I was following behind this guy about 10 ft for entire race. It took
quite a bit of effort to steer to stay behind him. I tried hard to get
closer but for some reason I couldnt. I guess I could have got behind
someone going slower.

I was in a short adventure race this weekend . There was 4kms of sea
kayaking. I ended up in a soltice gts. The rudder was stuck down so I
had to use rudder. The cockpit was small and i could not move my legs.
My feet were on the pedals but just kind of resting on the pedals. When
I paddle with my small kayak with fixed rudders , I really shove my
feet hard down on pedals.

ace wrote:
I was following behind this guy about 10 ft for entire race. It took
quite a bit of effort to steer to stay behind him. I tried hard to get
closer but for some reason I couldnt. I guess I could have got behind
someone going slower.

I was in a short adventure race this weekend . There was 4kms of sea
kayaking. I ended up in a soltice gts. The rudder was stuck down so I
had to use rudder. The cockpit was small and i could not move my legs.
My feet were on the pedals but just kind of resting on the pedals. When
I paddle with my small kayak with fixed rudders , I really shove my
feet hard down on pedals.

At 10 feet, you were probably sitting on the uphill side of the wave.
In order to effectively draft, you either need to be a little further
back, or a lot further forward. Depending on the actual speed, and the
boats involved, you will usually find you are running into the guy's
rudder unless you slide just a little to the side (which works fine as a
rule). At 1/2 wavelength, you'll be paddling uphill, and actually
working harder than paddling by yourself. A lot of it is just plain
feel and experience, but if you practice riding with another boat,
you'll find it gets easier as time goes on.

The GTS is a tough boat to fit in if you've got big feet or big legs.
That keyhole makes it a little tough. But - you just need to adjust
your technique a bit so that your feet are both pushing against the
pedals and more flexing than actually moving. Tough, I know, but it can
be done. Also, you might try paddling without shoes - just socks. I
know - the beach is a little cold, but you may find you get better fit
under the deck that way. It only takes a few seconds to slip running
shoes or cycling shoes on at the end, but running shoe heels really
cramp your feet in a lot of boats.

Marsh

Thanks! You are a regular gold mine of information. Part of the problem
is that I do most of my training in a 10 ft boat with huge cockpit and
rigid pedals. I'm thinking of getting a mirror on my glasses so I can
see what is happening behind me. I'll have to revise my drafting
procedure.

Marsh Jones wrote:
ace wrote:
I was following behind this guy about 10 ft for entire race. It took
quite a bit of effort to steer to stay behind him. I tried hard to get
closer but for some reason I couldnt. I guess I could have got behind
someone going slower.

I was in a short adventure race this weekend . There was 4kms of sea
kayaking. I ended up in a soltice gts. The rudder was stuck down so I
had to use rudder. The cockpit was small and i could not move my legs.
My feet were on the pedals but just kind of resting on the pedals. When
I paddle with my small kayak with fixed rudders , I really shove my
feet hard down on pedals.

At 10 feet, you were probably sitting on the uphill side of the wave.
In order to effectively draft, you either need to be a little further
back, or a lot further forward. Depending on the actual speed, and the
boats involved, you will usually find you are running into the guy's
rudder unless you slide just a little to the side (which works fine as a
rule). At 1/2 wavelength, you'll be paddling uphill, and actually
working harder than paddling by yourself. A lot of it is just plain
feel and experience, but if you practice riding with another boat,
you'll find it gets easier as time goes on.

The GTS is a tough boat to fit in if you've got big feet or big legs.
That keyhole makes it a little tough. But - you just need to adjust
your technique a bit so that your feet are both pushing against the
pedals and more flexing than actually moving. Tough, I know, but it can
be done. Also, you might try paddling without shoes - just socks. I
know - the beach is a little cold, but you may find you get better fit
under the deck that way. It only takes a few seconds to slip running
shoes or cycling shoes on at the end, but running shoe heels really
cramp your feet in a lot of boats.

Marsh

ace wrote:
I was following behind this guy about 10 ft for entire race. It took
quite a bit of effort to steer to stay behind him. I tried hard to get
closer but for some reason I couldnt. I guess I could have got behind
someone going slower.


Theoretically, if both paddlers and boats are perfectly matched, then
some small variable like wind or bow wave will make the difference.
However you have to ignore the advantage to the following paddler of
following a pace boat until the time comes for the final sprint. In
practice I think no paddlers and boats are perfectly matched.

