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Date: 03 Sep 2006 08:30:50
From:
Subject: Does anyone test pull?
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Does anyone test pull kayaks to measure drag/acceleration? Might need
to find some really stagnant water or use an indoor pool.
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Date: 09 Sep 2006 02:36:50
From:
Subject: Re: Does anyone test pull?
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Wm Watt wrote:
> galt_57@hotmail.com wrote:
> > Does anyone test pull kayaks to measure drag/acceleration? Might need
> > to find some really stagnant water or use an indoor pool.
>
> I thought of using a spring balance in a river current of know flow
> rate, eg at a river flow station, but was told (by the fellow who wrote
> th KAPER formala, name menmory tenporarily blocked) the he tried it but
> the river current fluxuates too much to get a sufficiently precise
> meansurement to measure very small differences and is not of much use.
>
> However there is one approach that TF Jones has used which works. He
> compared two hulls by putting them both in the same river current tied
> to the ends of a beam which he allowed to pivot in the middle. The hull
> with the most drag pulled it's end of the beam downstream more. It's
> the same balance beam principle used to measure the weight of
> something. In fact if you could compare your boat to a standard hull of
> known drag, just like a bag of grain is compared to standard weights on
> the scale, then you could record the drag. Of course with weights it's
> just some standard at a government Bureau of Standards, and all
> comparisons are relative to that, not to any computed amount.
I had wondered about some sort of balance beam scheme but I could not
convince myself that it would work. After all a bicycle wheel is well
balanced and yet it still turns. If two equal boats were on a beam
wouldn't they still randomly rotate about the pivot point?
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Date: 06 Sep 2006 17:13:34
From: Wm Watt
Subject: Re: Does anyone test pull?
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galt_57@hotmail.com wrote:
> Does anyone test pull kayaks to measure drag/acceleration? Might need
> to find some really stagnant water or use an indoor pool.
I thought of using a spring balance in a river current of know flow
rate, eg at a river flow station, but was told (by the fellow who wrote
th KAPER formala, name menmory tenporarily blocked) the he tried it but
the river current fluxuates too much to get a sufficiently precise
meansurement to measure very small differences and is not of much use.
However there is one approach that TF Jones has used which works. He
compared two hulls by putting them both in the same river current tied
to the ends of a beam which he allowed to pivot in the middle. The hull
with the most drag pulled it's end of the beam downstream more. It's
the same balance beam principle used to measure the weight of
something. In fact if you could compare your boat to a standard hull of
known drag, just like a bag of grain is compared to standard weights on
the scale, then you could record the drag. Of course with weights it's
just some standard at a government Bureau of Standards, and all
comparisons are relative to that, not to any computed amount.
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Date: 04 Sep 2006 05:54:43
From:
Subject: Re: Does anyone test pull?
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Michael Daly wrote:
> galt_57@hotmail.com wrote:
>
> > So the manufacturers have the drag curve but keep it secret?
>
> Whatever data they have, they probably consider proprietary. If you measure the
> kayak dimensions, you can figure out the same info with any number of hull
> design and analysis programs.
>
> Mike
I would imagine that is not so easy to do without considerable time and
effort a huge caliper and maybe a laser level -- and then you have to
trust the software. A pull test should be pretty easy if you can find
some still water or an indoor pool.
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Date: 03 Sep 2006 14:28:07
From:
Subject: Re: Does anyone test pull?
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Michael Daly wrote:
> [...]
> Towing tests are not that hard to do if you're determined. However, since the
> kayak hulls are relatively straightforward, using an established calculation
> like KAPER or Taylor series is close enough and a lot cheaper and easier to do.
> The software for this is available on the web. Sea Kayaker magazine publishes
> this data for all the kayaks they test.
>
> Mike
So the manufacturers have the drag curve but keep it secret?
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Date: 04 Sep 2006 00:17:25
From: Michael Daly
Subject: Re: Does anyone test pull?
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galt_57@hotmail.com wrote:
> So the manufacturers have the drag curve but keep it secret?
Whatever data they have, they probably consider proprietary. If you measure the
kayak dimensions, you can figure out the same info with any number of hull
design and analysis programs.
Mike
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Date: 03 Sep 2006 11:51:49
From:
Subject: Re: Does anyone test pull?
