Science behind speed and glide

2 months 2 weeks ago - 2 months 2 weeks ago #34412 by Watto
Throw a  basket ball into the wind and then a javelin SpaceSputnik... hmm. One reason skinnier boats faster is reduced 'frontal resistance' (drag in this case). Also quoting the ubernet the length of the water line does effect the speed of some boats. ... The longer the boat, the faster it can "theoretically" go because it takes longer for the bow and stern wave to become one wave.

Fat and heavy V7 a reluctant glider. :)

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2 months 2 weeks ago #34413 by SpaceSputnik
Certainly is.

Current: Think Evo II
Past: Epic V7

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2 months 2 weeks ago #34414 by uk gearmuncher
If you want to see the impact of boat run (and to finally answer the others posters confusion as to how his boat seems to be breaking the laws of physics) use an aftermarket smartphone app like 'Rowing in Motion'. Yes, its designed for rowing really but if you mount it on your boat, it will pick up the acceleration patterns and you'll see what's actually going on. I've used it to test various paddlesport equipment.

Previous Boat Journey: Gaisford spec ski, then Fenn Bluefin, then Epic V8 Pro, Now a Epic V10 Sport and a Nelo 550L coming in soon.
Recent Demo's: Epic V10 G3, Nelo 550L, Epic K1t
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2 months 2 weeks ago - 2 months 2 weeks ago #34422 by RedBack
If I may just add my humble input...

I think there are two aspects being conflated here.
1. Boat run
2. GPS latency


Boat Run:
It's been well known for a long time that a ski or kayak travels fastest during the brief moment after the paddle releases from the water, so long as (a) the blade is accelerated through the duration of the stroke and (b) the release is clean and to the side (not lifting water).  In other words, the speed of the boat between strokes is largely dictated by the speed at which the paddle leaves the water.  The duration of the "accelerated glide phenomenon" is rarely more than .25 seconds and by .5 seconds the boat has slowed to the point where a further stroke should be initiated to maintain a reasonably constant velocity.  The higher that velocity, the more quickly the craft will slow due to the non-linear relationship between speed and drag.

GPS latency:
Most of us use small GPS devices such as Garmins or equivalent.  These are great for measuring relatively constant speed and providing us with data for later analysis.  They are not accurate for periods of rapid acceleration or deceleration.  While they have improved in recent years, their latency is still typically in the region of 1 - 2 seconds, - driven by the time required for positional data acquisition and subsequent processing within the unit.
Consequently, if you accelerate your boat during the stroke, that acceleration will only register on the GPS after your blade has left the water.  The longer you pause (up to the latency period of the GPS) the more pronounced this "Glide acceleration" will appear to be.  The acceleration is real, - it just happened 1-2 seconds ago...
If we were all using RaceLogic or Leica GPS units, then the latency would be down in the 100ms range, but since we're not, we're stuck with the delays.

Don't stop using "pause paddling" as a training drill though (or even "micro-pause" paddling during a distance race).  It allows you time to "set" your body position to optimise the power and efficiency of each stroke and let the boat work for you.
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2 months 2 weeks ago #34436 by mcnye1
Well, the Laws of Motion are pretty much settled science thanks to Sir Isaac.  In order for your boat to accelerate, there has to be a force pushing it.  With your paddle in the water, the forward force generated by the paddle exceeds the drag (backwards) force and the boat accelerates forward.  Sometime during the exit, the net forward force goes to zero and the boat stops accelerating.  With the paddle out of the water, the only force acting on the boat is the rearward drag force so the boat starts decelerating.  

Without a doubt, the phenomenon that you are seeing is a byproduct of how your GPS unit computes speed.  Below is a discussion of GPS speed that I have previously posted on this board.

