It has been stated or implied by many dragonboaters that the lead boat is slowed down by other boats riding their wash (side wash). In marathon canoes, wash riding is a accepted and respected and oft practiced technique, and it is felt to give everyone in the pack riding wash a faster overall time (although the lead canoe will change hands several times over the course of a long race). I've never seen it stated or implied that having another marathon canoe ride your side wash will slow you down, and even if a canoe is riding your stern wash, I think the only effect is psychological drag. So, can any hydrodynamic expert out there explain why having another dragonboat ride their side wash would slow the lead dragonboat down????

Energy dissipation. The presence of another object that prevents the dissipation of energy outward causes the energy to be reflected back. Same concept as depth and the energy dissipation downwards. You probably don't feel it in marathon boats because their proximity and relative size is not the same as in dragonboat.

"Energy dissipation. The presence of another object that prevents the dissipation of energy outward causes the energy to be reflected back."


Right.. but the dragon boats would need to be very close to each other (like a foot) for this to have a slowing affect on the lead boat. People claiming that wash riding slows the lead boat are just looking for a reason to wine.. it doesnt happen. Note the picture of the huge boat and how close another boat would need to be to be affected by energy dissipation

so by your logic we only need a foot of water deeper than the bottom of the boat then? Same concept as depth

Instead of guessing, why not test it.

Use the montreal festival (known for it's excellent drag) and see if boats in early heats where they have no trailers go faster than in the final when people are riding them.

I don't see why you would need to be within one foot of another boat for energy dissipation to take effect. I aggree that it's exactly the same effect as water depth. Having another crew beside you is going to change the local pressure on your boat, because the energy in your wake doesn't have the same room to dissipate.
Another point I'd like to make is that its not that your boat slows down, its that your boat becomes heavier. This will mean that you have to work harder to maintain the same speed. Small difference, but worth noting.
One thing to note is that dr. canoe mentioned marathon paddlers switch the lead boat during a race. If there were no impact on the lead boat as a result of wash riding, why would anyone switch? The riding boats naturally want to stay as riders, and if the lead boat isn't being impacted who cares? Obviously its easier for the riders, so the lead would want to be a rider to take some load off. But its also harder for the lead, so he won't be able to maintain the same speed. As a result, if the same lead stayed in the lead, he would get slower, and the wash ride that all the riders get would get worse as he got slower. That's why the riders voluntarily switch with him, it will make the whole pack faster to constantly have a fresh lead pulling riders, rather than ride a single lead to death.
You can feel the boat get heavier when someone is on your wash. No experiment necessary.

<<You can feel the boat get heavier when someone is on your wash. >>

So your boat somehow weighs more than it did when it left the dock just because someone is riding your wash? The boat does not get heavier; it's the drag that is increased.

that is a pretty picture.

If the Island times are any indication, then having teams jumping on their wash (while helping the times of the teams besides them) did not slow Mayfair down at all. In the Community Championship Mayfair did a 1:55:82 and in the A Final they did a 1:55:85... the teams in the lanes besides them, however, did improve significantly. Now I know what naysayers will argue: there was a number of hours between both races. However, other teams' times did not change significantly either on Sunday between their morning and afternoon heats (see the Blades, Big Fish, U of T New Dragons, etc). Nobody can argue that there's a definite advantage to the teams riding wash, but I wonder how much it really affects the boat in front.

I think this calls for MYTHBUSTERS!

Anyone who has had a crew jump on wash can tell you the impact is imediate, and noticeable. You can actually feel the hit sometimes when another crew grabs the wash. The boat you are paddling feels heavier, but as noted above it is because the drag has increased. It is not dissimilar to paddling in shallow water versus deep water. The boat runs more freely, and feels lighter.

Absolutely more effort is required to achieve the same goal when another boat is on the wash. Everyting else being equal, a crew without a wash rider will run faster times.

To the poster above questioning why marathoners would switch leaders...that is because it is easier when on the wash, so you rest up a bit and then push the pace when leading. They can achieve overall faster times.

I don't think wash riding would have as much effect on the lead boat as some say.

I do agree that the theory is the same as shallow vs. deep water.

The shear wave that propagates from the boat is like a half cone, starting at the bow and propapagating in 3 dimensions through the water below. The angle of the shear wave front (or cone) is about the same through 180d as what you'd see on the surface wake.

