Some time ago I was told by Vaclav Stejskal of OneOceanKayaks.com that
beyond 17 feet or so longer boats do not provide an efficiency
advantage. Yet we know that surf skis and other racing boats are often
as long as 22ft. After playing with Kayak Foundry, a freeware program
by Ross Leidy (http://www.blueheronkayaks.com/kayak/index.html) I am
seeing the same sort of results that Vaclav Stejskal predicted. Adding
length is not improving the total calculated drag. So what is the
truth of the matter? Is the standard method of calculating drag from a
computer model inaccurate?

http://www.westsideboatshop.com/
http://www.kayakpro.com/kayakpro/www...od_vampire.htm
http://www.sportzhub.com/ruahine/kayaks.htm
http://www.oceanpaddlesports.com/surfskis.html

On Sep 21, 1:59 pm, Davej wrote:
Some time ago I was told by Vaclav Stejskal of OneOceanKayaks.com that
beyond 17 feet or so longer boats do not provide an efficiency
advantage. Yet we know that surf skis and other racing boats are often
as long as 22ft. After playing with Kayak Foundry, a freeware program
by Ross Leidy (http://www.blueheronkayaks.com/kayak/index.html) I am
seeing the same sort of results that Vaclav Stejskal predicted. Adding
length is not improving the total calculated drag. So what is the
truth of the matter? Is the standard method of calculating drag from a
computer model inaccurate?

http://www.westsideboatshop.com/http.../surfskis.html

Take a look at an Epic Endurance
http://www.seakayakermag.com/PDFs/Endurance_stats.pdf

Look at the amount of waterline and wetted surface.

Davej wrote:
Some time ago I was told by Vaclav Stejskal of OneOceanKayaks.com that
beyond 17 feet or so longer boats do not provide an efficiency
advantage. Yet we know that surf skis and other racing boats are often
as long as 22ft. After playing with Kayak Foundry, a freeware program
by Ross Leidy (http://www.blueheronkayaks.com/kayak/index.html) I am
seeing the same sort of results that Vaclav Stejskal predicted. Adding
length is not improving the total calculated drag. So what is the
truth of the matter? Is the standard method of calculating drag from a
computer model inaccurate?

http://www.westsideboatshop.com/
http://www.kayakpro.com/kayakpro/www...od_vampire.htm
http://www.sportzhub.com/ruahine/kayaks.htm
http://www.oceanpaddlesports.com/surfskis.html

For typical non-racers, longer boats offer no advantages, since the
paddler cannot push the boat to it's performance limits and their drag
at lower speeds is higher than that of shorter boats. The lower the
power of the paddler, the less the advantage of longer boats.

OTOH, if you have the horsepower to push a longer boat to its limit and
keep it there, there is a definite advantage. However, the percentage of
paddlers capable of that is tiny.

On Sep 23, 7:13 am, Brian Nystrom wrote:
Davej wrote:
Some time ago I was told by Vaclav Stejskal of OneOceanKayaks.com that
beyond 17 feet or so longer boats do not provide an efficiency
advantage. Yet we know that surf skis and other racing boats are often
as long as 22ft. After playing with Kayak Foundry, a freeware program
by Ross Leidy (http://www.blueheronkayaks.com/kayak/index.html) I am
seeing the same sort of results that Vaclav Stejskal predicted. Adding
length is not improving the total calculated drag. So what is the
truth of the matter? Is the standard method of calculating drag from a
computer model inaccurate?

http://www.westsideboatshop.com/
http://www.kayakpro.com/kayakpro/www...od_vampire.htm
http://www.sportzhub.com/ruahine/kayaks.htm
http://www.oceanpaddlesports.com/surfskis.html

For typical non-racers, longer boats offer no advantages, since the
paddler cannot push the boat to it's performance limits and their drag
at lower speeds is higher than that of shorter boats. The lower the
power of the paddler, the less the advantage of longer boats.

OTOH, if you have the horsepower to push a longer boat to its limit and
keep it there, there is a definite advantage. However, the percentage of
paddlers capable of that is tiny.

