of
additional drag. By contrast, a racing shell typically experiences
winds of around M 0.025.

Because bow wing stays must be longer than aft wing stays, for equal
design specifications the bow wing must offer more surface area to the
flow & thus have somewhat greater wind drag.

FWIW - the stiffness demands imposed by the longer bow-wing stay
(stiffness is inversely proportional the the cube of stay length at the
same cross-sectional shape) have been seen in the large diameter of
plain tubular bow wings.

Cheers -

[robin_d...@hotmail.com]

On Sunday, September 28, 2014 4:00:32 PM UTC+1, Carl wrote:
> On 27/09/2014 14:21,

>
> > Carl, What are your thoughts/observations about the aerodynamics of the now ubiquitous bow-wing rigger? Steven M-M
>
>

> If comparing the bow-mounted with the aft-mounted wing, in aerodynamic
>
> terms there's no advantage for the bow-mounting. ..By contrast, a racing shell typically experiences

>
> winds of around M 0.025.
>
>
> Because bow wing stays must be longer than aft wing stays, for equal
> design specifications the bow wing must offer more surface area to the
> flow & thus have somewhat greater wind drag.
>
FWIW - the stiffness demands imposed by the longer bow-wing stay
> (stiffness is inversely proportional the the cube of stay length at the
> same cross-sectional shape) have been seen in the large diameter of
> plain tubular bow wings.
>

l
If I take the example of my former FD single, the main tube of the bow-mounted rigger was in the same ball-park as the section of a blade shaft. This is relevant regarding the following.

Carl - you were (IIRC - please correct otherwise) my understanding is that you were significantly involved with the the GB rowing set-up involved with the M8+ at Sydney, a games where there was substantial concern about the aerodynamics of crews owing to the windy nature of the rowing venue - and, if I am also recalling correctly, for once there was a cogent attempt to have some rational engineering (rather than marketing-driven) thought behind the equipment that was being used.

Apart from your contribution(s) to the directional stability of the boat below the water and the rigging, weren't there also other attempts to reduce aerodynamic drag of the equipment - clothing, wind-deflectors at the front of the boat, and anti-drag 'vortex' strips on the blade shafts?

My reason for asking this is whether there would be any rationale for using similar strips or equivalent aerodynamic devices on the new-style of thicker section tubular rigging, even though they are only moving at the same velocity as the shell rather than the combination of boat speed and 'recovery speed' that would be typical for oar shafts in the air. I'm not really talking about a single scull here, either : rather a bigger sweep boat with commensurately more and heavier-duty rigger components.

[Carl]

Robin -
There's always sense in applying wind-drag reduction methods where
feasible. Winning races is not just about who pulls hardest, but
ultimately who has the highest ratio of useful power to overall drag.

One has (IMHO) to be slightly soft in the head to willingly expend
excessive energy because one is rowing inefficiently & one's equipment
incurs more wind & water drag than it need do. Yet, for almost every
crew, quite reasonable means of drag reduction are either spurned or
simply not researched or known about.

The areas where reductions in wind drag can be made include oars,
rigging, body & boat. The biggest savings in water drag, short of
radical hull redesign, will come in reducing surge, in ensuring the boat
always points the way it's going, in eliminating the parasitic drag due
to inefficient fin/rudder combinations & in reducing the leeway drag
which normally (but _not_ necessarily) arises from hull side-slip each
time there's any change, small or large, in course direction.

Improvements in useful power (without changing the athletes!) will come
from their applying blade techniques which, by reducing the amount of
turbulence, aeration & blade-slip in each stroke, waste less energy in
generating useless turbulence. Note that the puddle contains all the
work you did which did _not_ move the boat.

There are ways & means of achieving all of these things, but rowing is
largely blind to them. Good sailors fully appreciate the crucial
significance of maximising their boats' power-to-drag ratio (a fair bit
of which depends on how they sail them) & mug up on the relevant
sciences. Good rowers obsess about which hull or blades they think are
"faster", then focus on pulling harder (which is fair) & on a stylistic
thing we call "technique" - which seems to have at best only slight
relevance to real fluid dynamic theory & practice.

[thomas....@googlemail.com]

Just to update, I spoke to Row360 and they've tweaked it so it is now viewable on iOS devices

[wmar...@gmail.com]

Kind of annoying that all you get to see is the essentially the cover, some adverts, and the index, none of which have "content"... I'd rather review a few bits of "content" before deciding whether to fork out a wad of gbp..

