Is this idea commonly accepted?

http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm

wrote:
Is this idea commonly accepted?

http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm

Well, a 15' downriver racer is faster than a 17' touring boat, maybe.
But this is like saying that a VW Beetle is faster than a Porsche 911
because the wheelbase is shorter.

This site does do a very interesting job of trying to explain some of
the forces that are brought to bear on a kayak.

MJ

wrote in message
ups.com...
Is this idea commonly accepted?

http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm

hi galt, paddlers,
a 15' narrow beam light kayak can be faster than a beamy 17' heavy
kayak.
1.34 x square root of water line length gives the maximum speed of a
displacement hull boat. so longer boats will be faster than shorter boats of
similar designs and materials.
a great practical way to test this theoretical speed is with a gps. i've
recently been doing this with several kayaks (ww and sea kayaks) available
to me, and have found that the formula holds up quite well. but you must
take current and wind into consideration carefully, even silght winds and
currents, as they can result in differences of 0.5 mph to over 1 mph easily.
true fla****er is the most accurate test envorment, but tests with winds and
currents are quite informative also as you see their effects.
a gps is also a great way to test your paddling efficiency. try various
stroke rates, paddle placements, stroke lenghts and see how your speeds are
affected.
al k

Al K wrote:
wrote in message
ups.com...
Is this idea commonly accepted?

http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm

hi galt, paddlers,
a 15' narrow beam light kayak can be faster than a beamy 17' heavy
kayak.
1.34 x square root of water line length gives the maximum speed of a
displacement hull boat. so longer boats will be faster than shorter boats of
similar designs and materials.
a great practical way to test this theoretical speed is with a gps. i've
recently been doing this with several kayaks (ww and sea kayaks) available
to me, and have found that the formula holds up quite well. but you must
take current and wind into consideration carefully, even silght winds and
currents, as they can result in differences of 0.5 mph to over 1 mph easily.
true fla****er is the most accurate test envorment, but tests with winds and
currents are quite informative also as you see their effects.
a gps is also a great way to test your paddling efficiency. try various
stroke rates, paddle placements, stroke lenghts and see how your speeds are
affected.
al k


I think you are right, when I borrow someone's kayak I should have my
gps with me. I borrowed a kayak one evening last week and had the
feeling it was slow but the gps would have offered something more than
a vague feeling.

Al K wrote:

1.34 x square root of water line length gives the maximum speed of a
displacement hull boat.

Hull speed is an arbitrary number that identifies the speed at which the
wavelength of the bow wave is equal to the waterline length of the vessel. It
is not a speed limit of any sort.

http://kayakwiki.org/index.php/Hull_speed

Mike

wrote:

Is this idea commonly accepted?

Interesting site and good information.

However, they have left out something in their comparison of the 15' and 17'
kayaks. What is the displacement used for their calculations? If those numbers
are for the rated displacement of each kayak (or at least a value somewhere
meaningful inside the range for which the kayak is designed), then the
resistance cannot be directly compared. If you put a big paddler, correct for
the big kayak, in the little kayak, it's wetted surface would increase as would
its drag. It may be the case that under those conditions, the overall
resistance of the larger kayak is less. You have to compare them at the same
displacement to compare them equally.

Mike

Michael Daly wrote:
wrote:

Is this idea commonly accepted?

Interesting site and good information.

However, they have left out something in their comparison of the 15' and 17'
kayaks. What is the displacement used for their calculations? If those numbers
are for the rated displacement of each kayak (or at least a value somewhere
meaningful inside the range for which the kayak is designed), then the
resistance cannot be directly compared. If you put a big paddler, correct for
the big kayak, in the little kayak, it's wetted surface would increase as would
its drag. It may be the case that under those conditions, the overall
resistance of the larger kayak is less. You have to compare them at the same
displacement to compare them equally.

Mike

I'm not sure about the loading but he made the argument that one man
trying to paddle a double alone would not gain an advantage from its
extra length. It would actually have more drag.

wrote:

I'm not sure about the loading but he made the argument that one man
trying to paddle a double alone would not gain an advantage from its
extra length. It would actually have more drag.

Then maybe you should have pointed that out. I looked at your subject and
commented on the comparison of the 15' and the 17'. The double is 18'6".

It is widely assumed that longer kayaks are faster. Folks like me are
frequently pointing out that this is not always true. One person in the double
compared to one person in the single shows such an example.

Trying to express the performance of a three-dimensional object in water using a
single parameter will always fail.

Mike

Michael Daly wrote:
wrote:

I'm not sure about the loading but he made the argument that one man
trying to paddle a double alone would not gain an advantage from its
extra length. It would actually have more drag.

Then maybe you should have pointed that out. I looked at your subject and
commented on the comparison of the 15' and the 17'. The double is 18'6".

It is widely assumed that longer kayaks are faster. Folks like me are
frequently pointing out that this is not always true. One person in the double
compared to one person in the single shows such an example.

Trying to express the performance of a three-dimensional object in water using a
single parameter will always fail.

Mike

The 15.5ft boat has the lowest drag on the page. I don't know what he
presumes about loading/displacement.

As Mike points out, one parameter does not make a boat. Drag numbers,
prismatic coefficients and other calculated numbers are only effective
if you are comparing several boats of like type, and also have the
ability to compare the real-world paddling performance of the same boats.
Line up four 17' kayaks (assuming they are the proper size for you) from
different top manufacturers (or kit builders), measure and plot all the
parameters as Vaclav has done here (BTW, I think he infers using the
displacement weight as found on another page in his calculations), and
then paddle each over the same course, same conditions, same heart rate,
and see how the numbers shake out for real world speed, load conditions
and stability.
Now change the course and make it choppier or windier, bigger waves,
etc. I'll bet a dime the numbers fade into oblivion compared to the
feel that certain boats will impart.
Example - from a performance standpoint, the CD Stratus18 is a very fast
boat with very good 'numbers', but it is a handful as a touring boat - I
wouldn't want to be out in a blow on Lake Superior trying to make camp
in that thing. I'd much rather be in a Caribou or Solstice GTS, which
have much worse 'numbers'.

Marsh


wrote:
Michael Daly wrote:
wrote:

I'm not sure about the loading but he made the argument that one man
trying to paddle a double alone would not gain an advantage from its
extra length. It would actually have more drag.
Then maybe you should have pointed that out. I looked at your subject and
commented on the comparison of the 15' and the 17'. The double is 18'6".

It is widely assumed that longer kayaks are faster. Folks like me are
frequently pointing out that this is not always true. One person in the double
compared to one person in the single shows such an example.

Trying to express the performance of a three-dimensional object in water using a
single parameter will always fail.

Mike

The 15.5ft boat has the lowest drag on the page. I don't know what he
presumes about loading/displacement.