Ok, but shouldn't I be able to see the "residual" drag curve become
less steep with an increase in hullspeed, where hullspeed = 1.34 *
Sqrt(water-line-length) ? If not is there a third type of "drag" used
to describe the bow-wave climbing hullspeed effect?

Davej wrote:
On Sep 23, 7:13 am, Brian Nystrom wrote:
Davej wrote:
Some time ago I was told by Vaclav Stejskal of OneOceanKayaks.com that
beyond 17 feet or so longer boats do not provide an efficiency
advantage. Yet we know that surf skis and other racing boats are often
as long as 22ft. After playing with Kayak Foundry, a freeware program
by Ross Leidy (http://www.blueheronkayaks.com/kayak/index.html) I am
seeing the same sort of results that Vaclav Stejskal predicted. Adding
length is not improving the total calculated drag. So what is the
truth of the matter? Is the standard method of calculating drag from a
computer model inaccurate?
http://www.westsideboatshop.com/
http://www.kayakpro.com/kayakpro/www...od_vampire.htm
http://www.sportzhub.com/ruahine/kayaks.htm
http://www.oceanpaddlesports.com/surfskis.html
For typical non-racers, longer boats offer no advantages, since the
paddler cannot push the boat to it's performance limits and their drag
at lower speeds is higher than that of shorter boats. The lower the
power of the paddler, the less the advantage of longer boats.

OTOH, if you have the horsepower to push a longer boat to its limit and
keep it there, there is a definite advantage. However, the percentage of
paddlers capable of that is tiny.

Ok, but shouldn't I be able to see the "residual" drag curve become
less steep with an increase in hullspeed, where hullspeed = 1.34 *
Sqrt(water-line-length) ? If not is there a third type of "drag" used
to describe the bow-wave climbing hullspeed effect?

The drag curve doesn't become less steep, the steep part of the curve
just occurs at a higher speed.

On Sep 24, 5:49 am, Brian Nystrom wrote:
Davej wrote:
On Sep 23, 7:13 am, Brian Nystrom wrote:
Davej wrote:
Some time ago I was told by Vaclav Stejskal of OneOceanKayaks.com that
beyond 17 feet or so longer boats do not provide an efficiency
advantage. Yet we know that surf skis and other racing boats are often
as long as 22ft. After playing with Kayak Foundry, a freeware program
by Ross Leidy (http://www.blueheronkayaks.com/kayak/index.html) I am
seeing the same sort of results that Vaclav Stejskal predicted. Adding
length is not improving the total calculated drag. So what is the
truth of the matter? Is the standard method of calculating drag from a
computer model inaccurate?
http://www.westsideboatshop.com/
http://www.kayakpro.com/kayakpro/www...od_vampire.htm
http://www.sportzhub.com/ruahine/kayaks.htm
http://www.oceanpaddlesports.com/surfskis.html
For typical non-racers, longer boats offer no advantages, since the
paddler cannot push the boat to it's performance limits and their drag
at lower speeds is higher than that of shorter boats. The lower the
power of the paddler, the less the advantage of longer boats.

OTOH, if you have the horsepower to push a longer boat to its limit and
keep it there, there is a definite advantage. However, the percentage of
paddlers capable of that is tiny.

Ok, but shouldn't I be able to see the "residual" drag curve become
less steep with an increase in hullspeed, where hullspeed = 1.34 *
Sqrt(water-line-length) ? If not is there a third type of "drag" used
to describe the bow-wave climbing hullspeed effect?

The drag curve doesn't become less steep, the steep part of the curve
just occurs at a higher speed.

Ok, that is what I meant, but I don't seem to see that in the curves.

It's not so much hull resistence you need to see, but (horse)power
requirement for the speeds plotted along
the bottom of the graph. Then you can judge how fast the boat can go
given your individual power ability.
Over distance the "average" paddler can maintian 1/20 (0.05)
horsepower.