[Leo]

On Wednesday, 24 September 2014 20:11:29 UTC+9:30, thomas....@googlemail.com wrote:
> I was given a copy of the new Row360 magazine along with a new set of Crokers M39's that I bought this week and thought i would just post here to thank Carl for his article on the science behind boats and the fluid dynamics of rowing. This edition was talking about several points including how wind drag can affect the boat speed (and how you can reduce it) and I am very impressed with how well the information is clearly presented and explained to a layman like myself. I definalty would recommend supporting the magazine if you're interested in some very high quality articles about all aspects of rowing and checking out the articles (also some good interviews with Dan Tapolski, Kim Crow, articles on HOCR and the world cups summaries, theres a lot of content!)
>
> You can pick up a copy here and/or take out a subscription
>
> http://www.row-360.com/subscriptions.php
>

Thanks for the interesting article, Carl!
I agree that air drag is an important component of the total drag
and deserves attention, as you pointed out. "Cavity drag" (the drag
to air flowing into the shell) is a very difficult problem and
it's great that you have drawn attention to it.

Just a quick comment...

Waves are generated by every part of the wetted hull surface.
Transverse waves are not really due to the bow wave bouncing up
and down. The waves created by the stern are also very important,
and so is their interaction with the hull waves created upstream.
A stern wave typically starts as a trough, not as a crest.

I'm not sure that an "ideal" hull length can really be inferred
from a consideration of the wavelength of the transverse waves.
At racing speeds (more correctly, Froude numbers) there is more
energy being shed into the wave wake in the form of diverging waves.
Transverse waves depend strongly on the hull length and speed, i.e.
Froude number. Diverging waves are more strongly influenced by the
hull shape.

[thomas....@googlemail.com]

> Now Carl, i just need to work out how to implement the modification to my new blades that you outlined in the article...... :)

Running on with this idea, does anyone have an idea on how you could implement the boundary-layer trip-strips on a set of blades and/or bow rigger?

I had considered using wire taped along the length of the blade/wind rigger on my fluid but wondered if the tape would be causing more disruption than the wire would be solving! :)

[gsl...@gmail.com]

For Carl or anyone else:

What are the pros and cons of rocker in the hull designs? Most boats these days seem not to have rocker.

What are the relevant parameters that effect how well a boat turns. Carl has explained his fin and canard elsewhere so no need to go into that again. I am primarily interested in singles and doubles. Some boats seem very easy to turn and others more difficult. How much is fin size and position and how much hull shape/length?

[Carl]

Hi Thomas -

I waited to see if anyone would come up with a better answer....

Simplest might be to get some wire (say 1mm diameter), tape its ends
only, & under tension, onto the shaft at +/- 70deg from what will be the
stagnation line when the oar is feathered, then mask either side. Apply
epoxy, PU mastic or other suitable glue, wipe clean & leave for the
adhesive to half-cure before carefully removing the masking tapes.

But there are lots of other ways to achieve a similar result, limited
only by the imagination & manual skills, including multiple layers of
fine-line masking tape, or making a notched tool to allow you to apply a
line of a suitable mastic or bodyfiller.

Remember to clean the oar-loom with a mild abrasive beforehand.

[marko....@gmail.com]

I work for a company that does wind tunnel testing. For transition bands we use strips of stick on 'boeing bumps'. As I am business rather than techical staff I'm not sure what heigh/size you would need for the Reynolds numbers we are talking about in rowing though!

[Carl]

Excellent, & I bet you know a man who does ;)

You can get adhesive rubber or rubber foam gasket tapes, which if 1-2mm
thick & sliced narrow enough might be quite suitable.

And how's about a golf-ball-textured film.

Enough for a Friday!

[usbrit]

> Disappointed the on line version is not iPad friendly
>
> Looks like I'll have to wait for the paper copy

now happy to confirm that the mag can be procured via pocketmags.com for the iPad

[robin_d...@hotmail.com]

>
> And how's about a golf-ball-textured film.
>
> Enough for a Friday!

Another question which has come to mind after watching the Boat Races - in proper headwind conditions, would the reduced diameter of the scull-like C2 skinny sweep shafts compared to more conventional diameter of either normal C2 or Croker sweep blades have a noticeable effect on a crew?

[Carl]

In short, yes.

