Fiberglass vs plastic
 

Here are the data from the graph on the John Winters website.

"knots" is speed through the water in a dead calm,
a knot is 15% more than a mph
"friction" is hull surface friction resistance
"wave" is hull wave making resistance
"total" is the sum of the two kinds of hull resistance
"hp" is the horsepower needed to sustain that speed at that total resistance

knots: 2 2.6 3 3.5 4 4.6 5 5.5 6
lb friction: 2 2.5 2.75 4 4.75 5 7 8 9
lb wave: 0 0 0 .05 0.75 3 7 15 20
lb total: 2 2.5 2.75 4.5 5.5 8 14 23 29
================================================== =========
hp: .01 .02 .03 .05 .07 .10 .20 .40 .53


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Fiberglass vs plastic
 

On 30-May-2004, (William R. Watt) wrote:

Skin friction does not increase monotonically with length. It does
increase monotonically with the product of surface smoothness and wetted
surface area

If surface smoothness is constant, then skin friction increases monotonically
with wetted surface area. Why would you assume that surface smoothness is
variable among kayaks? For a constant displacement, wetted surface area
changes directly with length. Why complicate things?

Winters' website

His website has been gone for quite a while. I have no way to verify your
interpretations of what he wrote there.

I would like to see data specific to sea
kayaks. the wind and wave resistance data is from a book on sea kayak
cruising. it also appears to me to be pretty general.

In his book, he specifically states that there is no significant difference
in the behavior of canoe and kayak hulls. They come in the same range of
lengths and vary only in width. Most of the other parameters, such as block
and prismatic coefficients are in the same ballpark as well.

Most data is from smooth water conditions. There isn't much data on kayaks
in cruising conditions - that gets really complicated from the standpoint of
analysis, since kayaks operate in rough conditions where simple analysis
breaks down. However, it seems like most decent smooth water designs will
perform adequately in rough conditions, while a poor design in smooth
water is poor in rough. Most kayaks that perform well in smooth water but not
in rough suffer from other problems, such as weathercocking and tracking, not
so much from resistance to forward motion.

Mike

Fiberglass vs plastic
 

On 30-May-2004, (William R. Watt) wrote:

Where on earth do you get that breakdown? Friction resistance
80 times wave resistance?

"Winter's" data at hull speed and total resitance equal to 1/20 hp.
ie the data graphed on Winter's web site.

From your other message:

knots: 2 2.6 3 3.5 4 4.6 5 5.5 6
lb friction: 2 2.5 2.75 4 4.75 5 7 8 9
lb wave: 0 0 0 .05 0.75 3 7 15 20
lb total: 2 2.5 2.75 4.5 5.5 8 14 23 29
================================================== =========
hp: .01 .02 .03 .05 .07 .10 .20 .40 .53

Take a look at the data when you get into the 0.1-0.25hp range.
The lower hp is for the fit paddler and the upper is for the serious
competitor. In this range, the skin friction and wave resistance is
of the same order of magnitude [ (3,5), (7,7) ]. The hull is designed
for use in that speed/power range - upwards of 4.6 kt ( 8.5 kph) That's
a bit faster than I can paddle my kayak for an hour.

If a person is routinely paddling at 3-3.5 kt, they could use a shorter
kayak and not get as much skin friction and still not be pushing waves
around much. It would be easier to paddle and more maneouverable to boot.

The problem with your analysis is that 1/20 hp is low for a fit person.
Also, this data is suspect - most kayaks in the Sea Kayaker reviews are
not in this range. For a recent review of the Solstice GT:

Speed 2.0 3.0 4.0 4.5 5.0 6.0 (kt)
Solstice GT 0.96 2.01 3.66 5.31 8.06 14.23 (lb)

As you can see, the data you provide is quite a bit higher than what the
Solstice shows. Here's some mo

http://www.greatlakeskayaker.ca/speedVsResistanceGraphs.htm
(I make no promises whether this web page will show in anything other
than Internet Explorer - sorry, it's an exported Excel spreadsheet page).

Elite paddlers can put out about 0.3 hp. A fit recreational paddler
can put out about 0.08 to 0.1 hp.

according to teh data on Winters' webiste you you have just
destroyed your earlier argument. at less than 1/20 hp the "boat" (canmoe
or kayak or whatever Winters' data represents) is harldy moving at all.

??? 3.5 kt isn't "hardly moving". I'm not sure what earlier argument I
destroyed. You'll have to be more specific.

Mike

Fiberglass vs plastic
 

"Michael Daly" ) writes:

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

because it's not true

In his book, he specifically states that there is no significant difference
in the behavior of canoe and kayak hulls. They come in the same range of
lengths and vary only in width. Most of the other parameters, such as block
and prismatic coefficients are in the same ballpark as well.

yes, compared to oil tankers, canoes and kayaks are in the same ballpark.
but compared to each other and relative to the low power source, canoes
and kayaks differ in performance. in my experience kayaks are faster than
canoes, their main attraction as far as I can tell. a lot of money goes
into advertising the differences among canoes and kayaks. I would like to
see more precise data. I suspect the subject has been studied by, say,
Soviet sports scientists, but they are not sharing their data.




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Fiberglass vs plastic
 

"Michael Daly" ) writes:

Also, this data is suspect - most kayaks in the Sea Kayaker reviews are
not in this range. For a recent review of the Solstice GT:

Speed 2.0 3.0 4.0 4.5 5.0 6.0 (kt)
Solstice GT 0.96 2.01 3.66 5.31 8.06 14.23 (lb)

As you can see, the data you provide is quite a bit higher than what the
Solstice shows. Here's some mo

http://www.greatlakeskayaker.ca/speedVsResistanceGraphs.htm
(I make no promises whether this web page will show in anything other
than Internet Explorer - sorry, it's an exported Excel spreadsheet page).

thanks. I'll take a look.
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Fiberglass vs plastic
 

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

Fiberglass vs plastic
 

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.




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Fiberglass vs plastic
 

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

Fiberglass vs plastic
 

William R. Watt wrote:
in my experience kayaks are faster than
canoes, their main attraction as far as I can tell.

While this is certainly what attracts some kayakers, I'd say the main
attractions vs. canoes are the kayaks inherent seaworthiness and it's
ability to handle a broad rain of weather and water conditions with
aplomb. Kayaks make paddling in rough condition not only possible, but
fun. I don't see many canoeists paddling in 3'-4'+ seas or 15-20+ knot
winds (actually, I've never seen any), but it's a blast in a kayak. The
same boat can be used for a quiet, relaxing cruise around an estuary to
snap a few nature photos. Although I've seen photos of canoeists playing
in surf, I've never seen anyone do it, but we do it all the time in kayaks.

Of course, I'm talking about sea kayaks, rather than recreational or
whitewater boats. I'm also leaving out the class of boats like the
Kruger "canoes", which are canoes in name only and have more in common
with kayaks.

Fiberglass vs plastic
 

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.

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