 A bit of a warninghere. GPS is a subject where I have significant technical knowledge as a result
of work. IMHO, the number one error of consumer level GPS users is to over
estimate the speed accuracy of GPS. Caution: Geeky Math Follows! GPS calculates
speed by determining the distance travelled between fixes and dividing by time.
At surski speeds (~7 mph), you cover approximately 10 feet per second, so to
get a good 2 sec speed reading, the unit has to be able to measure 20'
distances accurately. The problem is, GPS is not nearly that accurate.
According to the owner of the GPS system (US Government), consumer grade
non-augmented GPS receivers have an accuracy of about +/- 16' (the spec
accuracy is generally 30'). This means that when a GPS tries to give you a two
second speed reading, it will measure the distance as 20' +/- 16', which
results in a speed reading of 7 +/- 5.5 mph. GPS manufacturers recognize this
limitation so almost all add speed smoothing algorithms to their processors so
that you as a user do not see that much error. This is also why GPS units
significantly lag any changes like when you speed/slow while doing intervals.
From a technical standpoint, you need to be at a steady speed for about 30
seconds before the speed displayed on your GPS can be considered statically reliable
(<5% error).  Very high end (Aviation and Professional Marine)GPS units are much better WRT speed for two reasons.  First, they all employ augmentation (WAAShere in NA) which improves the average accuracy down to <1 meter.  Secondly, they operate at a higherfrequency.  Most consumer level GPSreceivers operate at 1 Hz, where high end units operate at 5 or 10 Hz.  The operating frequency of a GPS receiver isreally more like the clock speed of a computer. A 1 Hz GPS calculates position once per second where a 10 Hz unit doesit 10 times per second. 
 
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2 months 2 weeks ago #34437 by zachhandler
Thanks mcnye. That explains the appearance of magical acceleration during the glide phase. And i think patrick’s explanation about getting a cleaner catch and earlier exit explains the fact that many of us do go a bit faster on average when we slow down the cadence. For elites, who have perfect technique no mater how fast they spin, slower might not be better. I remember seeing an interview with johnny puakea (boat designer, former elite paddler, former US sprint kayak team coach) in which he flips the paradigm on its head. He advocates that rather than moving the blade fast through the water and slow through the air, one should do the opposite. He says move the blade slow and gentle through the water, then whip it fast through the air. The rationale is that the harder one pulls the blade through the water, the more water slides off the blade creating turbulance and wasting energy. As soon as the blade is in the air the boat is decelerating and will need a greater force to bring it back up to speed with the next stroke. This makes a lot of sense to me.  Distance cyclists spin a small gear instead of mashing a big one slowly. Distance runners (in comparison to sprinters) do the same. From an engineering perspective, a finely controlled thermostat is more efficient than one that allows large fluctuations in temperature before reacting. I suspect Puakea’s strategy requires good technique as for most of us self taught hacks our stroke becomes ratty at higher cadence. 
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2 months 1 week ago #34438 by mrcharly
I agree with everything mcnye says about GPS (although I'm not a GPS expert). Earlier I advocated testing one paddling technique over several km, vs another technique, taking the time for each test.
However, I do take issue with the statement about 'there are no other forces on the boat once the paddle is out of the water'.
This ignores the lift of the boat. Unless the paddler is going very gently, there is a surge with each stroke, lifting the boat. As soon as the paddle stroke effort reduces, the boat starts to sink again. The lifted boat (and paddler), as a system, contains stored potential energy. The energy has to go somewhere! It might be into creating more wash, rather than motion, or, at some speeds (dependent on hull shape), it will produce a forward surge, as the boat surfs forward on its own wake.
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2 months 1 week ago #34439 by SpaceSputnik
Can someone give a definition of "letting the boat run"? I am still hazy if we are talking about a hydrodynamic phenomenon or its purely a technique optimization during a pause.