But remember the bottom of the course is a continuous plane. When your boat's shear wave hits bottom and reflects back, it does so off a continuous plane.

When you've got a boat next to you riding wash, the energy is only reflected off the (relative to the bottom, say) small side cross sectional area of their boat. The rest of the energy is free to dissipate underneath. The opposing boat is not a continuous plane like the bottom is, it will not reflect as much energy back to your boat.

The effect would be analagous to the ratio of cross sectional areas of opposing boat vs. bottom, i.e. small.

Sure there are advantages to riding wash for the trailer, but the lead shouldn't feel that much, perhaps it's psychological in that the lead has someone right on them.

"perhaps it's psychological in that the lead has someone right on them"

As a paddler I feel a rider hop on before I actually notice they are there. So its not psychological.

At the risk of being nominated for President or being called gay -- not that there's anything wrong with either.

If you agree that a trailing boat to the left or right of the lead boat speeds up (or stays at the same speed but the paddlers can use less power to maintain that speed) by riding wash, then according to basic laws of physics the energy that goes into INCREASING the speed of the second boat must have an equal and opposite energy LOSS somewhere else.

The way I see it, if X is the direction of the boat, and Y is perpendicular to the boat direction, and the primary bow wave is propogating in some component of X-Y, then the trailing boat can be said to be blocking the wave from moving in the Y direction (and reflecting it back towards the leave boat) while getting a boost from the component of the wave propogating in the X direction.

So the energy that helps the trailing boat go faster is supplied by the lead boat. Kinetic energy from boat speed into potential energy of the bow wave into kinetic energy of boat 2.
Either the lead boat is slowed, or more power from the paddlers is required to keep the lead boat at a constant speed.

QED

Game. Set. Match.

From the Padawan himself.

The energy that propels the wash rider is in the wave. Therefore it is the wave that loses energy, not the boat generating the wave. However, the boat will require more energy to move forward at the same speed if energy is reflected back on it.

Interesting read Joel...

JOEL FOR PRESIDENT!

Intersting points, although I think the wash riding boat is not just a small plane as you suggested, but it, too, is sending off a 1/2 cone of energy wave. So the lead boat is not only contending with the bottom of the river/lake and the side of the riding boat, but also the wave it is also sending (which resembles the 1/2 cone).

Yes, shallow water is a big impact - probably bigger than wash rider(s), but noentheless, was riding boats have a significant impact (and more significant as this boat gets closer to the lead boat)

Joel's answer sounds good, but the riding boat is not absorbing energy from the lead but but gettig the energy from the wash, therefore it is absorbing energy that would otherwise just propagate out through the water in the form of the wave.

My theory on this is that, if the riding boat is close enough to the lead boat (Laterally) that there own wash can interact with the back of the lead boat, it will therefore disrupt the course of the lead boat. If however the riding boat is far enough away from the leading boat that there wash propagates behind the lead boat the should be no effect. This could explain why there was little effect at the Island, since if a lead boat is in the middle of their lane and there are ghost lanes like on the island, there should be at least a 6 meter separation between the boats, even if the riding boat is hugging it's bouys

this has always been one of my fave topics on this forum. My experience: yes, there is a slowing effect for the lead boat, and a 'drafting' effect for the following boats. Of course, you don't get the effect of drafting (as in car or bike racing) on the lead boat (where even the lead boat gets a reduction in drag) unles you were to be right behind the lead boat (effectively 'lengthening the keel' of both boats).

I think I posted this article or somethin related to it years ago. Good little experiment.