For a 5cm diameter cylinder transverse to a 10m/sec air flow, the
Reynolds number is about 450. At that point the drag coefficient for a
smooth cylinder will have fallen almost to a plateau of around
1.2<Cd<1.4 & may rise only slightly as diameter, & hence Re, is reduced).

Since reduced diameter reduces frontal area, & since drag is
proportional to the product of frontal area times velocity squared,
slimmer oars should probably reduce wind drag, but not quite in direct
proportion to the diameter reduction.

That said, it is within the range 50<Re<800 that you might expect the
greatest benefit from fitting boundary layer trips as a means to
re-energise the surface flows & thus to reduce Cd by reattaching an
otherwise separating boundary layer.

For the slimmer oar you must be sure that its bending and torsional
stiffness remain within acceptable limits, but if the reality is that
you are outside the zone within which these become critical to your use
of the oar, then smaller diameter should be better.

[Paul]

then smaller diameter should be better.

$1000 question - How much better? (roughly)

[valery....@googlemail.com]

Measurements were done in 2011 in Concept2, where oar shafts were rotated on a centrifuge and air drag force was measured. An advantage of skinny shaft was calculated at 1.1 s over 2km at calm weather. At head wind 5m/s, it should be 3.7s over 2km.
However, much more speed could be lost (up 10s at no wind), if the blade is squared earlier on recovery, see http://www.biorow.com/RBN_en_2009_files/2009RowBiomNews12.pdf

[A. Dumas]

On 13/04/2015 10:17, valery....@googlemail.com wrote:
> However, much more speed could be lost (up 10s at no wind), if the
> blade is squared earlier on recovery, see
> http://www.biorow.com/RBN_en_2009_files/2009RowBiomNews12.pdf

However, earlier squaring will lead to better catches
(safer/longer/quicker/more efficient), I think. Certainly for imperfect
rowers.

[Sarah Harbour]

I think we can assume that catch speed isn't an issue for the Boat Race crews...

[Carl]

Many thanks, Valery, for the wind drag data:
If we want to win races we will overlook wind resistance at our peril.
Yet rowing as a sport seem oblivious to this, too often hiding ignorance
behind the falso claim that "It's the same for everyone". Well, yes, it
is the same - for everyone who declines to engage their brains.

In response to Ewoud:
For rowers who aspire to be the best, early squaring makes no sense
(except in strong tailwinds, of course). While squaring early may be a
handy prop for novices and average rowers, it has no place in good rowing.

In general:
Most racing entails rowing into a perceived headwind since our own speed
of movement is imposed against whatever the wind is doing. In strong
tailwinds there is a case for maximising wind drag, but overall you want
yourself, your boat and your equipment to cause the least possible wind
resistance.

Cheers -
Carl

PS Fluid dynamics should matter more to rowers.
FWIW, one of my Row360 articles explained how water accelerates
sternwards while passing around the body of the hull, which reduces its
static pressure & in turn depresses the water surface. Some photos from
this year's Boatrace show this rather well:
http://news.bbcimg.co.uk/media/images/82259000/jpg/_82259452_boat.jpg
This causes the shell to "squat", with increased hull drag which is
exacerbated if you pass over shallows
C

[A. Dumas]

Did seem to be for the Oxford bow man.

[A. Dumas]

On 13/04/2015 13:34, Carl wrote:
> For rowers who aspire to be the best, early squaring makes no sense
> (except in strong tailwinds, of course). While squaring early may be a
> handy prop for novices and average rowers, it has no place in good rowing.

You keep building, I keep coaching.

[Carl]

What sort of response is that? Patronising is what politicians, when in
a hole, do to try to win lost arguments.

Why would you suppose that I lack coaching experience, or that I spout
on what I haven't done or can't understand? Tsk!

I'd genuinely be interested to hear why you consider early squaring
beneficial, despite the considerable parasitic loss from a blade squared
early in a headwind. How can early squaring compensate for this extra
drag sufficiently to encourage the practice among top & aspiring rowers?

Cheers -
Carl

[Paul]

Awesome information - I wonder why they don't include this in their marketing?@

[James HS]

Have to agree with you Carl - I have spent all week coaching "just in time" squaring. People are a bit surprised when you parse the sentence - early square - it implies that it is EARLY - or TOO EARLY or somewhat premature.

I think that coaches legitimately ask novice rowers to square 'earlier' or more obviously until they get the hang of squaring at the optimum time for conditions and their fellow crew.