Current: Think Evo II
Past: Epic V7

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2 months 1 week ago - 2 months 1 week ago #34440 by Watto
What a lot of bullsh#t, you guys have no idea what you're talking about. There is no doubt whatsoever that I was paddling at my best on the flat no tide, no boat wash in a 100 metre sprint on Friday eve as below from my Garmin Strava data at 18.7kmh in my NK Squall 58:



Unfortunately I was racing a mate in a Stellar SEI G3 side by side the whole way (this point about 30 metres into the 100 after about an ocean paddle) and his Garmin data says:



Hmm my otherwise reliable Garmin 920 XT has me at four kmh faster at the same point as my mate with his Garmin Fenix (speed good but watch heart rate is BS though). And of course I wasn't getting windburn at nearly 19 kmh. All of my previous data has me here at about same speed between 14-15kmh. The real issue was GPS. So yes even independent of lag time and limited effective GPS accuracy by the second, sometimes data is outright incorrect for whatever reason. 

Afternoon/evening paddle this evening Sunday flying upriver at mouth of the Swan (Traffic Bridge) 20 knot breeze at my back (very little fetch so really only ripples) - 9.5kmh!! Return journey into same fresh breeze, minimal resistance waves - 11.6kmh!! WTF?  Significant tidal flow in still a wide part of the river makes a big difference.

Tide and wind variables in addition to GPS reception effectiveness also mess with data accumulation. I'm liking the V Box Sport a lot! Trouble is of course AU$600 plus. No honey, I absolutely need this one..
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2 months 1 week ago #34443 by juki
Replied by juki on topic Science behind speed and glide
Probable timing and technique optimising.......I am more a rower but you try to  get the maximum distance each stroke and do as little as possible to slow the run of the boat. Clean exits and entries and balance and control when you change direction of body position to start next stroke. But there is also a point where boat starts to decelerate faster and you need to start next stoke before then.....for maximum run each effort.....trade offs once racing sprints......not sure explained it properly......I Can explain it whilst rowing but writing it down and also not sure about transference to  surfski......

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2 months 1 week ago #34444 by RedBack
Hmmm...  as a matter of interest, - how many World Champions/Olympic Gold Medalists has Johnny Puakea trained with this "slow through the water and fast through the air" approach?
Also, - how many team-boat medals have been won with this concept?
Just asking...

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2 months 1 week ago #34445 by zachhandler

RedBack wrote: Hmmm...  as a matter of interest, - how many World Champions/Olympic Gold Medalists has Johnny Puakea trained with this "slow through the water and fast through the air" approach?
Also, - how many team-boat medals have been won with this concept?
Just asking...


I would guess zero because he no longer coaches K1. He currently coaches OC, and some of his OC athletes are world champions. 

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2 months 1 week ago #34446 by mrcharly
Johnny Puakea is specifically talking about single-bladed paddling.

If you translate that to double-blade, then I think the equivalent would be 'take the blade out of the water fast, then dig deep and powerful in the stroke'. 

It is well known that 'hummingbird' paddling (high stroke rate dabbing at the water) is inefficient and just results in lots of splashing. Powerful, short strokes are much better.

There is a very good paddler in my club, he grew up doing sprint K1 with a lot of formal training. In a 500m sprint session yesterday he pointed out to me that I was dropping my top hand when I was taking my blade out. Took some concentration to not do this, but what a difference! Stroke shortened, power went up - and the 'in air' part of the stroke lengthened. Make that quick, pause for the set up, pull hard, keep that top hand up as a fulcrum, lift pivot and lift with the lower hand; even this old man was giving the youngsters a hard time.

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2 months 1 week ago #34462 by Watto
Is the test of what you are talking about mrcharly ensuring your recovery hand crosses in front of your face/upper body at a constant horizontal plane? That is some dip below this line at end of stroke - dropping your hand - indicates you are paddling behind yourself? One of my rotation drills is just focusing on top hand travel. 

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2 months 1 week ago #34469 by mrcharly
That's pretty much it, Watto. Not letting that hand dip ensures I take the blade out nice and early - and prevents me from paddling behind myself, as you described. 

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