Rowing in another boats slipstream/puddles

[Paul]

Is there a speed advantage from rowing in another boats slipstream?

Alternatively, if you are the lead boat can you slow the boat behind you by forcing them to row in your puddles?

[SingleMinded]

On Thursday, 29 November 2012 21:16:15 UTC, Paul wrote:
> Is there a speed advantage from rowing in another boats slipstream?
>
>
>
> Alternatively, if you are the lead boat can you slow the boat behind you by forcing them to row in your puddles?

It slows you down- in Bumps racing, gaining the last half length to make the bump is significantly harder than gaining the length before. Some of that, I agree, is due to desperation making the crew ahead push harder, but the bumpy water behind them certainly does have an effect.

For similar reasons, the bump to headship is considered harder because the crew at the front of the division has smooth water to row in, while everyone else is (to a varying extent) rowing in water churned up by the crews in front. "Headship advantage" is usually agreed to be worth about 1 1/2 lengths over the 2.7k Cambridge course.

[sully]

On Thursday, November 29, 2012 1:16:15 PM UTC-8, Paul wrote:
> Is there a speed advantage from rowing in another boats slipstream?
>
>
>
> Alternatively, if you are the lead boat can you slow the boat behind you by forcing them to row in your puddles?

I've tried in my single, couldn't make it work. The reason I've tried is because a K-1 can definitely get slip help behind a single, so I figured a single could as well. A K-1 used to train with me at times, and when I learned to paddle myself, also tried it to positive effect. It's simply easier to stay close in the slipstream in a K-1 than in a single, and my observation is that you need to be no further than about 1-2 feet from the stern to feel the diff.

Else, I do think putting someone in your wake and puddles is an advantage, yes.

[Carl]

Flat-water kayakers like to wash-hang the guy in front.

Kayaks put more energy into their following wave patterns than rowing
shells do, & it's easy for the guy behind to "get onto" & ride the
leader's wake - a bit like very low-grade surfing.

It's one reason why you find kayakers in the wrong place on the river.
The leader is trying to wipe off the wash-hangers while the wash-hangers
try as far as possible to follow him.

Not easily done in rowing or sculling, even in a 1x.

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...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: carldouglas.co.uk & now on Facebook @ CarlDouglasRacingShells

[sully]

On Thursday, November 29, 2012 6:24:40 PM UTC-8, Carl wrote:
> On 30/11/2012 00:42, sully wrote:
>
> > On Thursday, November 29, 2012 1:16:15 PM UTC-8, Paul wrote:
>
> >> Is there a speed advantage from rowing in another boats slipstream?
>
> >>
>
> >>
>
> >>
>
> >> Alternatively, if you are the lead boat can you slow the boat behind you by forcing them to row in your puddles?
>
> >
>
> > I've tried in my single, couldn't make it work. The reason I've tried is because a K-1 can definitely get slip help behind a single, so I figured a single could as well. A K-1 used to train with me at times, and when I learned to paddle myself, also tried it to positive effect. It's simply easier to stay close in the slipstream in a K-1 than in a single, and my observation is that you need to be no further than about 1-2 feet from the stern to feel the diff.
>
> >
>
> > Else, I do think putting someone in your wake and puddles is an advantage, yes.
>
> >
>
>
>
> Flat-water kayakers like to wash-hang the guy in front.
>
>
>
> Kayaks put more energy into their following wave patterns than rowing
>
> shells do, & it's easy for the guy behind to "get onto" & ride the
>
> leader's wake - a bit like very low-grade surfing.
>
>
>
> It's one reason why you find kayakers in the wrong place on the river.
>
> The leader is trying to wipe off the wash-hangers while the wash-hangers
>
> try as far as possible to follow him.

This has been a subject of debate in our areas, course rules in rowing vs paddling. I have been advocating that paddlers need not, nor should not follow our rowing course rules, but follow standard rules of taking best course and passing oncoming traffic to port.

because the outriggers/ surfskis, etc are generally slower than the shells, it would be otherwise tricky for a blind boat to bow to pass a blind boat to stern.

>
>
>
> Not easily done in rowing or sculling, even in a 1x.

I'm a terrible k-1 paddler and once was a decent sculler. I could never make it work in a single, even when two of us were playing around TRYING to make it work, but can readily do it in a K-1.

kudos to the sculler that can!

the problem was making the minor adjustments to course necessary to stay centered in the draft flow. maybe a bow coxed boat could do it?

Carl, does this make sense that the trailing bow needs to be no more than a couple feet from the stern, anything farther back gets no help? That's been my experience watching yakkers draft me, and trying myself.

follow up: does drafting affect the drafted boat? I never thought so, but maybe that's a poor assumption. I certainly never felt it when being drafted.

[Carl]

This is really one for Leo Lazauskas, who knows most everything you'd
need to know about the interactions between moving hulls. You there, Leo?