I'm afraid it is another coaching mantra that has separated from the physics of rowing - when I explain it to a perplexed crew they get it - oh, you mean I square in time to get a good catch - not early, not late, but square and in :)

Yup!


James

[Carl]

Most of us will never achieve the ideal and should not try to run before
we can walk. Many of us will go on squaring relatively early 'cos
that's the best we can do (& in a crew of average rowers this visual
signal can help coordination). So we'll pay the penalty for this in
headwinds as a precaution against perhaps making late or delayed catches.

It doesn't have to be so. The best rowers square & catch as a single
fluid action, & don't separate their catch from the recovery which leads
into it or from the stroke into which that catch leads. But so many
average rowers do separate recovery from catch & catch from stroke.

It's all part of the early learning process, the difficulties of which
encourage those who coach to break the stroke into a number of separate
pieces, each with their own name. The difficulty is that we then think
that's how it really should be & never learn, or think they should try,
to join it all up into a single action.

In that way it's like comparing the novice musician, scraping a violin &
looking for each note, with the Oistrakhs, Perlmans & Menhuins of their
day whose technique, intonation & phrasing were beyond criticism, yet
also notably different, & whose sound flowed seemingly without effort or
interruption.

[John Greenly]

On Tuesday, April 14, 2015 at 3:31:31 PM UTC-4, Carl wrote:

>
> Most of us will never achieve the ideal and should not try to run before
> we can walk. Many of us will go on squaring relatively early 'cos
> that's the best we can do (& in a crew of average rowers this visual
> signal can help coordination). So we'll pay the penalty for this in
> headwinds as a precaution against perhaps making late or delayed catches.
>
> It doesn't have to be so. The best rowers square & catch as a single
> fluid action, & don't separate their catch from the recovery which leads
> into it or from the stroke into which that catch leads. But so many
> average rowers do separate recovery from catch & catch from stroke.
>
> It's all part of the early learning process, the difficulties of which
> encourage those who coach to break the stroke into a number of separate
> pieces, each with their own name. The difficulty is that we then think
> that's how it really should be & never learn, or think they should try,
> to join it all up into a single action.
>
> In that way it's like comparing the novice musician, scraping a violin &
> looking for each note, with the Oistrakhs, Perlmans & Menhuins of their
> day whose technique, intonation & phrasing were beyond criticism, yet
> also notably different, & whose sound flowed seemingly without effort or
> interruption.
>
> Cheers -
> Carl

Ah, yes! This observation suggests the inevitable question: how, beyond raw talent, do people do this?, Well, musicians develop this "legato" - smooth, connected- playing by practicing over and over and over at a slow tempo. That's the only way. My teacher used to say that you only need to do it at full speed once- at the concert. An exaggeration, of course, but it makes the point.

But, how to do this in rowing? In music it's more or less straightforward: just play slower. but in rowing it's not so simple. Because of the steeply increasing power with the cube of speed, decreasing your power doesn't slow you down all that much, so rowing slower is not exactly a perfectly scaled-down version of rowing faster. For instance, rowing at half racing speed needs something like 1/8 the power at full speed. So, for example, if you drop the rating by half and pull just as hard, you will go much more than half speed, so the drive time will be not nearly doubled, and the recovery time will be a much larger proportion of the stroke time, changing the rhythm of the stroke. In other words, if you do the recovery at half-speed, but as the blades enter the water, which is flowing past at much more than half-speed, your motions likewise have to go faster than half-speed.

One possible solution might be to increase the drag on the boat to go slower- as with putting bungees around the hull. I feel that I can get good slow-speed practice, at least in some respects, by rowing my slower wherry instead of the racing boat.

I'm sure people have thought about this, but I've not seen it discussed here on RSR, as far as I remember. The lesson from musicians is that very slow practice works wonderfully as long as you keep the rhythm unchanged; then the brain, nerves and muscles seem to be good at simply scaling up the tempo.

Cheers,
john

[John Greenly]

On Tuesday, April 14, 2015 at 3:31:31 PM UTC-4, Carl wrote:

>

> In that way it's like comparing the novice musician, scraping a violin &
> looking for each note, with the Oistrakhs, Perlmans & Menhuins of their
> day whose technique, intonation & phrasing were beyond criticism, yet
> also notably different, & whose sound flowed seemingly without effort or
> interruption.
>
> Cheers -
> Carl

Can't resist one other comment- If you ever watched Oistrakh play something like the Sibelius concerto, you may have felt an instant of fear for that frail little violin in his hands, there was so much power there he could have crushed it into splinters, though at the same time he had absolute sensitivity and delicacy. Some of the greatest heavyweight scullers give somewhat the same impression at their best.