Auteur(s) / Author(s)
GRAY G. L. (1) ; MATHESON G. O. ; MCKENZIE D. C. (1) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) Univ. British Columbia, Allan McGavin medicine cent. school human kinetics, Vancouver, CANADA
Résumé / Abstract
A common technique employed in flatwater canoe races is «wash riding», in which a paddler positions his/her boat on the wake of a leading boat and, at a strategic moment, drops off the wake to sprint ahead. It was hypothesized that this manoeuver was energy efficient, analogous to drafting in cycling. To study this hypothesis, minute ventilation (VE), heart rate (HR) and oxygen consumption (VO2) were measured in 10 elite male kayak paddlers (age = 25 ± 6.5 yrs, height = 183.6 ± 4.4 cm, mass = 83.9 ± 6.1 kg) during steady-state exercise at a standardized velocity in conditions of «wash riding» (WR) and «nonwash riding» (NWR). The data were collected in field conditions using a portable telemetric metabolic system (Cosmed K2). Statistical analysis of the mean values for VE, VO2 and HR was performed using the Hotelling's T2 statistic and revealed significant (p < 0.05) differences between the WR and NWR trials for all three dependent variables. Mean values for VE (l/min) were WR = 113 ± 16.5, NWR = 126.3 ± 15.7; for VO2 (l/min) were WR = 3.22 ± 0.32, NWR = 3.63 ± 0.3; and for HR (bpm) were WR = 167 ± 9.9, NWR = 174 ± 8.0. It was concluded that wash riding during kayak paddling confers substantial metabolic savings at the speeds tested. This has implications for the design of training programs and competitive strategies for flatwater distance kayak racing
Revue / Journal Title
International journal of sports medicine ISSN 0172-4622 CODEN IJSMDA
Source / Source
1995, vol. 16, no4, pp. 250-254 (20 ref.)

Here was another related one

Titre du document / Document title
Importance of wash riding in kayaking training and competition
Auteur(s) / Author(s)
PEREZ-LANDALUCE J. ; RODRIGUEZ-ALONSO M. ; FERNANDEZ-GARCIA B. ; BUSTILLO-FERNANDEZ E. ; TERRADOS N. ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
Fundación Deportiva Municipal de Avilés, ESPAGNE
Department of Functional Biology (Physiology), University of Oviedo, ESPAGNE
Unidad de investigación, Hospital Central de Asturias, ESPAGNE
Résumé / Abstract
Purpose: The use of different wash-riding techniques is common during kayak training and competition. Changes in wash-riding positions could imply a different exercise intensity. The aim of this study, therefore, was to quantify the energy savings made when a kayaker is wash riding. Methods: Eight male international flat water kayakers, who performed a field test of 2000 m in each of the four wash-riding positions, head (H), right wave (RW), left wave (LW), and end position (V), were studied. The data investigated were: time, stroke rate, blood lactate (BL), heart rate (HR), and rate of perceived exertion (RPE). Under laboratory conditions kayakers performed the same intensity of exercise in a kayak ergometer, and HR, oxygen uptake (VO2), BL, mean power output (W), and RPE were measured. Results: The results show significant differences (P < 0.05) among H, RW/LW, and V. The mean values for BL (P < 0.05) were 4.2, 2.0, 2.2, and 1.5 mmol.L-1, for H, RW, LW, and V, respectively. RPE also revealed differences, with values of 15, 12.6, 12.6, and 9.7 for H, RW, LW, and V, respectively. Mean power output gave values of 190.3 (H), 155.6 (RW and LW). and 129.5 (V) W. HR was different between H and V (172 and 151 while stroke rate was different among the parameters H, RW, and V (93.7, 88.8, and 87.6, respectively).The VO2 in the kayak ergometer test showed a difference between H and V (3.78 and 2.23 L.min-1 ). Conclusions: We conclude that wash riding involves a saving in energy cost of between 18% and 31.9%, depending on the position. This conclusion is of importance for the quantification and calibration of kayak training and competition.
Revue / Journal Title
Medicine and science in sports and exercise ISSN 0195-9131 CODEN MSPEDA
Source / Source
1998, vol. 30, no12, pp. 1721-1724 (17 ref.)

Hey Paku that's a good point I didn't mention the cone coming off the wash rider's boat, because didn't think it mattered.

Say for example's sake both boats produce a wake / cone angle such that it's 2m out from each side at the very back of the boat. In order for the rider's boat cone to interfere with the lead boat, the boats would have to be neck and neck, 2m apart. As soon as the riding boat moves back at all (or away, even a little bit) then they don't interfere.

Okay so what about energy reflection, as stated earlier?

Let's assume that as in my last reply, the riding boat does have some cross sectional area that can reflect energy. Then let's assume that in my second reply here, the rider's boat's cone cannot possibly reach the lead boat (because lead is too far away or in front).

