Hugh P wrote:
[ ]
Watching a marathon kayak race will show you that it is not accurate to
say that paddling fast is just a matter of not making mistakes that
slow the boat down: everyone sprints off the start until the field is
broken into groups (the wash-hanging or drafting effect is immensely
important); then they settle down and paddle less quickly for a while,
except for occasional tactical bursts, and finally there is a sprint
finish. Clearly, the faster parts of the race are not a result of
racers simply being more careful not to slow their boats down, but of
increased effort - much increased, because the boats will be travelling
at somewhere around 'hull speed'.

Hi Hugh : ) It still sounds like perhaps the *average* speed of the
winner *might* well be hull speed or very close to it and the losers
will be less than that, due to mistakes. The bursts above hullspeed
would be tactical and probably wouldn't affect an average much. Yeah,
drafting is a big factor I didn't mention---it's probably effectively
lengthening the waterlines of boats.

There are typical zones for winning speeds for various sports and
probably most sports have more variability than paddling---I bet that
water is a far worse medium than air (for cycling) or snow or, uh,
pavement (for running).

I wouldn't be surprised if hull speed is quite easily attained compared
to the huge efforts required to go even a tiny amount above it. So
sprints would be brief but still serve to sort out groups. The gaps
between paddle groups probably aren't as big as in other sports. The
leaders in most sports are out of sight ahead of me in less than a
minute but in fla****er paddling even when I'm in a slow boat design I
only lose a few yards a minute to the leaders. It gives a very illusory
hope! : )

So I still think the screw-up/skill factor is what makes for the clear
losers rather than the "can't go as fast." Skill involves taking the
best line thru the unknown topography of a water course.

There's also the HUGE issue we haven't even mentioned of SUCK
WATER---in shallow water a boat's natural hull speed is interfered with
by waves off the bottom (maybe?) so hard effort to make the boat go
starts earlier in the speed-range but doesn't spike up as quickly
either, so effort is rewarded (yet overall speeds probably rarely even
hit hull speed in shallow water) and maybe the hull speed limitation
also really relates to the size of the wave---because a lighter team
tends to be able to go faster in shallow water. Is shallow water the
uphills of paddling? I think maybe so! : )

[ ]
To say that hull speed is at about 5lb: that means that to move the
boat at hull speed requires average thrust of 5lb (eg to tow it at that
speed, the tension in the rope would be a steady 5lb). Of course,
paddling is inconstant, so the peak force will be higher.

Maybe the above relates to my coach-pal's remarks. I'll have to ask
him!

I suppose this would relate to skiing such that you'd have to figure
out how much force is needed to keep a skier going his max down a trail
then divide that in half for each arm when doublepoling and if a skier
can't go faster than that speed then that force is the highest they can
sustain. (Like tow the skier behind a snowmobile on a spring scale and
read the resistance.)

Of course, this is mostly guesswork, and this kayak coach presumably
has access to data. I am trying to remember enough schoolboy physics to
calculate double-poling thrust from some flat and uphill time-trials.

He mentioned that "Sea Kayaker" magazine publishes hull speeds for each
boat design they analyze, so I gather that this is a constant which is
determined based on parameters you and I mentioned: shape, length, even
surface finish. --JP outyourbackdoor.com

Hugh

Per jeff potter:
Yeah,
drafting is a big factor I didn't mention---it's probably effectively
lengthening the waterlines of boats.

Does that mean that the draftee gets a boost too?
--
PeteCresswell

(PeteCresswell) wrote:
Per jeff potter:
Yeah,
drafting is a big factor I didn't mention---it's probably effectively
lengthening the waterlines of boats.

