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.