Brian Nystrom ) writes:
William R. Watt wrote:

That may not be a
problem for knocking about on your own but if you are on a trip with a
group and their hulls are smooth you are easily paddling 10% more to keep
up.

Exactly where did that figure come from? The tests I've seen indicate
that scratched hulls have ~2-5% more drag smooth hulls, with badly
scarred plastic hulls with lots of "hairies" being at the high end. The
difference with fiberglass boats is minuscule.

the reference is long gone. it said one season's scratches add 5% to
hull resistance.


That's like paddling 11 hours to their 10.

No, it's not like that at all. Even if your 10% figure is correct, it
pertains only to surface friction on the hull. That's only one component
of the total drag that must be overcome by the paddler. Wind resistance
and especially wave making resistance can be very substantial components
of total drag, depending on boat speed and weather conditions.
Realistically, a scratched hull will require you to paddle ~1-2% harder
than a smooth one. Unless you're racing, you'll never notice the difference.

where does that 1-2% figure come from?

at sustained (cruising) paddling speeds hull resistance is still the
biggest component of total hull drag when comparing identical boats. there
are some numbers in a file on my website under "Boats" on average hull,
wind, and wave resistance, and energy consumption. a paddler can't put out
the power needed to maintain high wave making resistance speeds for any
length of time. it's a concern for racers. your point about wind and wave
resistance is well taken. however, considering the money spent on paddles
to reduce effort, the scratches on the hull matter. I don't think 10% is
out of order in anything less than rough conditions. I was trying to be
conservative. I don't have figures for paddlers but cruising sailors
experince moderate conditions most of the time. Rough conditions most of
the time would pretty well eliminate such passtimes as paddling and
sailing.




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Alex McGruer ) writes:

There remains the ugly fact , you are going to have to bring that boat
ashore and sometimes a host of issues will make you follow the wave
ashore and land on a beach. Most rocks will be rounded but it is
still a bump.

Got me there. All my paddling is on lakes and rivers with no swells
or surf, and in open boats which are easier to get in and out of.
I can see where Kayaks would present special problems.

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On 28-May-2004, (William R. Watt) wrote:

at sustained (cruising) paddling speeds hull resistance is still the
biggest component of total hull drag when comparing identical boats. there
are some numbers in a file on my website under "Boats" on average hull,
wind, and wave resistance, and energy consumption. a paddler can't put out
the power needed to maintain high wave making resistance speeds for any
length of time.

Nowhere on your website could I find info to support this. You simply
claim that wave making resistance is not significant at paddling speeds.
For a kayak designed for optimal length at its cruising speed, skin
resistance and wave resistance are roughly equal.

If a paddler is routinely using a kayak under conditions where skin friction
dominates, they'd be better off using a shorter kayak. If they are routinely
pushing against wave-making resistance, they should get a longer kayak.

I don't think 10% is out of order in anything less than rough conditions.

You're still talking thru your hat, Willy. Unless you can cough up a valid
reference, I'll go with Brian's numbers.

Rough conditions most of
the time would pretty well eliminate such passtimes as paddling and
sailing.

You should get out more. Rough conditions are when kayaking gets interesting.
The fact is that kayaks are used in rough conditions (as would be defined by
marine architects) _most_ of the time.

Mike

"Michael Daly" ) writes:
On 28-May-2004, (William R. Watt) wrote:

at sustained (cruising) paddling speeds hull resistance is still the
biggest component of total hull drag when comparing identical boats. there
are some numbers in a file on my website under "Boats" on average hull,
wind, and wave resistance, and energy consumption. a paddler can't put out
the power needed to maintain high wave making resistance speeds for any
length of time.

Nowhere on your website could I find info to support this.

look under Boats, Paddling, first item (Speed, Resistance, Energy).
I'd appreciate seeing more specific data.

You simply
claim that wave making resistance is not significant at paddling speeds.
For a kayak designed for optimal length at its cruising speed, skin
resistance and wave resistance are roughly equal.

I think you mean "wave making resistance". If you have a source for speed and
hull resistance numbers I'd appreciate seeing it. Wind and wave resistance
would be even better.


If a paddler is routinely using a kayak under conditions where skin friction
dominates, they'd be better off using a shorter kayak. If they are routinely
pushing against wave-making resistance, they should get a longer kayak.

Sorry it's not an inverse relation.


I don't think 10% is out of order in anything less than rough conditions.

You're still talking thru your hat, Willy. Unless you can cough up a valid
reference, I'll go with Brian's numbers.

Brian didn't provide any data. You can work it out from the data on my
website. I'd be interested in seeing more precise data than what I have. I
could only find generalizations at the time.


You should get out more. Rough conditions are when kayaking gets interesting.
The fact is that kayaks are used in rough conditions (as would be defined by
marine architects) _most_ of the time.

And where do you get that data, in your dreams?