Everything moving through a fluid creates a pressure & flow field around
itself. Or how would, e.g., water know how to part & move around
whatever's moving through it?

Anything moving at or close to the interface between 2 separate fluids
(e.g. air & water) also generates cyclic oscillations in the fluids
relatively close to that interface - we call 'em waves - because the
surface is only held flat by gravity & quite small pressure changes have
noticeable effects on water surface levels (ask those affected by
tropical storm, earlier hurricane, Sandy). Those waves take energy away
which can be used by others, as in wash-hanging.

And anything sitting on a nearby wave must itself generate its own
pattern of waves & pressure fields, etc., even as it gains energy by
being able to surf that wave. So I suppose a wash-hanger might affect
the progress of the boat in front, e.g. by interfering with the
processes of pressure recovery in the flows slowing & coming back
together (& their streamlines thus spreading apart) near the leader's
stern, & also by changing local surface levels there.

I suspect it's mostly going to have a marginal effect, which at times
might even be helpful & at others a hindrance - but ask Leo.

When 2 hulls are moving side-by-side that can have a significantly
unhelpful effect on both as flow funnels slightly between them (which
can cause the boats to pull towards each other too). You get a similar
sideways-sucking effect if you take a moving hull relatively close to
say an embankment wall, & again hulls can "squat" when passing over
shallows, even striking the bottom despite chart indications that they
should have had enough depth.

[Sarah Harbour]

I've tailgated 8s on the Cam before when I've set off behind them and expected them to move away from me, and then they just haven't. I don't know whether that is a combination of the crew not being as fast as I expected, or me just having a patch of really good sculling, but last time I mentioned this on here it was suggested that I was wash-hanging!

Sarah

[Sarah Harbour]

And I meant to add, that I could believe that it's easier for a single to do this to an VIII becuase of the relative widths of the boats - if you get close enough to the stern, you're not really affected by the puddles as they just go past on either side.

[Leo]

Well explained, Carl!

There is almost no chance of gaining an advantage by wave
cancellation in rowing because the optimum location of the aftmost
vessel is speed dependent (technically, Froude number dependent).
A crew would have to very carefully position itself behind and to
the side of the lead vessel.

It is possible in kayaking because these vessels tend to have much
less speed variation during a stroke.

In most cases (excepting windy conditions) it's best to lead
throughout the race and, if possible, accelerate over the last 250
meters.

[Carl]

A 1x generates a relatively light swell &, being longer & thinner than a
kayak, it is harder to wash-hang it behind another 1x. An eight is a
different proposition: it displaces the better part of 1 tonne & its
passage has a big effect on nearby flows & levels.

I agree it may also be easier to tuck in behind an eight &, with so much
wave energy being trailed behind it, in a 1x you've a good chance of
getting onto a wave & staying there.

This is even more true on a narrow, shallow river like the Cam, where
you row Sarah. As I noted previously, the close-by river bed & banks
reflect & may amplify the eight's pressure & flow fields. That some
college eights are pretty slow won't hurt either!

Now a question:
Why aren't these relatively straightforward fluid-dynamics questions
being explained for us by the boffins at that nearby university, instead
being left for answers from some racing shell designer & builder? Isn't
it common knowledge that boat-builders are uneducated chaps who know
nothing except how to doff their caps?

I put a fair bit of my unpaid effort into trying to widen rowers' grasp
of what really happens when they pull on those oars & get all sweaty.
So I'm amazed that rowers take so little interest in things which, if
they understood them better, would make the intelligent ones faster.
And I'm not a little disappointed to receive few questions & fewer
challenges. It's as if rowers find it too much to ask of them to
combine thinking with training.

By applying fluid dynamics, sailors can build boats which have now
reached 120km/hr (that's several times true wind speed!). How do they
do that? Similarly, the unofficial record for ice yachts stands at
around 225km/hr - in even less wind. And the new America's Cup
72-footer cats have been clocked at over 80km/hr. None of which would
be possible if sailing technology was run by rowers!

My firm makes advanced steering accessories (among other things).
That's because I've a fluid-dynamics background & improving shell
performance really interests me. So it bugs me that I encounter so many
blinkered responses when introducing rowers to our well-designed
steering foils, & near incredulity towards our even more efficient
HyperSteer twin-foil shell control system:
http://www.carldouglas.co.uk/downloads/HyperSteer 3.gif

Responses range from "you're increasing drag by adding a foil to the
bottom of the boat" (no, it doesn't!), & "surely" that for'd foil must
"make the boat unsteerable" (who thinks an eight's bow is steered by a
rudder at the stern?). The peach was a Dutch coach who, told our
steering foil alone could save his crew a couple of seconds on a
straight course, answered triumphantly, "well, my crew could pull 2
seconds faster". Doh!

