On 31-May-2004, (William R. Watt) wrote:

..For a constant displacement, wetted surface area
changes directly with length. Why complicate things?

because it's not true

I give up.

I suspect the subject has been studied by, say,
Soviet sports scientists, but they are not sharing their data.

There are lots of studies that have been published on racing canoes
and kayaks (Olympic class), but you'd probably question their relevance
to recreational canoes.

Mike

Winters' current website is www.greenval.com. The graph of resistance vs
speed is gone. He now has resistance vs speed-to-length ratio which is a
way to include length in the graph. From a quick look today it's still not
clear whether the data is for canoes or kayaks. I'll try to get back to
the library and copy some data points, also see if I can copy the
greatlakeskayaker data. It may be a while before I get around to redoing
the calculations with this data. In the meantime the best we have is a 7%
increase in effort due to hull scratches.




--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

On 31-May-2004, (William R. Watt) wrote:

also see if I can copy the greatlakeskayaker data.

That's my website and the data was taken from Sea Kayaker magazine
(Kaper results) or from:

http://www.unold.dk/paddling/articles/kayakvelocity.html

which appears to be from SK's Broze/Taylor results. Kaper is John
Winter's old resistance program and has a factor for plastic kayaks
among other things. It's now a public domain algorithm and John
told me he no longer uses it, since a commercial product (can't
remember the name) is more useful for him.

BTW, the following figure shows what I explained in a previous post
but which you claimed was not correct.

http://www.greenval.com/fig3_1.gif

Mike

I found what I was looking for at www.greenval.com/winters.html.
Writing about canoe design for frictional resistance John Winter says ...

"A 5% decrese in wetted surface is worth bragging about, but a
single year's scratches and banging can easily double coefficient
of friction from 0.004 on a new fibreglass canoe to 0.008. This
more than offsets the designer's efforts. The cavalier attitude of
most canoeists towards their boats is evidence that a 50%
resistance increase is not often noticed if only because the onset
of its effect is so gradual."

Earlier I wrote in this online discussion that paddling in a group
would require extra effort to keep up with other members who were
in similar boats with smooth hulls. I only assumed a 10% increase
in frictional resistance. Winters implies a 50% increase is not
unusual. I used performance data from Winters' former website. All
Winters data applies to canoes (at one point he mentions a
"typical" 16 foot canoe) and is provided to illustrate the
principles he is writing about. Its not specific to any boat,
particularly not kayaks.

I was kicked off the computer at the public library after an hour,
but not before taking a look at the kayak data provided by Mike
Daly at http://www.greatlakeskayaker.ca/spee...anceGraphs.htm. I
found the graph very interesting. I've copied down the numbers and
would like to replace the resistance in pounds by the effort in
horsepower when I get a free moment. Of the 5 kayaks, the
Endurance 18 and the Arctic Hawk are equivalent and fastest. I
don't know if they are the same length. However the Nordkapp H20
and the Solstice GT are equivalent and second fastest even though
the Nordkapp is 2 ft longer than the Endurance (if I'm
interpreting the names correctly). Up to a speed of 4 knots all
four of these kayaks are equivalent. The two pairs only begin to
diverge at speeds over 4 knots. The remaining kayak, Sonoma, is
the slowest. Its length is unknown. There is an error in the data
for the Sonoma at the fastest speed, revealed by a sudden change
in its graph. The slowest boat is one for which John Winters
suppled the data and I'm sure it is for a canoe, not a kayak, as
all the Winters data I've seen is for canoes.

Even though the boats I currently paddle are only cheap home made
experimental plywood boats I'm careful not to treat them roughly
and get the hulls scratched and gouged. That is why I was so
disgusted to see the condition of the used rental boats offered at
a recent sale here.

--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

The H20 after the Nordkapps name means "Hatches Two Oval" meaning that both
the front and rear hatches are oval instead of the configuration of the
Nordkapp Jubalee, which had only one (the rear one) hatch oval. Pre 1992 or
93 Nordkapps had only the 7 1/2 inch round hatches

Depending on the year , the Nordkapp ranges from 17 foot 8 inches to about
18 feet




"William R. Watt" wrote in message
...


I found what I was looking for at www.greenval.com/winters.html.
Writing about canoe design for frictional resistance John Winter says ...

"A 5% decrese in wetted surface is worth bragging about, but a
single year's scratches and banging can easily double coefficient
of friction from 0.004 on a new fibreglass canoe to 0.008. This
more than offsets the designer's efforts. The cavalier attitude of
most canoeists towards their boats is evidence that a 50%
resistance increase is not often noticed if only because the onset
of its effect is so gradual."