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William R. Watt wrote:

Brian Nystrom ) writes:

William R. Watt wrote:


That may not be a
problem for knocking about on your own but if you are on a trip with a
group and their hulls are smooth you are easily paddling 10% more to keep
up.

Exactly where did that figure come from? The tests I've seen indicate
that scratched hulls have ~2-5% more drag smooth hulls, with badly
scarred plastic hulls with lots of "hairies" being at the high end. The
difference with fiberglass boats is minuscule.


the reference is long gone. it said one season's scratches add 5% to
hull resistance.

And how was that determined? What exactly constitutes "one season's
scratches"? Though I don't doubt that you have a source for this
information, I have to wonder about the accuracy of such generalities.
It sounds a lot more like opinion than fact.

That's like paddling 11 hours to their 10.

No, it's not like that at all. Even if your 10% figure is correct, it
pertains only to surface friction on the hull. That's only one component
of the total drag that must be overcome by the paddler. Wind resistance
and especially wave making resistance can be very substantial components
of total drag, depending on boat speed and weather conditions.
Realistically, a scratched hull will require you to paddle ~1-2% harder
than a smooth one. Unless you're racing, you'll never notice the difference.


where does that 1-2% figure come from?

It's roughly half of what the test I saw indicated for hull drag.
Wavemaking resistance is no small factor, even at cruising speed. Add
wind resistance and the effect of scratches becomes even less significant.

at sustained (cruising) paddling speeds hull resistance is still the
biggest component of total hull drag when comparing identical boats.

That's simply not true. For a kayak, suface drag is relatively small.
Kayaks are typically paddled pretty close to their theoretical hull
speed. A typical 17' kayak will have a theoretical hull speed of ~5-5.25
knots and will probably be paddled at ~3.5-4 knots regularly. At least
that's true of my boats. At that speed, wavemaking drag is the major
drag component. One can readily feel the exponential increase in output
necessary to incrementally increase speed.

there
are some numbers in a file on my website under "Boats" on average hull,
wind, and wave resistance, and energy consumption. a paddler can't put out
the power needed to maintain high wave making resistance speeds for any
length of time.

I realize that, but it doesn't mean that wave making resistance isn't
the major component of the total drag.

it's a concern for racers. your point about wind and wave
resistance is well taken. however, considering the money spent on paddles
to reduce effort, the scratches on the hull matter.

IMO, the emphasis on ultralight paddles is misplaced. I get less
fatigued from paddling with a 30 oz. Greenland stick than with 24 oz. Euro.

I don't think 10% is
out of order in anything less than rough conditions. I was trying to be
conservative. I don't have figures for paddlers but cruising sailors
experince moderate conditions most of the time. Rough conditions most of
the time would pretty well eliminate such passtimes as paddling and
sailing.

Are you kidding? Fla****er paddling is boring, unless the point is just
to relax and take in the view. My boats come into their own when the
conditions get a bit rough. Rough water is exhilarating! Wind and waves
are where it's at!

Perhaps that's the difference between kayakers and a canoeists? We
apparently have very different perspectives based on what we do on the
water.

William R. Watt ) writes:
"Michael Daly" ) writes:
On 28-May-2004, (William R. Watt) wrote:

at sustained (cruising) paddling speeds hull resistance is still the
biggest component of total hull drag when comparing identical boats. there
are some numbers in a file on my website under "Boats" on average hull,
wind, and wave resistance, and energy consumption. a paddler can't put out
the power needed to maintain high wave making resistance speeds for any
length of time.

Nowhere on your website could I find info to support this.

look under Boats, Paddling, first item (Speed, Resistance, Energy).
I'd appreciate seeing more specific data.


An average person can sustain 1/20 horsepower. When a canoe or
kayak is powered by 1/20 hp in a dead calm the power is overcomimg
4 pounds of hull friction resistance and 0.05 pounds of hull wave
making resistance. If 10% of the friction resistance is due to
scratches, that's 0.4 lb compared to the 0.05 lb wave making
resistance.

Mike wrote he thinks the friction and wave making resistance would
be equal. For that to happen the paddler would have to be
sustaining 1/5 horsepower, or 4 times as much. The boat would be
going almost twice as fast. Athletes can do that. In short bursts
athletes can produce 1/2 hp.

In "Sea Kayaking" J Dowd's data assumes the paddler sustains 0.03
hp. The discrepency likely is due to a different boat being used
at the same speed. In a 10 knot headwind the wind and resulting
waves are producing 0.01 hp.

If hull scratches increase friction resistance by 10%, the paddler
has to produce 10% more hp to overcome it and keep the boat moving
at the same speed in a dead calm. In a 10 knot headwind the
extra power drops to about 7% of the total paddler output.
More precise data than what I have available could affect the
result.


