Another look at drafting- does it help both the leader and the follower?

[blueplanetsurf]

I just watched this video posted on the Quickblade facebook page.  I never thought of this but in car racing two cars drafting can go faster than one car alone, it helps both cars.  The lead car benefits as there is less drag from turbulence behind the car.  I wonder if this applies to SUP racing as well.

[PonoBill]

Almost certainly. You can approximate a longer waterline.

[XLR8]

That would be real interesting to look at for sure.  Here in the Great Lakes drafting hasn't really shown up significantly in our races.  But there are almost twice as many races this year, including some that are attached to OC and surfski events.  It'll be interesting to see the perspective potentially change.

Right now I would define the general attitude to be "Pull your own race." I have heard racers make  negative comments to other racers who use the draft technique.  I tend toward the pull your own race attitude, but recognize drafting as a legitimate skill to be practiced and learned.

This may all sound like tangent to the OP, but it isn't meant to be.  My general point is that at the young age of SUP racing here in the Midwest I believe drafters to be looked at as parasites.  Blue Planet's post suggests a symbiotic relationship.

[Tom]

Can someone explain what drafting does. I know drafting works in bicycling by cutting the wind, but is only effective at higher speeds, not the 5 or 6 mph a board is going. Does SUP drafting have a similar effect on the water?

[PonoBill]

Probably, if the paddlers are close enough together. The hull speed of a displacement craft is a function of the waterline length. The hull creates a wave with a length equal to its waterline. To exceed hull speed and plane the hull has to climb up over the bow wave. That takes more power than humans can generate.

The speed of a wave through water is a function of it's wavelength, the longer, the faster.

The wave generated by two hulls in close proximity would probably not be exactly the sum of the hulls, but the interference between the stern wave of the leading boat and the bow wave of the following boat would certainly have some effect.

One more thing to test, though it seems like something that would have been done a hundred years ago. I do know that the reason tugs prefer to push a barge instead of tow it is that it makes for a faster trip.  

Looking at the picture above it looks like the train of four drafters has a completely different bow and stern wave than the guy in the clear in blue trunks. The waves are muddled, but the effective length looks long.

[headmount]

Splish splash, I'll be right behind you today.

[catdailey]

I'm guessing that it doesn't help the paddler in front. I vaguely remember from my cycling racing days learning that the lead cyclist did not benefit from a drafting cyclist, but that the drafting cyclist enjoyed a 20%? Reduction in effort required to sustain the same speed (might have been as high as 30%?). My guess is that the speeds set by human locomotion aren't high enough to create enough dirty air behind the moving object to make having that turbulence filled in advantageous, unlike a race car.  And I might be talking completely out of my behind, too

[blueplanetsurf]

If you look behind you when paddling fast, you will see there is a lot of turbulence, which I'm sure creates quite a bit of drag, so it makes sense that someone following right behind would reduce the turbulence of water coming back together behind the board.  Like Bill said, it effectively lengthens the waterline.  I have no doubt that drafting behind someone takes less energy, the question is if it also helps the board in front.

[PaddleCrazy]

Just a couple related thoughts from a couple other sports that I used to participate in....

Used to bike a lot with several guys, and "drafting" was a definite plus for the group; as we were able to average several mph's more working as a group, as opposed to the individual who is separated from it.

Most of that was simply to break the wind resistance, as the lead rider would get hammered, and we were changing riders all the time when trying to keep our speed up as high as possible.  I'm sure that SUPing is not effected as much with wind resistance, as the speeds are no where near the same, but I would think that there is at least a little advantage to be had in the group, than as the individual not in it and trying to catch them.

Second, used to water ski a LOT, and while we all dream and talked about getting out early on the "glassy" lake.....when we did get out in those conditions, we were actually disappointed with the actual performance of our skis in those water conditions.

When it was "glassy", our skis would "stick" to the water and slow us down in everything we tried to do, regardless of the boat's speed.  With a little bit of ripple or chop, the skis would free themselves up, and we'd be able to really accelerate hard out of the turns, rather than feel as though the ski was getting "grabbed" by the water.

I would expect the same thing, if not more, with the increased surface area of an SUP.  So while the lead SUPer might not be going any faster, he's breaking up the "surface tension" of the water for those behind him, and as a result, they're not working as hard to keep pace with him......assuming all SUPers in the group are at approximately the same level (I'm sure that if I'm following Danny Ching or someone like that, I ain't keeping up for very long at all    ).

Just some rambling thoughts.......

[blueplanetsurf]

I wrote a about my drafting experience and theory in this post about the Hennesey's and Tahoe races:
http://zenwaterman.blogspot.com/search?q=hennessey

The stock race:
I got a decent start and soon found myself drafting behind TJ Saeman with Shakira Westdorp and Brandi Baksic following close behind. We were following TJ like ducks in a row. I tried to pass TJ a couple of times but he would pick up the pace and I could not pass him so I kept falling back into the drafting position. This was the first time I drafted in a race and I was surprised by how much much less energy it took to draft than to cut through the chop. I think the water coming back together behind the leading board creates a small bump that you can actually ride, also the water gets smoothed out and pulled forward by the lead board. This drafting effect seems to be even more pronounced in the third or fourth position. The tricky part is to maintain a close distance to the board in front of you without bumping into the tail and without going off course. I focused on the tail in front of me and usually switched my paddle one or two strokes after the lead paddler. I had to constantly adjust the power of my stokes to maintain the right speed. I would estimate that I used 15 to 20% less energy when drafting on the 12'6" stock board, which is significant. On longer unlimited boards with their smooth water entry and exit, drafting is probably less effective.