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!Jones wrote:
> galt_57@hotmail.com wrote:
>
> >Does anyone test pull kayaks to measure drag/acceleration? Might need
> >to find some really stagnant water or use an indoor pool.
>
> You'd have to set it up in water moving at a known speed and measure
> the force against a stationary device... to what end would you do
> that?
>
> Boats are tricky because they tend to hydroplane... in atmospheric
> drag, it's a function of the velocity cubed. It is in water, too;
> however, you have *lots* of counfounding issues like weight that
> figure into the mess.
>
> Hobie has that pitot tube "speedometer" that actually works pretty
> well given that the mass is consistent... I suppose I should say
> "*weight* is consistent". If you eat a big lunch, it shows that
> you're going faster. You don't get any measure of force or work;
> however, you can tell a deviation from a base line.
>
> Jones
I was thinking of it as a measure of drag at a specific loading and
speed.
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Date: 03 Sep 2006 21:16:37
From: !Jones
Subject: Re: Does anyone test pull?
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On 3 2006 11:51:49 -0700, in rec.boats.paddle galt_57@hotmail.com
wrote:
>I was thinking of it as a measure of drag at a specific loading and
>speed.
OK, a "fish scale" would work, but how would you repeat the
acceleration vector? I guess you could build a tank and use a pump to
move the water since you aren't going very fast.
Can you change anything based on your data? ,,, given that you get
them, I mean?
Jones
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Date: 03 Sep 2006 18:14:10
From: !Jones
Subject: Re: Does anyone test pull?
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On 3 2006 08:30:50 -0700, in rec.boats.paddle galt_57@hotmail.com
wrote:
>Does anyone test pull kayaks to measure drag/acceleration? Might need
>to find some really stagnant water or use an indoor pool.
You'd have to set it up in water moving at a known speed and measure
the force against a stationary device... to what end would you do
that?
Boats are tricky because they tend to hydroplane... in atmospheric
drag, it's a function of the velocity cubed. It is in water, too;
however, you have *lots* of counfounding issues like weight that
figure into the mess.
Hobie has that pitot tube "speedometer" that actually works pretty
well given that the mass is consistent... I suppose I should say
"*weight* is consistent". If you eat a big lunch, it shows that
you're going faster. You don't get any measure of force or work;
however, you can tell a deviation from a base line.
Jones
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Date: 03 Sep 2006 15:47:47
From: Michael Daly
Subject: Re: Does anyone test pull?
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!Jones wrote:
> You'd have to set it up in water moving at a known speed and measure
> the force against a stationary device
It wouldn't have to be stationary. Towing tanks measure total drag forces from
a moving rig.
> Boats are tricky because they tend to hydroplane...
ICF kayaks don't even start to hydroplane at a speed/length ratio of over 2.2
<http://kayakwiki.org/index.php/Hull_speed >. Not an issue for any sea kayak.
It might be an issue for some of the so-called planing WW kayaks.
> in atmospheric
> drag, it's a function of the velocity cubed.
Drag is a function of velocity squared - power is velocity cubed.
Towing tests are not that hard to do if you're determined. However, since the
kayak hulls are relatively straightforward, using an established calculation
like KAPER or Taylor series is close enough and a lot cheaper and easier to do.
The software for this is available on the web. Sea Kayaker magazine publishes
this data for all the kayaks they test.
Mike
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Date: 09 Sep 2006 17:06:10
From: !Jones
Subject: Re: Does anyone test pull?
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On Sun, 03 2006 15:47:47 -0400, in rec.boats.paddle Michael Daly
<michaeldaly@foo.bar > wrote:
>!Jones wrote:
>
>> You'd have to set it up in water moving at a known speed and measure
>> the force against a stationary device
How would you reproduce the force vector? (Yeah, it can be done;
however, it's easier to hold the object stationary and pump the
water.)
>Drag is a function of velocity squared - power is velocity cubed.
Sorry. Environmental drag (liguid or gas) and the force needed to
overcome it are both cubic. Think about it: you're not moving on a
plane; the boat extends below the surface of the water... if it
scooted along the surface with no penetration, then you'd have a
quadratic function. This is why *any* falling object, no matter how
tiny the coefficient of friction is, will *always* hit terminal
velocity in an atmosphere... the force is quadratic and the drag is
cubic.