Does that mean that the draftee gets a boost too?
--
PeteCresswell

Well, probably not. Don't they even say that bike drafting causes the
leader more work? On second thought I suppose that boat drafting just
means that a following boat can simply find a helpful wave. The lead
boat makes a couple wakes (side and stern). A following boat can climb
one of those waves and put part of his boat on its downhill surface and
go a little faster as a result. I suppose that's all it is. Oh well, it
was an idea... JP

jeff potter wrote:
(PeteCresswell) wrote:
Per jeff potter:
Yeah,
drafting is a big factor I didn't mention---it's probably effectively
lengthening the waterlines of boats.
Does that mean that the draftee gets a boost too?
--
PeteCresswell

Well, probably not. Don't they even say that bike drafting causes the
leader more work? On second thought I suppose that boat drafting just
means that a following boat can simply find a helpful wave. The lead
boat makes a couple wakes (side and stern). A following boat can climb
one of those waves and put part of his boat on its downhill surface and
go a little faster as a result. I suppose that's all it is. Oh well, it
was an idea... JP

Jeff,

I'm not so sure - there is a huge difference in how boats behave on a
sidewave as opposed to a sternwave. My observation is that two (or 3
boats in a chevron) move faster than 1 boat - *provided* that the boats
are of equal power. A slightly slower boat that is able to sit on, but
can't push the lead boat definitely slows the pair down, but two fast
boats that can push each other a bit seem to move faster together even
if they hold position, not trade off. Riding on a stern wave definitely
doesn't seem to 'push' the lead boat, but may slow it down as you are
?maybe? inducing drag on the 2nd wave (assuming you are riding 'in the
hole'). Not so sure I'm explaining this right - it's mostly a feel
thing without the science to back it up.
This is another masters/doctorate thesis opportunity, I think. There
are so many variables that come into play with racing canoes that defy
the normal calculations used to design hulls. Most design calculations
don't even begin to factor suck water, pop water, or the effect of
paddling next to another boat. Much of that has to be derived thru
empirical testing, and is usually done by stripping a boat, seeing if
you like it, and then maybe building a few. Gene Jensen was great at
lofting a boat, paddling it the next week, and then sawing it open and
tweaking it overnight to retest. But very few designers have/had the
kind of instinct or 'butt feel' that Gene had.
With the instrumentation available today - GPS, heart rate monitors,and
strain gauges, it would be possible to actually zero out some of the
variables like paddler effort and develop some objective measurements of
different boat design.

Drafting helps both riders/drivers. Rear rider is helped by decreased
frontal air flow (the obvious one) and the front rider is helped by
having the turbulent air flow moved to the back of the rear rider.
They share the advantage although the gains for the front rider are
much more.

Chris

Chris Crawford wrote:

the front rider is helped by
having the turbulent air flow moved to the back of the rear rider.
They share the advantage although the gains for the front rider are
much more.

Have you got a reference for this? I'm having a hard time imagining two riders
on bikes getting close enough for this to work (yes, I've been a licensed bike
racer).

Mike

In order to benefit from drafting, you've got to be in the drafting
bubble behind the cyclist immediately in front of you. And in a
crosswind the bubble will NOT be directly behind the rider in front but
will be some angle away from them. The effectiveness of this bubble
decreases with the distance, being the greatest if you draft closely
and falling off until there is minimal benefit at 5 or 6 feet. The
important fact is that you will get some benefit 3, or even 4 feet,
back - and it's a lot safer than being directly on the rear wheel of
the rider in front of you.

The rider being drafted also gains a slight advantage. This is
explained by the fact that the low pressure behind the lead rider is
increased in a pace line, giving the leader a slight "nudge" due to the
pressure differential between the high pressure ahead and the low
pressure behind. This is why a NASCAR racing car will go 1-2 mph faster
when being drafted.


From:

http://northwesthandcycleclub.org/Fr...=1152136001681

That was just a quick find on the web but you can find the problem in
any aero/fluid dynamics physics book.

Regards
Chris

On 17 Sep 2006 11:27:02 -0700, "jeff potter"
wrote:

Don't they even say that bike drafting causes the
leader more work?

Some people might say that. I doubt it's true.
--
JT
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