I also used drafting in the Tahoe race the following weekend (see post)

[starman]

I spoke to Chuck Patterson after the SoCal 2011 BOP distance race. He was lamenting about all the drafting going on. Turns out being the one in front of one pack for a time he had to do a lot of work for the train. Unlike the road bike dudes and flying ducks there was no sharing of the lead position. Pretty much drained his tank by the 3/4 mark.

[Waves4supper]

I think there's no advantage for the leader, and a two-fold advantage for the follower:

- he has less wind resistance if the wind is head on

- because of friction, a hull moving through the water will take along a lot of "entrained water" (boundary layer in naval achitect's terms). I am sure there must still be a forward component in the water when the following paddler comes (even if it looks turbulent). So at least to some extent (but it could be negligible), he's paddling downstream in a river.

To check this theory, it would be good to hear from racers if they still use drafting when they have apparent wind from astern, or (even better), are paddling along with the wind at windspeed (resulting in no aerodynamic resistamce).


Theoretically, there could also be an advantage for the forward paddler, namely if the hull of the following paddler "fills the hole" of the depression just after the stern of the first board. It's the waterlines being forced back up after your board has passed which slow you down (to some extent). Keep the flowlines horizontal (as with the cars in the youtube video) and you will have less drag.
But given the sharp entry of most raceboards, I doubt very much this would give any positive effect. Another aspect is that there is very little immersed stern area on the leader board, when comparing with how a racecar is shaped.

Bruno

[catdailey]

Blueplanetsurf:

That's the whole question.... In car racing and cycling, the advantage to the car/bike drafting are the reduction in wind resistance; the surface they are on doesn't change. In cars, it appears that the lead car also gains an advantage because the drafting car fills in the turbulent air behind the lead car. The surface (road) doesn't change like water. With cyclists, to the best of my recollection, the lead bike in a draft train does not attain this advantage like race cars, and my guess is that the speeds are too low to create this benefit (dirty air behind a cyclist is a whole magnitude smaller than that behind a race car). In small boat races, the drafting vessel (to the best of my understanding) gets a two fold advantage:

1. Reduction in wind resistance (maybe? if a windless day....don't know if drafting board and rider are effectively too far behind lead board to get that reduction in dirty air....cyclists, cars have to be very close together...riders on long boards are pretty spaced apart so the dirty air might still remain behind the lead board before it encounters the second rider's body) ; most definitely if in a headwind; not sure about sidewinds and yaw.
2. The ability to ride in the lead board's wake which has more to do with fluid dynamics than wind turbulence. I think this has been pretty well established in small boat research.

The question then becomes: does the front board also gain an advantage by virtue of the drafting rider either filling in the wake (turbulent water, not air) or by effectively lengthening the waterline of the lead board (might be one and the same question).  Conversely (and I don't know anything about this one), shapers always talk about a board's release. Might a drafting board, instead of aiding the lead board, slow the lead board by interfering with the board' release at the tail???

It should be easy enough to measure n a windless, flat day...

[JC50]

We've drafted with 21' OC1's and it made significant difference. This isn't like cycling unless you have a strong breeze against you that the guy in rear can hide behind, but considering the distance between paddlers (>10'), the wind-drafting effect is marginal. With bicycles, you have to be right on the rider in front, so that's only a bout 2-3' separation between bodies, and you can feel yourself getting inside the bubble. Often with riding you have to be a few inches on one side or the other since rarely does the wind come from straight ahead.

So back to drafting boats...yes it works. I can't tell you exactly why, only that I've experienced it and it does work, but I don't think as dramatic as cycling/auto racing (highest paid engineers in F1 are not engine mechanics, they are aerodynamicists). So I see no reason why not in SUP.

So theoretically, if you have a group of paddlers that share the front you all should be faster than the soloist, considering all other things equal (fitness, board, etc...). Drafting behind a strongman (ie: CP, etc...) and not taking a turn at the front is selfish. A good poke with your paddle to toss him off his board should cure him of that and rid you of a parasite. Really now, why be nice to somebody like that.... Taking turns at the front also takes practice, the front man should paddle a bit to the side and immediately accelerate as the train goes by so not to lose his place in the rear. If you have a group of pals who regularly race together and are similar in speed, the group draft "peloton" would be a great thing to practice and become good at. I would guess that you would all be a little faster together than apart. For more info, google "cycling peloton" to read how cyclists do it.

The real drama starts when getting towards the finish line...who's gonna break first? Since paddling is slower than riding and a "jump" isn't as fast a burst as in other sports, this would interesting.

Sounds fun.

[catdailey]

I know that drafting works....been a racing cyclist for many, many years as well as a small boat racer. The question this thread raised was does the LEAD board gain an advantage, too?  And we are not talking about advantage gained by taking turns at the front, but at any given point in time, does the LEAD board gain an advantage by having a drafting board.  Anyone have any real research on the subject?