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On 28-May-2004, (William R. Watt) wrote:

If a paddler is routinely using a kayak under conditions where skin friction
dominates, they'd be better off using a shorter kayak. If they are routinely
pushing against wave-making resistance, they should get a longer kayak.

Sorry it's not an inverse relation.

??? The more you say about small craft hydrodynamics, the more I realize
how little you understand.

Skin friction increases with length, while wave-making resistance decreases
with length. Minimum total resistance is where the sum of the two is minimum.
For a given displacement, this occurs when the two are roughly equal. This
will also yield the optimum length for a given velocity at that displacement.

If you paddle where skin friction dominates, that means the kayak is too long.
If you paddle where wave making resistance dominates, the kayak is too short.

I don't think 10% is out of order in anything less than rough conditions.

You're still talking thru your hat, Willy. Unless you can cough up a valid
reference, I'll go with Brian's numbers.

Brian didn't provide any data.

He said 2% or so.

You can work it out from the data on my
website. I'd be interested in seeing more precise data than what I have. I
could only find generalizations at the time.

You have no such data that I've seen. Where do you have the data that indicates
how much resistance is due to scratches?

You should get out more. Rough conditions are when kayaking gets interesting.
The fact is that kayaks are used in rough conditions (as would be defined by
marine architects) _most_ of the time.

And where do you get that data, in your dreams?

"The Shape of the Canoe" by John Winters.

Mike

On 28-May-2004, (William R. Watt) wrote:


An average person can sustain 1/20 horsepower. When a canoe or
kayak is powered by 1/20 hp in a dead calm the power is overcomimg
4 pounds of hull friction resistance and 0.05 pounds of hull wave
making resistance.

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

How can you make such a claim without any reference to the dimensions
of the kayak or canoe? Are you trying to suggest that my WW kayak
has the same resistance as my sea kayak?

Mike wrote he thinks the friction and wave making resistance would
be equal. For that to happen the paddler would have to be
sustaining 1/5 horsepower, or 4 times as much.

Why? where do you get that number?

Athletes can do that. In short bursts athletes can produce 1/2 hp.

Cyclists can put out those kinds of power levels. However, if you're
not using your legs, horsepower is harder to generate. Elite paddlers
can put out about 0.3 hp. A fit recreational paddler can put out about
0.08 to 0.1 hp.

Mike

"Michael Daly" ) writes:
On 28-May-2004, (William R. Watt) wrote:


Sorry it's not an inverse relation.

??? The more you say about small craft hydrodynamics, the more I realize
how little you understand.

Skin friction increases with length, while wave-making resistance decreases
with length. Minimum total resistance is where the sum of the two is minimum.

Skin friction does not increase monotonically with length. It does
increase monotonically with the product of surface smoothness and wetted
surface area. Wetted surface area in a dead calm is a function of
displacement and hull shape but not a well-defined mathematical function,
and it is complicated by waves. There are quite a few indicators of hull
shape such as length-to-beam ratio, block coefficient, prismatic
coefficient, and girth.

Brian didn't provide any data.

He said 2% or so.

A percentage is not data. A percentage is a calculated number.

You have no such data that I've seen. Where do you have the data that indicates
how much resistance is due to scratches?


And where do you get that data, in your dreams?

"The Shape of the Canoe" by John Winters.

the hull resistance data on my website is from Winters' website. where he
got the data I do not know. at one time he was collaborating with a
university in Australia. the fellow at the university has posted in this
newsgroup. Its been a few years and I can't recall the university. the
"Winters" data is very general. 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.

you are not basing your arugment on data, but on your impressions.
I am basing my argument on actual data which I admit is pretty general.

I know what you are trying to express, that within a narrow range
there is a local optimum.
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"Michael Daly" ) writes:
On 28-May-2004, (William R. Watt) wrote:


An average person can sustain 1/20 horsepower. When a canoe or
kayak is powered by 1/20 hp in a dead calm the power is overcomimg
4 pounds of hull friction resistance and 0.05 pounds of hull wave
making resistance.

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.


How can you make such a claim without any reference to the dimensions
of the kayak or canoe? Are you trying to suggest that my WW kayak
has the same resistance as my sea kayak?

as I have pointe out a number of times in this discussion that is
precisely the weakness in the data on Winters'w web site I would like to
see refined. DO YOU HAVE THAT DATA?


Mike wrote he thinks the friction and wave making resistance would
be equal. For that to happen the paddler would have to be
sustaining 1/5 horsepower, or 4 times as much.

Why? where do you get that number?

the data on Winters' webiste.


Athletes can do that. In short bursts athletes can produce 1/2 hp.

Cyclists can put out those kinds of power levels. However, if you're
not using your legs, horsepower is harder to generate. 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.

sorry, numbers don't lie. provided the numbers measure what we want and
I'm sure the numbers on Winters' website measure speed and hull resistance
of a paddled boat, although we don't know exaclty which paddled boat.

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