--John

[Carl]

Not sure I see the problem quite as you do, John?

Playing music does not demand force or sheer work in the way that rowing
does, & rowing "legato" does not demand force either. The stroke
duration can be greatly, or proportionately, extended if you reduce the
work level appropriately, despite the cube-law constraint - no one makes
you pull any faster than you wish.

So rowing offers you many ways to practice at reduced speed or at
reduced power, from just dropping your rate with or without changing
pressure to just dropping pressure with or without changing rate. And,
as in music & as you say, gentle, low-pace practice, with focus on
smoothness & the proper continuity/phrasing, is the route to
accomplished performances in concert hall or at the regatta.

I'm always depressed on hearing of youngsters being told to get strong &
fit first, & only to worry about technique after that. By the time
they're deemed adequate physical specimens their use of ergs & weights,
& their ignorance of technique & feel, may have made it impossible for
them either to enjoy the rowing experience or to develop the degree of
feel & technique which would enable them to effectively apply that power.

And to then teach rowing as a series of discrete actions & postures -
which forms part of the current UK orthodoxy - hardly helps. But what
would I know?

[John Greenly]

On Wednesday, April 15, 2015 at 2:06:45 PM UTC-4, Carl wrote:

> Not sure I see the problem quite as you do, John?
>
> Playing music does not demand force or sheer work in the way that rowing
> does, & rowing "legato" does not demand force either. The stroke
> duration can be greatly, or proportionately, extended if you reduce the
> work level appropriately, despite the cube-law constraint - no one makes
> you pull any faster than you wish.
>
> So rowing offers you many ways to practice at reduced speed or at
> reduced power, from just dropping your rate with or without changing
> pressure to just dropping pressure with or without changing rate. And,
> as in music & as you say, gentle, low-pace practice, with focus on
> smoothness & the proper continuity/phrasing, is the route to
> accomplished performances in concert hall or at the regatta.
>
> I'm always depressed on hearing of youngsters being told to get strong &
> fit first, & only to worry about technique after that. By the time
> they're deemed adequate physical specimens their use of ergs & weights,
> & their ignorance of technique & feel, may have made it impossible for
> them either to enjoy the rowing experience or to develop the degree of
> feel & technique which would enable them to effectively apply that power.
>
> And to then teach rowing as a series of discrete actions & postures -
> which forms part of the current UK orthodoxy - hardly helps. But what
> would I know?

Yup, that all seems just right to me. So, if I want to practice at half-speed, that is, slow everything down so it would look like playing a video at half-speed, then all my motions, and the speed of the water past the hull, will be at half-speed. That would mean that I would be pulling with 1/4 of the force I use at full speed. (Power is down by 1/8, but speed is also halved). I'll try this. Generally when I practice at low rate I still pull hard, which distorts the rhythm as I wrote, and doesn't allow the motion through the catch to get slowed down as much as i want.

It is indeed a problem in rowing training that one can't practice slowly and still get the strength and fitness work done at the same time, at least not in a racing boat. If you row a boat with a lot more drag, then you can both move slower for good technique practice and get a good workout at the same time. I do think I will try bungees around the hull.

Cheers,
John

[Carl]

I think one should separate some aspects of technique improvement from
the "get fit" part of one's training.

Too often rowers equate pressure with rate but, as we've discussed here
before, there is no logical connection. Indeed that way madness lies,
often in the form of injunctions to "get rate up through the water"
which totally disregard the iron limits imposed on rowers by the inverse
cube law. And for those (not John!) who may be confused by that
reference, I mean that:
boat speed is proportional to the cube root of your power output

To row well we need to build dexterity, rhythm, coordination & all the
non-violent aspects of the rowing process. Many of us can best solve
those puzzles by practising at combined low rate & low pressure before,
at a later time, working to raise pressure, rate or both without losing
what we had gained.

If, just to slow the power stroke, you apply a hull resistance then you
are sustaining the work rate while completely changing the stroke rhythm
into something you'd never experience under normal conditions. Of
course resistance training can play an important part in the overall
training scheme, but it so changes the stroke dynamics that it is most
unlikely to help you to resolve the finer aspects of your technique. I
suppose a musical parallel might, to some degree, be expecting a
trumpeter or pianist to play fortissimo while simultaneously trying, by
playing legato, to smooth their technique? Yes, there might be a time
for that too, but probably only as an add-on for some limited, specific
purpose.