The only way the rider can affect lead is if the energy reflection is somehow transmitted past the shear cone front. So here's an experiment to see if energy can be reflected through the shear cone, forward to the lead boat.

Find a dock that sits about as low in the water as a dragonboat. Do a full race piece, lining up a few hundred metres away. GPS speed before, and next to the dock (offeset about as far away as a wash rider would be).

The dock acts as a small cross sectional area reflecting surface that doesn't produce a shear cone (i.e., as the riding boat would, but lead boat is ahead of it's cone, so the dock is only replicating the rider's ability to reflect energy forward if possible).

There's no doubt the dock will ripple (harnesses the energy you put in as you went by, like a rider would) but will it really slow you down?*

*hopefully the start and finish of the piece has same water depth in anyone's experiment because this should have a greater effect than the dock!

This thread is interesting because the evidence seems to be there although we have all these differing ideas about why / not why.

This image shows the pressure contours on a simplified boat traveling at 15 km/hr

?t=1214597333

While this image shows the same contours on two boats traveling 1.5m apart with a 1m stagger

?t=1214597446

You can see a clear change in the pressure distribution for both boats. Both boats would see a change in their drag as a result. This model doesn't show the effect of the wave that the rider is riding, as it is a very simplified model. But I would say that the extra force gained from riding the wave more then makes up for the increase in drag that the rider sees, while the lead boat sees an increase in drag with no gain from wave riding. Take this with a grain of salt as it is very simplified, but there is clearly an impact on the lead boat.

Good job Doyle, I love how you always back up your opinions with real scientific proof. Now let me take your OC-1 out for a spin man.

Interesting thread...I'm not normally a poster but couldn't resist getting dragged into this one (ouch, bad pun). I'll start by stating that I'm a layman so can't attribute what I write to anything but common sense and synthesis of information already stated in this thread.

Observation: It appears that there's a natural split on this thread between tracing cause and tracing effect. Most agree that wash-riding positively affects the trailing boat. Less agree that wash-riding negatively affects the leading boat. Even less have offered an explanation as to the cause of either effect (assuming they exist).

Opinion: My experience indicates that there is an effect on both boats.

Hypothesis on cause: On the assumption that fluid dynamics apply consistently to aerodynamics and hydrodynamics, the concept of aerodynamic drafting would apply to both boats in motion. If a tight line of cars or bicycles can create an air "cocoon" that envelopes the moving bodies creating efficiency for the collective; it would stand to reason that the further apart these bodies drift, the more stress is placed on the integrity of the "cocoon" until it breaks down and starts to create inefficiency for all in the form of turbulence. When a trailing boat rides wash, it's handicapped by the turbulence as much as the leading boat(hold that disbelieving thought for the last paragraph). The inefficiency applies until the bodies drift far enough apart that they are outside one another's sphere of dynamic influence (i.e the feeling of breaking free when you get open water).

The concept would apply in all three dimensions (the cone analogy above) so - from the vertical perspective - a uniform water depth throughout the race course would be perceived as having no affect on a boat because the drag is constant. Shifting to the horizontal perspective - If you apply this theory discretely to all the lanes in the race course, it supports the "lane bias" argument. If all boats are moving forward in different water depths, the dragging force of the bottom is greater on the boats that are closer (i.e. in shallower lanes).

Here's a good time to reiterate that this is a hypothesis on my part....Because water is more viscous than air, I believe there is a natural release point at the water surface. The wake created by a boat's friction driving through the water is dissipated in the form of diminishing concentric waves. The ability of a wiley cox in a trailing boat to jump onto those waves results in the sudden relative ease that a crew feels when they are wash-riding. Jumping onto a wave is hard work because a crew needs to fight through turbulent water to get close enough to a leading boat to benefit from the propulsion, but once their on, it feels much easier. This is the same idea as a surfer jumping onto a wave and riding it. Once in a wash riding scenario, the turbulence is equal on both boats, but the trailer gets the advantage of riding the leader's wave. The leader gets nothing but turbulence from the trailer.