However, calculated hull resistance is only a base measure. On top of
that you have to overcome wind and waves
when they are against you, or add them to your effort when they are
with you.
I attempted to roughly broke these down near the bottom of this page:
www.ncf.ca/~ag384/Boats.htm

On Sep 25, 9:49 am, Wm Watt wrote:
It's not so much hull resistance you need to see, but (horse)power
requirement for the speeds plotted along
the bottom of the graph. Then you can judge how fast the boat can go
given your individual power ability.
Over distance the "average" paddler can maintian 1/20 (0.05)
horsepower.

However, calculated hull resistance is only a base measure. On top of
that you have to overcome wind and waves
when they are against you, or add them to your effort when they are
with you. I attempted to roughly broke these down near the bottom of this
page:www.ncf.ca/~ag384/Boats.htm

Ok, but to restate my issue, I'm trying to understand why the KAPER
curves show no advantage for a longer boat. Of course I'm trusting
that Kayak Foundry is implementing KAPER correctly. As an example I
have two crude designs posted here;

http://home.att.net/~galt_57/b014.yak --- a very slender ~15 ft boat
LWL= 14' 7.4"
http://home.att.net/~galt_57/b022.yak --- a very slender 22 ft boat
LWL= 21' 10.8"

They both have the same 17" waterline beam. Looking at the curves I
can't see anything that hints that the "hull speed" is increased for
the 22 ft design.

On Sep 25, 3:08 pm, Davej wrote:

They both have the same 17" waterline beam. Looking at the curves I
can't see anything that hints that the "hull speed" is increased for
the 22 ft design.

It may not. There is a famous case of two canoe racers who built
themselves a long boat thinking they would leave the competition in
their wake but finished well back because the longer boat weighed
more. They weren't aware of all the effects adding length has on
performance.

I'm sorry I don't have John Winter's KAPER formulae to show how weight
enters the math but you can find some of his writings at www.greenval.com
where canoes are sold from his designs, also some of his publications.
Perhaps the first page of www.greenval.com/shape_part2.html will
explain it, although I regret the KAPER formula does not appear. I've
only used KAPER once to check out a design of a sailboat based on a
canoe I built for myself and cannot find the formulae among my notes.
Also look at part1.html and part3.html for his complete "Shape of the
Canoe". Apparently Green Valley sells an updated edition online which
includes a copy of KAPER.

Most of my boat calculations have been for sail power where
displacement is a big factor. Displacement is the total weigth of both
boat and contents. Canoes and kayaks, being light dispalcement boats,
don't perform the same as sailboats and motorboats. That's why
Winter's modified the formulae.

Hope that helps.

On Sep 25, 5:31 pm, Wm Watt wrote:
On Sep 25, 3:08 pm, Davej wrote:

They both have the same 17" waterline beam. Looking at the curves I
can't see anything that hints that the "hull speed" is increased for
the 22 ft design.

It may not. There is a famous case of two canoe racers who built
themselves a long boat thinking they would leave the competition in
their wake but finished well back because the longer boat weighed
more. They weren't aware of all the effects adding length has on
performance.

I'm sorry I don't have John Winter's KAPER formulae to show how weight
enters the math but you can find some of his writings atwww.greenval.com
where canoes are sold from his designs, also some of his publications.
Perhaps the first page ofwww.greenval.com/shape_part2.htmlwill
explain it, although I regret the KAPER formula does not appear. I've
only used KAPER once to check out a design of a sailboat based on a
canoe I built for myself and cannot find the formulae among my notes.
Also look at part1.html and part3.html for his complete "Shape of the
Canoe". Apparently Green Valley sells an updated edition online which
includes a copy of KAPER.

Most of my boat calculations have been for sail power where
displacement is a big factor. Displacement is the total weigth of both
boat and contents. Canoes and kayaks, being light dispalcement boats,
don't perform the same as sailboats and motorboats. That's why
Winter's modified the formulae.

Hope that helps.

Well, I found out I was not preparing the models correctly. The
waterline has to be manually adjusted before the curves are valid. The
corrected models are;

http://home.att.net/~galt_57/c014.yak
http://home.att.net/~galt_57/c022.yak

And now the long boat has superior drag for all speeds above 4 knots.
As you mentioned this still leaves the problem of constructing a long
boat that is very light weight...