[John Greenly]

Yes, this is great! I was thinking about that too. For the musician, tempo (speed) and dynamic (loudness, or pressure) are two independent variables. We certainly do not generally couple them so that when we practice slowly we also play very softly (unlike slowing down the boat in rowing practice, which requires dropping the pressure way down). As Carl well knows, instruments respond quite differently at fortissimo and pianissimo levels, so when we practice a passage very slowly, we would typically not scale down the loudness, but rather would play at the proper performance dynamic. Take, for instance, a pianist practicing a Rachmaninoff concerto, which does in fact require immense physical strength. She could certainly practice it softly as well as slowly at first, but then would bring the dynamic up to performance level- playing those gigantic chords at full pressure- while still at slow tempo, and then finally work the tempo up to performance level. That full-pressure-slow-speed stage of practicing is the one that is not easily available in rowing training, because of the coupling of boat speed to the pressure on the oars-- that's what I have been wondering about.

Or... maybe I'm wrong: for the pianist, there is a complicated muscular thing going on. To play fortissimo, she needs to use full pressure and speed to strike the keys, but at slow tempo she can take her time, move slowly and gently, to get from one chord position to prepare for the next chord. Maybe that is a lot like rowing at very low rate but high pressure- you move slowly on the recovery, but then the catch still has to be quick since you have to match the speed of the water moving past the hull. Maybe it's okay for effective training that the only way to substantially slow down the catch for practice is to also drop the pressure way down to slow the boat?

Now then, ignoring the "get fit" part, what I am thinking about adding a lot of resistance is something like this: suppose you add a lot of drag so that the boat slows down rapidly during the recovery. Then you could choose your rate so that you get to the catch as the boat speed drops to, say, 1/2 or 1/4 speed, and thereby allow the catch itself to slow down that much while still pulling hard. You could do the same without the extra drag, of course, but you'd have to wait a very long time to get down to the slow speed.
I think I'll try it out this weekend and see how it works.

Cheers,
John

[gsl...@gmail.com]

1) Rowing with a bungee is a standard training method but you have to watch out for two things:
a) it dramatically increases the load at the catch. You need to be careful you don't hurt your back as a result. So don't use it for very long, say 10 minutes, at first--tie to the riggers so you can remove it without docking.
b) the rhythm is quite a bit different and for some people (certainly not all) it can hinder technique.

You can row slowly and get a good workout. Many (most?) coaches recommend steady state workouts at about 16-18 spm, and about half the 2K power output. This means the handle force is the same as it is at race pace, but since it happens half as often the power is cut in half. This is the bread and butter of most elite athletes training. The boat would be moving about 20% slower so the catch is only 20% slower, but the recovery time is about doubled. This gives you plenty of time to think and prepare for the catch. (You can lower the rating even more if you need more time, but then you much have that much better balance, slightly drag your oars, or use a more stable boat).
There is no need to use a bungee to get a good workout at slow speed, but they do provide a good way to training increased force. Given the number of top rowers who rarely use one, clearly they are not necessary to use often.
That said I have used bungees extensively at various points.

[2potsin...@gmail.com]

I am going to pop in from my usual lurk-mode, both to say again how much I enjoy and benefit from reading all your collective wisdom (and particularly Carl), and also add my small 2 cents to this topic. My rowing clubs are on a fairly long (13 miles) very sheltered public water supply reservoir, so we row hard and fast when we want to, but the water conditions (flow, wind and waves, other boat traffic) are rarely a problem. One practice last year, we were at our farthest usual distance from the boathouse when the coach's launch developed an engine problem. There was no one else nearby, so the coxswain took the launch tie-up rope in hand and we towed the launch 6 miles back to the dock. I cannot recall a better practice - we were able to put full effort into long steady rowing that was slow enough through all phases of the stroke that we were also able to work on fine-tuning some technical issues we were having. And the coach appreciated being a mere few feet astern of the shell and not having to shout over the din of the engine.

Back to lurk-mode

Dick White, in sunny Virginia where it is finally warm enough to row again.