My $0.02.

wash riding doesn't work like drafting, its best if you don't use it as an analogy. You're actually off to the side and still breaking your own water, whereas drafting in cycling is behind a leader, using him to break the air. Cycling and paddling are very different because they are two phase systems. Cyclists only move through air, whereas paddlers move through a gas-liquid interface (air on top of water). Using your analogy, when you're wash riding, you are in fact outside of the cocoon, on its leading edge.

Riding wash is much more like surfing in terms of how the advantage is gained. The energy (pressure) dissipating out from the lead boat creates a wave, which you ride to your advantage. The presence of a second boat will change the upstream pressure distribution for both boats, which will alter the drag felt by both boats. Hence the increase in drag for the lead boat.

Turbulence does not slow boats down on the whole. Turbulence is a measure of the 'randomness' of a fluid. Both boats will have comparable turbulence intensities, around 2%. Drag is much more important.

Good feedback Doyle...thanks

Perhaps I used the wrong word with turbulence. I'll elaborate the idea as interference to the natural dissipation of energy. If the natural dissipation flow of energy is impeded, I assume it will follow the path of least resistence. With another boat next to the leader impeding the natural dissipation path, the energy would deflect upward (and back down due to gravity), backward (where a good portion would be deflected by the lead boat itself), and downward (where it would inevitably deflect off the bottom). Every deflection of the energy wave creates impedence to its release that is inevitably felt as resistence on the blade of each paddler in the lead boat. Those in the trailing boat are subject to the same forces, but get a break in two ways. The first is the surfing effect that speeds up their boat. The second is the fact that by virtue of being ahead of them, the lead boat is impeding less of their disspation path.

It may be simplistic but I think it's logical. If there are any influencing factors that might revise the logic, I'd be interested to understand them.

Exhibit A: Affect of boat was on craft,




CASE CLOSED.

Popcorn kids! Yum!

Here are a couple of papers on the subject.

Importance of wash riding in kayaking training and competition
http://www.acsm-msse.org/pt/re/msse/abstract.00005768-199812000-00010.htm;jsessionid=LmLLhk1vg3pJMj0zQQzC4qLSG9Wk7pLnQnQf6wGT4yLJsm34TMJ2!-1848465507!181195629!8091!-1

The metabolic cost of two kayaking techniques
http://www.ncbi.nlm.nih.gov/pubmed/7657419

Another way of looking at this subject by looking at the physical impact of this technique.

The effect you notice on the lead boat is probably a result of influences that a boat riding side wash has on the steering of the lead boat rather than drag. A boat that is riding wash too far forward will cause the boats to seperate , get pushed apart. This results in the lead boat needing a sigificant steering effort to stay straight. The steering effort causes drag.
A boat riding wash too far back results in the lead boats stern and the riding boats bow being sucked together , again requiring a significant steering effort to overcome and avoid a colision.
There is sweet spot to ride where both boats track straight with little effort. There is little or no effect on the lead boat. The sweet spot is further back farther away from the lead boat and at higher speeds.

The last post makes the most sense to me. All the other theories were either too vague or complicated enough that my brain hurt - but the last post is exactly what I know happens in marathon boats - there is a sweet spot, just the right distance back, and the right distance beside, where you don't get sucked in or pushed away, and it does not slow the lead boat down.

"I think this calls for MYTHBUSTERS!"

Yup! Or the local equivalent, for sure.
Look at all the theory we've had stated thus far, "proving" and "disproving".
GET OUT THERE AND TEST THE DAMN THING!

And what happens when 2 crews are riding either side of a lead boat?

Joel for president of the GAYS!!!

Nice to read a thread with some thoughtful posts.
June 27 with the colourful picture of pressure around the boats :
a question , is the area of high presure twice as large for 2 boats as one ? i.e. is the resistance decreased by boats "sharing the workload "
A note on shallow water : The increased drag in shallow water is a result of the bow wave "dragging" on the bottom , slowing down and getting higher , not interaction directly between the canoe and the bottom. At racing speads we are coninuously trying to push though the bow wave so as the bow wave slows down from friction with the bottom and builds up the boat slows down. In a marathon boat you can actually sprint as you hit the shallows and get ahead of your own bow wave , called popping the boat. If you can get your boat popped you can go very fast across the shallows with reasonable effort , faster than in deep water , even though you have not changed any interaction between the boat and the bottom. If you are not popped you are MUCH slower than deep water as you push against your massive bow wave.