Then come comments based on cost. One coach said he was sure our
steering foil would improve boat speed but they wouldn't fit one as it
would cost more to replace than his inefficient plate fin/rudder kit if
he knocked it out. I explained they were much tougher & harder to lose,
then asked what it cost to lose by 1/2 length a race you'd otherwise
have won? Finally I asked, if his crew broke a blade, did they pull an
old wooden oar off the clubroom wall to save money? No, he replied, we
always buy 10 blades to cover for breakages! So they lock up several
times the price of the foil they won't lose & that _will_ improve their
performance to have cover for blades they will break, & with no evidence
that the blades they prefer can make them the slightest bit faster.

Am I banging my head against a brick wall?

[James HS]

It does surprise me because the athletes will happily spend £££ on kit and sports drinks if they think it will make them go faster!

[Jonny]

On Dec 2, 12:10 am, Carl <s...@sss.jjj> wrote:


>
> Am I banging my head against a brick wall?
>

Yes.

Next question?

[Phil]

I know of no other sport where innovation is effectively legislated
against. There lies one root of the problem....


Phil.

[SingleMinded]

Cycling? While there is innovation, a lot of advances have been stopped by the UCI.

Also swimming with the recent restriction on skinsuits, Olympic archery (compound bows are banned), etc...

I think some restriction of completely game-changing innovations is necessary, especially in a sport like rowing where clubs have a huge amount of money sunk into equipment that could be rendered obsolete overnight. For example, the reason I've heard for the ban on sliding riggers is that sliding-seat boats couldn't compete with them and can't (as far as I know) be converted, so clubs would have had to either replace their fleets at huge cost or be rendered uncompetitive. The same might apply to hydrofoils if anyone ever got one to work reliably and they hadn't been preemptively banned.

The alternative would be to slowly phase in a new technology, as happened with sliding seats and shell boats in Oxbridge college racing- the new technology was allowed at the higher levels first, sometimes resulting in the weird situation of a crew being promoted to a division that allowed sliding seats and having one outing to get used to them before having to race with them! This would result in practical difficulties and I'm not sure if it's desirable as it would relegate poorer clubs to competing at a lower level until they can replace their boats, but it's better than unrestricted introduction.

Of course, there's no problem with a technology that's either less game-changing or cheaper to introduce. I wonder what the problem was with riblets...

[Carl]

On 04/12/2012 11:43, SingleMinded wrote:
> On Tuesday, 4 December 2012 10:40:34 UTC, Phil wrote:

<snipped>>

>>
>>
>> I know of no other sport where innovation is effectively legislated
>>
>> against. There lies one root of the problem....
>>
>>
>>
>>
>>
>> Phil.
>
> Cycling? While there is innovation, a lot of advances have been stopped by the UCI.
>
> Also swimming with the recent restriction on skinsuits, Olympic archery (compound bows are banned), etc...
>
> I think some restriction of completely game-changing innovations is necessary, especially in a sport like rowing where clubs have a huge amount of money sunk into equipment that could be rendered obsolete overnight. For example, the reason I've heard for the ban on sliding riggers is that sliding-seat boats couldn't compete with them and can't (as far as I know) be converted, so clubs would have had to either replace their fleets at huge cost or be rendered uncompetitive. The same might apply to hydrofoils if anyone ever got one to work reliably and they hadn't been preemptively banned.
>
> The alternative would be to slowly phase in a new technology, as happened with sliding seats and shell boats in Oxbridge college racing- the new technology was allowed at the higher levels first, sometimes resulting in the weird situation of a crew being promoted to a division that allowed sliding seats and having one outing to get used to them before having to race with them! This would result in practical difficulties and I'm not sure if it's desirable as it would relegate poorer clubs to competing at a lower level until they can replace their boats, but it's better than unrestricted introduction.
>
> Of course, there's no problem with a technology that's either less game-changing or cheaper to introduce. I wonder what the problem was with riblets...
>

Yes, cycling has a lot to answer for. No restrictions on materials, so
cost can soar, but restrictions on design, so the sport's evolution is
stifled. When a sport is ruled by old folk of sometimes questionable
integrity, as are so many, that's no recipe for any sport's healthy
development. And sponsorship pressures in such a setting only make
things worse.

One popular myth around cycling is that the so-called Lotus bike used to
win gold by Chris Boardman, & subsequently outlawed by those who love to
make rules, was a much faster machine. No, it wasn't. Actually it
seemed to have no aerodynamic advantage but in wind-tunnel testing of
the bike a riding positions was found which was better than more usual
positions, & there was too much publicity about the myth of the machine
to cast it aside. The winner was the fantastic cyclist, not the bike.

And when it comes to dumb-arsed official reaction to an athlete's
intelligent adjustment of man & machine to the laws of aerodynamics you
have only to consider the travails of Graeme Obree. And what do we
still keep hearing about his bikes? That he used a washing machine
bearing! How shallow & irrelevant is that?