[John Greenly]

On Thursday, April 16, 2015 at 1:33:22 PM UTC-4, gsl...@gmail.com wrote:
> 1) Rowing with a bungee is a standard training method but you have to watch out for two things:
> a) it dramatically increases the load at the catch. You need to be careful you don't hurt your back as a result. So don't use it for very long, say 10 minutes, at first--tie to the riggers so you can remove it without docking.
> b) the rhythm is quite a bit different and for some people (certainly not all) it can hinder technique.
>
> You can row slowly and get a good workout. Many (most?) coaches recommend steady state workouts at about 16-18 spm, and about half the 2K power output. This means the handle force is the same as it is at race pace, but since it happens half as often the power is cut in half. This is the bread and butter of most elite athletes training. The boat would be moving about 20% slower so the catch is only 20% slower, but the recovery time is about doubled. This gives you plenty of time to think and prepare for the catch. (You can lower the rating even more if you need more time, but then you much have that much better balance, slightly drag your oars, or use a more stable boat).
> There is no need to use a bungee to get a good workout at slow speed, but they do provide a good way to training increased force. Given the number of top rowers who rarely use one, clearly they are not necessary to use often.
> That said I have used bungees extensively at various points.

Thanks! Yes, certainly I do a large part of my work in the 18spm, more or less full pressure regime, and the doubled recovery time is very good as you say. As you point out, though, that doesn't allow the catch to slow down very much. Musicians like to learn new motions at very much reduced speeds, 1/2 or even much less, and that's what I'm thinking about.

Thanks very much for the cautions about bungee rowing. I would not be trying to use it to increase force, but just to slow me down a lot at moderate force, and I wonder if that might mitigate the problems you mention?

--John

[John Greenly]

Dick,

thanks for un-lurking! This is a very interesting example. I wonder- you added not just resistance but also mass (inertia) and that may have helped even out your speed and made the practice work out better. I'm curious though, I remember trying to tow a very heavy sailboat with a light rowing dinghy, and the nonsteady nature of rowing- backwards pull from the tow during the drive, then no pull during the recovery- made it a lurching, frustrating and ineffective effort. Maybe you were in an eight, and the launch was lighter than your boat and crew?

--John

[John Greenly]

On Thursday, April 16, 2015 at 5:08:32 PM UTC-4, John Greenly wrote:
> On Thursday, April 16, 2015 at 2:10:58 PM UTC-4, 2potsin...@gmail.com wrote:
> > I am going to pop in from my usual lurk-mode, both to say again how much I enjoy and benefit from reading all your collective wisdom (and particularly Carl), and also add my small 2 cents to this topic. My rowing clubs are on a fairly long (13 miles) very sheltered public water supply reservoir, so we row hard and fast when we want to, but the water conditions (flow, wind and waves, other boat traffic) are rarely a problem. One practice last year, we were at our farthest usual distance from the boathouse when the coach's launch developed an engine problem. There was no one else nearby, so the coxswain took the launch tie-up rope in hand and we towed the launch 6 miles back to the dock. I cannot recall a better practice - we were able to put full effort into long steady rowing that was slow enough through all phases of the stroke that we were also able to work on fine-tuning some technical issues we were having. And the coach appreciated being a mere few feet astern of the shell and not having to shout over the din of the engine.
> >
> > Back to lurk-mode
> >
> > Dick White, in sunny Virginia where it is finally warm enough to row again.
>
> Dick,
>
> thanks for un-lurking! This is a very interesting example. I wonder- you added not just resistance but also mass (inertia) and that may have helped even out your speed and made the practice work out better.

> --John

Hey, yes, that's it! I should have realized this. To row slowly with the same pressure, so that all motions are slowed like a slow-mo video, the mass needs to change.

I should have realized this because a standard technique in physics to understand how some phenomenon scales with changes in parameters is dimensional analysis and the construction of dimensionless numbers to characterize the scaling, as for instance the many dimensionless numbers of fluid mechanics like Reynolds number, Mach number, Froude number, etc.

I want to keep the force, or pressure, constant and change the speed, so all quantities have to be transformed into units of force and made dimensionless by dividing by a reference value of force. That means acceleration must be multiplied by mass to put it into units of force.

Think about what happens as you slow down the video by a factor of two. The drive lasts twice as long, but the change in speed during that doubled time is only half as much as normal. That means the acceleration is reduced by a factor of 4. However, the driving force is unchanged, so we need to increase the mass by a factor of 4 to keep the product of mass and acceleration constant.
The drag force must also be held constant, and to have the same drag force at half the speed, we do need to add resistance to the hull (maybe a bungee?). Again, with the unchanged drag force and 4 times the mass, the accelerations during the recovery will be properly scaled down.

