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

Chris Crawford wrote:

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.

This is a fairy tale. If you are cycling, that bubble of low pressure is
_small_. The advantage if you are further back is due to being in turbulent air
and not exposed. If you are talking about getting close enough to a rider to
meaningfully affect the leader's performance, you'd have to be a few centimeters
away. That isn't going to happen. If your butt looks like the rear end of a
NASCAR car and hangs well off the back end of your bike, maybe things will be
different... if you cycle in a hurricane.

In a racing car, they can get quite close - considering the speed at which they
are traveling. If they were racing at cycling speeds, there would be a
negligible effect on the leader's pressure distribution. At their speeds and
given the shape of the vehicles and how close they can get to each other (where
the size of the vehicle is still significant) they can get into the other's air
flow where it is still influencing the lead vehicle.

This is cross-posted to rec.skiing.nordic - a newsgroup I gave up on years ago
due to the amount of BS that's posted that passes for science, physics and
mechanics. I guess things haven't changed.

Mike

I'm sorry if I gave the impression that any gains by the leader are
"meaningful". I don't beleive that they are any more ceraminc bearings
or hollow-pin chains will improve your cycling performance. It's just
a theoretical fun and games.

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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