The sliding rigger example which you quote, as do so many others, is
invalid. It's merely a modern myth - an ex-parrot, if I may put it
thus. There is zero statistical evidence in regatta records to sustain
the popular belief that sliding rigger shells went faster than fixed
rigger boats and were cynically killed off therefore. People love the
idea of a great innovation killed off by cynical officialdom. It's
easier to repeat unfounded rumour than to check the plain facts, & when
a myth gains powerful currency through ill-informed repetition it's
unsurprising that it comes to be taken as the gospel truth.

I am against changes which radically alter what we do "to row", or which
may price people out of our sport. So I don't favour hydro-foiling
shells - except as a completely different class (which I would favour).
On that same basis I regret the transfer of rowing from rivers to
multi-lane courses, which has increased competition costs, created
greater unfairness, reduced competitions to "the same old same old"
(Wallingford @ Dorney, Marlow @ Dorney, The Met @ Dorney, etc.) for the
greater benefit of the owners of such facilities, & encouraged the
disease of points avoidance.

I do favour simple, intelligent modification of shells to make them more
fit for purpose, but not the uncritical changing of kit driven by
implausible promises or slavish imitation. Look critically at oar
developments: there is scant evidence that a Hatchet, used as currently
coached, is a better boat-mover than a Macon. There is, however, solid
theory & demonstrable fact to show that an oar used a little differently
than currently coached can move you faster. And there's far too much
evidence of minds closing when confronted by this possibility.

I see only general benefit in providing shells with much better steering
systems by applying science to the job rather than ignorance. Why have
a very expensive eight held back by the folly of expecting the little
person to steer it with 20 quids' worth of flat tin plates? What's the
sense in all those shells, in the cross-wind Oly finals, going sideways
& slowly down the course, with those in the windier lanes going even
more sideways & thus even slower?

Was that about level playing fields & fair competition? No, it was
ignorance when, for less than the cost of 1 fancy oar, any of those
crews could have travelled straighter & thus faster.

In the same regatta, with little expectation of significant headwinds, a
few crews sported expensive cowls on the decks ahead of the bowman -
designed by McLarens, the F1 boys, to reduce the non-existent windage.
I know at least 1 boat-builder with costly a hire fleet at the event had
to carry a valuable stock of such kit just to ensure the so-called level
playing field, but most crews sensibly chose not to bother.

(Funnily enough, in 1988 we supplied a similar aerodynamic cowl for a
crew in the Worlds on windy old Lake Karapiro. Did they use it? Did
they heck, & they had no explanation for why they left it in the box,
beyond fear of doing something unusual - like a GBR women's crew using a
bit of wit to help them beat the E. Germans!)

And that's my point. Rowing is expensive at the top - in the boats it
uses or hires, in travel & accommodation costs & the palaver of its
major events. But the cost of extracting real performance improvements
from this & similar kit, through applying a better understanding of the
relevant inertial & fluid dynamics, is truly minute. Rowing so little
understands this, & is so smug in its unfounded theories of boat
propulsion, & so naive on boat design, so determined not to engage with
the necessary sciences, that it buries its head in the sands of "pull
harder".

British Cycling did it so much better. It had a stated policy of "the
aggregation of marginal gains". Everything was tried and tested.
Anything that gave advantage was implemented. Anything which slowed
things down was ditched. There were no sacred cows. A few milliseconds
saved here, a few more there - were all added together into real
performance improvements. That's what I call smart.

Rowing is too much about hierarchies, personalities & control, too
little about science, & maybe sometimes too little about humanity: "He
says do it this way, that boats of that colour must be faster, that we
don't talk to him, stay orthodox & discourage diversity, don't embrace
the expertise of others, keep it all the same &, at all costs, under
control." Thus it closes its collective mind to the available
technology, chances to do better.

That may seem harsh criticism. Unfortunately my long experience of this
and other sports tells me it is far from untrue.

[Carl]

On 04/12/2012 15:32, Carl wrote:

PS What was the problem with Riblets™?

The problem was the cost of applying them in the adhesive tape form
available from 3M. That could certainly have been overcome, & similar
textures could have been imprinted at the moulding stage.

That said, there was a distinct shortage of evidence from rowing, & none
published at or since the time of their banning. There was a lot of
rumour, which was as far as it got.

Such rules are often made up as knee-jerk reactions, to block what
administrators most fear - the game running away from them.

It was the same with boat weight rules. There are no valid grounds to
think a lighter boat is always or ever a faster one, but solid practical
& theoretical evidence to show that, at typical boat weights, the odd
kilogram one way or t'other is not important to performance (sorry to
explode another fine fiction). But FISA's fear of an "arms war" drove
their creation of boat weight rules which saddle tiny girls with the
same minimum weight of boat as huge male gorillas. I rest my case!