Strictly speaking, all parts of the system, the rower(s) and the boat, should have their masses quadrupled, but that obviously isn't practical, (among other things, certain sink-like-a-stone qualities would result). Anyway, the rower can slow down his internal motions as he wishes; the internal inertial forces will decrease greatly out of proportion, but maybe that's not too important to the feel of the practice. So, both extra mass and extra resistance must be added to the boat to allow an nearly unchanged rhythm at slower speed but full pressure, and I think that's what Dick White's experience tells us. And that's why just adding a bungee messes up the rhythm as has been stated.

And indeed, towing a suitable object, like a coach and his launch, might be a more practical way to do it than adding a lot of mass to the boat itself. But I know that wouldn't work in a single because of the lurch factor as I described. So a substantially heavier boat, like my wherry with some extra weight added, might do the trick.

Technical detail:

In the hypothetical slowed video, the dimension of length L is invariant: the boat (and everything else too, like how far it travels during the drive) doesn't get shorter or longer. So velocity V can be made dimensionless as [(mV^2)/L]/Fref, where m is mass and Fref is the reference force. So again, half speed means 4 times the mass to give the same dimensionless quantity. This scaling also makes the kinetic energy invariant, as it must be with invariant force and distance, that is, work done.

Is all this correct? I'm writing it on the fly, but I think so.

Cheers,
John

[2potsin...@gmail.com]

On Thursday, April 16, 2015 at 5:08:32 PM UTC-4, John Greenly wrote:

Yes, we were in an eight, and the launch was an aluminum v-hull, maybe 14-16', 9.9hp motor, normal size coach. Can't do the math on change in mass as I don't have factual details for the launch, but surely the relationship between the shell and the launch was not inverse to the extreme as your experience with the dinghy vs. sailboat. I would be leery of trying to safely and correctly row with that much added mass directly in/on the shell (would be hellacious trying maintain set if the shell had that much mass), but I noticed that tension on the tie-up rope pulled by the coxswain was fairly constant through the stroke, indicating that the water resistance on the launch was enough to slow it's forward speed even as our forward speed decreased for whatever reason. It was nothing like the infamous MythBusters episode where the UW varsity crew pulled up a water skier, but the skier could hardly stay upright with the oscillation of the tow rope. If I were a coach, I might develop a drill or whole workout around towing a launch.

[John Greenly]

On Thursday, April 16, 2015 at 11:10:42 PM UTC-4, 2potsin...@gmail.com wrote:

> Yes, we were in an eight, and the launch was an aluminum v-hull, maybe 14-16', 9.9hp motor, normal size coach. Can't do the math on change in mass as I don't have factual details for the launch, but surely the relationship between the shell and the launch was not inverse to the extreme as your experience with the dinghy vs. sailboat. I would be leery of trying to safely and correctly row with that much added mass directly in/on the shell (would be hellacious trying maintain set if the shell had that much mass), but I noticed that tension on the tie-up rope pulled by the coxswain was fairly constant through the stroke, indicating that the water resistance on the launch was enough to slow it's forward speed even as our forward speed decreased for whatever reason. It was nothing like the infamous MythBusters episode where the UW varsity crew pulled up a water skier, but the skier could hardly stay upright with the oscillation of the tow rope. If I were a coach, I might develop a drill or whole workout around towing a launch.

Excellent observations! The key is that, as you suggested, the mass and drag must have been right so that the launch followed the oscillating towing force smoothly. It seems as if it might be possible to design a suitable tow for a single. Quadrupling the mass is probably way too much, but a lesser mass with the right extra resistance might work. Possibly an old sailboard suitably loaded...? Experiment time!

thanks!
John

[Matthew Farrow]

Hi Carl,

I appreciate I am very late to the thread but I am currently doing some research on the topic and have a couple of enquiries.

If this finds you, please can you explain how you got these values for Reynolds numbers?

Transition from laminar to turbulent for a smooth cylinder happens at Reynolds numbers in the region of 200,000 (see Fundamentals of Fluid Mechanics, p501, http://civilcafe.weebly.com/uploads/2/8/9/8/28985467/fluid_mechanics.pdf). Personally, I calculated the Reynolds number of the cylinder in conditions you described to be around 32,000, much higher than your value of 450. Some discussion on this would be great :)

Matt