Earlier I wrote in this online discussion that paddling in a group
would require extra effort to keep up with other members who were
in similar boats with smooth hulls. I only assumed a 10% increase
in frictional resistance. Winters implies a 50% increase is not
unusual. I used performance data from Winters' former website. All
Winters data applies to canoes (at one point he mentions a
"typical" 16 foot canoe) and is provided to illustrate the
principles he is writing about. Its not specific to any boat,
particularly not kayaks.

I was kicked off the computer at the public library after an hour,
but not before taking a look at the kayak data provided by Mike
Daly at http://www.greatlakeskayaker.ca/spee...anceGraphs.htm. I
found the graph very interesting. I've copied down the numbers and
would like to replace the resistance in pounds by the effort in
horsepower when I get a free moment. Of the 5 kayaks, the
Endurance 18 and the Arctic Hawk are equivalent and fastest. I
don't know if they are the same length. However the Nordkapp H20
and the Solstice GT are equivalent and second fastest even though
the Nordkapp is 2 ft longer than the Endurance (if I'm
interpreting the names correctly). Up to a speed of 4 knots all
four of these kayaks are equivalent. The two pairs only begin to
diverge at speeds over 4 knots. The remaining kayak, Sonoma, is
the slowest. Its length is unknown. There is an error in the data
for the Sonoma at the fastest speed, revealed by a sudden change
in its graph. The slowest boat is one for which John Winters
suppled the data and I'm sure it is for a canoe, not a kayak, as
all the Winters data I've seen is for canoes.

Even though the boats I currently paddle are only cheap home made
experimental plywood boats I'm careful not to treat them roughly
and get the hulls scratched and gouged. That is why I was so
disgusted to see the condition of the used rental boats offered at
a recent sale here.

--
--------------------------------------------------------------------------
----
William R Watt National Capital FreeNet Ottawa's free community
network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

On 1-Jun-2004, (William R. Watt) wrote:

The remaining kayak, Sonoma, is
the slowest. Its length is unknown. There is an error in the data
for the Sonoma at the fastest speed, revealed by a sudden change
in its graph.

The Sonoma is 13.5 ft long. It does appear that the data is suspect
at the top end.

Mike

wait just a darned minute, are you saying the data you presented is not
test data but is calculated from dimensions using Winter's KAPER model?
that's not data. sorry, it doesn't count as data. it doesn't support your
case. I've used Winters' KAEPER model on one of my own boats for fun btu
it's nto measured data, just calculated numbers. I also calculate numbers
with two hull design programs but they are not the same as measurements
from actual in the water tests.

Michael Daly" ) writes:

That's my website and the data was taken from Sea Kayaker magazine
(Kaper results) or from:

http://www.unold.dk/paddling/articles/kayakvelocity.html

which appears to be from SK's Broze/Taylor results. Kaper is John
Winter's old resistance program and has a factor for plastic kayaks
among other things. It's now a public domain algorithm and John
told me he no longer uses it, since a commercial product (can't
remember the name) is more useful for him.

BTW, the following figure shows what I explained in a previous post
but which you claimed was not correct.

http://www.greenval.com/fig3_1.gif

I've seen it. I'm familiar with it. It does not.



--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

expanding on what I typed in haste yesterday ...

William R. Watt ) writes:

...I also calculate numbers
with two hull design programs but they are not the same as measurements
from actual in the water tests.

I wrote a computer program which, like KAPER, accepts dimensions and
calauclates areas, volumes, and other numbers. Unlike KAEPER this program
uses analystical geometry to do its calcuations. My program is only for
flat bottom skiffs. It was inspired by a clever geomertical analysis of
teh dory hull by Barend Migchelsen of Dorval, Quebec who developed an
simple, elegant method of designing and buidling dories based on geometry.
This appreoach is pretty accurate. The program I wrote produces a tabel of
offsets which is the usual way boat hulls are described for computer
analysis and for boatbuiling. However, whe I input a table of offsets from
my program into the two hull design program I use there is quite a
variation in the areas (wetted surface) and volumes (displacement)
displayed by all three programs. The bigger the boat the more they
diverge. From 7% on a 12 ft skiff to 17% on a 20 footer. the
discrepenciews arise from the different assumtions and formuale used by
the different programs, adn by the way the two hull design programs accept
teh data. they both interpolate between stations and the both produce
different numbers depending on which order you type in the stations.

The program I wrote is on my website under Boats and Design. It is not in
the public domain but it is open source. Anybody can use it an modify it
so long as they don't attempt to sell the result.

So what I'm saying is design numbers are only a guide to boatbuilding. To
verify the numbers you have to test the boat and collect data. I've always
assumed that Winters' numbers were test data. I've also assumed his KAEPER
program was verified against test data. Often a scaled down model is
tested in a tank but even then there are assumptions made in the scaling
and testing apparatus. I've seen them explained in wind tunnel tests for
sails as well. Failures result when the design, despite teh best efforts,
is not good, and there are failures in real life, some quite expensive.
I'm sure some canoe and kayak designs are not very good despite the use of
computers.