>Towing tests are not that hard to do if you're determined. However, since the
>kayak hulls are relatively straightforward, using an established calculation
>like KAPER or Taylor series,,,
Huh??? Why on *earth* would you do that? It's already polynomial;
you use that method when you've got some oddball transendental
function and you want to look at its point behavior. The "series
approximations" give you a polynomial... and we *like* polynomials
because they're easy to manipulate.
You'll usually find series in your calculus II textbook about half way
through the semester. (Teachers like to get *that* part done before
the drop deadline!!!) Please review it before you start spouting
terms to me.
Jones
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Date: 11 Sep 2006 00:42:34
From: Michael Daly
Subject: Re: Does anyone test pull?
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!Jones wrote:
> On Sun, 03 2006 15:47:47 -0400, in rec.boats.paddle Michael Daly
> <michaeldaly@foo.bar> wrote:
>
> Sorry. Environmental drag (liguid or gas) and the force needed to
> overcome it are both cubic.
You don't know anything about drag.
> Huh??? Why on *earth* would you do that? It's already polynomial;
And you don't know anything about Taylor's drag calcs or KAPER.
> Please review it before you start spouting
> terms to me.
You'd better review the whole field of hydrodynamics before spouting your
nonsense.
Mike
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Date: 09 Sep 2006 17:38:27
From: CT CBoater
Subject: Re: Does anyone test pull?
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!Jones wrote:
> On Sun, 03 2006 15:47:47 -0400, in rec.boats.paddle Michael Daly
> <michaeldaly@foo.bar> wrote:
>
>> !Jones wrote:
>>
>>>
>
> Sorry. Environmental drag (liguid or gas) and the force needed to
> overcome it are both cubic. Think about it: you're not moving on a
> plane; the boat extends below the surface of the water... if it
> scooted along the surface with no penetration, then you'd have a
> quadratic function.
The area may or may not be constant, depending on the hull shape, but
given an equal area, the force is proportional to the square of the
velocity. See http://en.wikipedia.org/wiki/Drag_equation
This is why *any* falling object, no matter how
> tiny the coefficient of friction is, will *always* hit terminal
> velocity in an atmosphere... the force is quadratic and the drag is
> cubic....
> Jones
Actually, nothing ever reaches terminal velocity. It only approaches it...
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Date: 09 Sep 2006 22:55:44
From: !Jones
Subject: Re: Does anyone test pull?
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On Sat, 09 2006 17:38:27 GMT, in rec.boats.paddle CT CBoater
<ctcboater@sbcglobal.net > wrote:
>The area may or may not be constant, depending on the hull shape, but
>given an equal area, the force is proportional to the square of the
>velocity. See http://en.wikipedia.org/wiki/Drag_equation
There's some way of calculating it wherein the velocity is factored
giving a drag function that's squared then multiplied by the frontal
area... I have never understood why. Then it's multiplied by the
velocity again.
An engineer explained that it was done that way for the automotive
industry so that high profile vehicles could be compared to others By
the time you're done, though, the velocity has been cubed.
Jones
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Date: 09 Sep 2006 23:05:03
From: CT CBoater
Subject: Re: Does anyone test pull?
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!Jones wrote:
> On Sat, 09 2006 17:38:27 GMT, in rec.boats.paddle CT CBoater
> <ctcboater@sbcglobal.net> wrote:
>
>> The area may or may not be constant, depending on the hull shape, but
>> given an equal area, the force is proportional to the square of the
>> velocity. See http://en.wikipedia.org/wiki/Drag_equation
>
> There's some way of calculating it wherein the velocity is factored
> giving a drag function that's squared then multiplied by the frontal
> area... I have never understood why. Then it's multiplied by the
> velocity again.
>
> An engineer explained that it was done that way for the automotive
> industry so that high profile vehicles could be compared to others By
> the time you're done, though, the velocity has been cubed.
>
> Jones
The power required is proportional to the speed cubed, but the drag is
proportional to the square. At least that's what I remember from when I
took flight propulsion at RPI. And I am a mechanical engineer who
designs cars, FWIW...
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