BTW, the following figure shows what I explained in a previous post
but which you claimed was not correct.

http://www.greenval.com/fig3_1.gif

I've seen it. I'm familiar with it. It does not.

in your previous post you claimed minimal total hull resistance occurs
when the frictional and wave-making resistance are equal. if you'll notice
on the graph the minimal total resistance occurs when the frictional
resistance is about 1.5 lb and the wave-making resistance is 4.5 lb. There
is a local minimum but it's not the simple intuitive tradeoff you've
claimed.


--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

Kayaks should be designed around people instead of designing for
isolated boat performance. I don't know of any kayak designers who
do this. Instead of concentrating on hull resistance, designers
could concentrate on paddler horsepower requirement. A low cost,
mass marketed kayak should be designed to suit a range of
horsepowers, paddler weights, and paddler dimensions. A kayak
produced for a more limited market can be designed to suit a
smaller range of horespowers, paddler weights, and paddler
dimensions. An expensive one off kayak can be custom designed to
suit the power, weight, and dimensions of an individual paddler.
It would cost no more to custom design a plywood kayak built with
computer cut panels than to design a mass produced plywood kayak
built with computer cut panels. The design ranges should be listed
in the sales information for each model of kayak. Design
performance graphs could be included, and for some boats actual
test data plotted. Such an approach to designing would answer the
buyer's perrenial question "which kayak is right for me?". The
approach is particulary appropriate for kayaks because they are
are primarily transporters of people using the person's own power
resources for propulsion. The cost of the design is small compared
to the cost of materials, labour, distribution, marketing, and
sales. It would not cos much to do a more complete job of the design
and provide better information for the buyer.
--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

William R. Watt wrote:

Kayaks should be designed around people instead of designing for
isolated boat performance. I don't know of any kayak designers who
do this. Instead of concentrating on hull resistance, designers
could concentrate on paddler horsepower requirement. A low cost,
mass marketed kayak should be designed to suit a range of
horsepowers, paddler weights, and paddler dimensions. A kayak
produced for a more limited market can be designed to suit a
smaller range of horespowers, paddler weights, and paddler
dimensions.

That's exactly what the boats currently on the market do, it's just not
expressed in terms of horsepower, since the average paddler wouldn't
have a clue as to what that means.

An expensive one off kayak can be custom designed to
suit the power, weight, and dimensions of an individual paddler.

OK. One can build a custom boat and there are companies that will do so.

It would cost no more to custom design a plywood kayak built with
computer cut panels than to design a mass produced plywood kayak
built with computer cut panels.

How do you figure that? The most efficient hulls (least wetted surface
for a given displacement) are rounded in shape, which cannot be built
from flat panels. The cost to produce a mold for a one-off design is
prohibitive. One could have a boat custom designed and strip built, but
how many people are going to pay in excess of $5000 for a kayak?

The design ranges should be listed
in the sales information for each model of kayak. Design
performance graphs could be included, and for some boats actual
test data plotted.

To what end? This information is often available for racing boats -
where the paddler actually cares about such things - but do you honestly
think that the average recreational or touring paddler would have any
interest in this whatsoever? I'll bet most of them don't even read the
owner's manual, let alone a bunch of technical data that they don't
understand.

Such an approach to designing would answer the
buyer's perrenial question "which kayak is right for me?".

Not if they don't understand the information. Most won't and they're not
going to be willing to learn about hydrodynamics in order to do so.

The
approach is particulary appropriate for kayaks because they are
are primarily transporters of people using the person's own power
resources for propulsion. The cost of the design is small compared
to the cost of materials, labour, distribution, marketing, and
sales. It would not cos much to do a more complete job of the design
and provide better information for the buyer.

Perhaps so, but whatever money it did cost would be largely wasted,
since most paddlers are more interested in the color of their boat than
performance graphs. I think it's safe to say that the vast majority of
kayaks are purchased based on:

- Impulse. One sees a cheap rec boat at one of the Marts or wholesale
clubs and buys it

- Recommendations of a salesman. One goes to a sporting goods store or a
local kayak dealer and buys what they suggest.

- Recommendations of friends. One speaks with friends who are paddlers
and takes their advice.

- What's available in the area. Not all boats have dealers in every
area. Locally made products or those carried by local dealers will
predominate, regardless of whether they're the best boats for specific
paddlers. Few people will special order a boat and pay to have it
shipped to them. While there are a few niche manufacturers that cater to
this market, I'll wager that their combined annual output is less than
2000 boats out of a market of over 300,000.

While you and I and some others here may care about performance data,
it's pretty obvious that most kayak owners don't and never will.