In more extreme conditions position is important. Other posters have
written of cars and bicycles. When driving from Ottawa to Florida in a
small car, tucking in behind a semi on the I95 and driving in it's slip
stream conserves fuel. You just hope none of the watermellons on those
trailers in the Carolinas fall off the back. Drving from Ottawa to
Vancouver in a small car, trying to pass a semi in a head wind on the
praries my car could not break through the "bow wave". I tried a few
times comming up beside the cab but that was a far as I got. These were
low powered cars, Dodge Colt and Ford Festiva.

As far as paddlers staying together, it's probably because of the steep
gradient on the exponential hull speed curve. Small increments in speed
require large differences in paddler power which cannot be sustained
for long. I'm sure kayaks and canoes can be designed so the curve takes
off at given rates of power, cusomizing the hull to an individual
paddler's strength and endureance. I don't know if anyone actually does
this.

Sailors race under much the same conditions and have developed standard
strategies for competing in close quarters. Winning is as much about
strategy and position as boat speed. Boat speed is a necessary, but not
a sufficient, condition.

Wm Watt wrote:
ace wrote:
I was following behind this guy about 10 ft for entire race. It took
quite a bit of effort to steer to stay behind him. I tried hard to get
closer but for some reason I couldnt. I guess I could have got behind
someone going slower.


Theoretically, if both paddlers and boats are perfectly matched, then
some small variable like wind or bow wave will make the difference.
However you have to ignore the advantage to the following paddler of
following a pace boat until the time comes for the final sprint. In
practice I think no paddlers and boats are perfectly matched.

In more extreme conditions position is important. Other posters have
written of cars and bicycles. When driving from Ottawa to Florida in a
small car, tucking in behind a semi on the I95 and driving in it's slip
stream conserves fuel. You just hope none of the watermellons on those
trailers in the Carolinas fall off the back. Drving from Ottawa to
Vancouver in a small car, trying to pass a semi in a head wind on the
praries my car could not break through the "bow wave". I tried a few
times comming up beside the cab but that was a far as I got. These were
low powered cars, Dodge Colt and Ford Festiva.

As far as paddlers staying together, it's probably because of the steep
gradient on the exponential hull speed curve. Small increments in speed
require large differences in paddler power which cannot be sustained
for long. I'm sure kayaks and canoes can be designed so the curve takes
off at given rates of power, cusomizing the hull to an individual
paddler's strength and endureance. I don't know if anyone actually does
this.

Sailors race under much the same conditions and have developed standard
strategies for competing in close quarters. Winning is as much about
strategy and position as boat speed. Boat speed is a necessary, but not
a sufficient, condition.


Your Festiva example is pretty good for aerodynamic drag and drafting -
and yeah - drafting semis in a Festiva is extreme. We used to do it in
an old VW microbus:-)

Low speed hydrodynamics is also an extreme condition. When you get two
racing boats, or boats racing, that are similar enough in speed and
strength that one doesn't just 'up&leave' drafting happens.

On a smaller scale, it breaks down somewhat. In bicycles, you aren't
moving enough fluid medium (air) to come near 'hull speed' - it's a
matter of how much power you can generate to make the bike go. My
"proof" is that while I can still briefly go 30MPH on the flat, I
can(used to) go 64MPH down a mountain. There is no 'hull speed'
limitation until a bike is moving faster than mere mortals dare tread.

Boats, in a very viscous medium (water) behave quite differently. Water
behaves quite differently from air. Being a business major and all, I
don't have enough strong science to explain all the theory about waves -
my lab is the river/lake. It's pretty easy to get a racing canoe or
reasonably fast kayak to hull speed. And as has been covered here, hull
speed is simply the speed at which the 1st wave period is the same
length as the boat. There is also a second wave, third, forth etc
continuing backwards from the boat. These waves "Vee" away from the
hull at some angle - which is at least partially defined by the shape of
the hull. The amplitude of waves is affected by several factors - shape
and resistance/displacement of the hull, depth of water, and probably a
few that I've left out. It isn't just as simple as calculating a conic
shape with a given displacement. It's how the boat sits in the water at
speed in various conditions, how tapers back in, and how it behaves with
other boats. A USCA Cruiser is the same length and width at the
gunwhale as a Pro canoe, but they have different underwater shapes and
draft very differently.

Drafting on a bike is pretty straightforward. Assuming the same speed
for both bikes, it takes more watts to draft at 20feet back (3 lengths)
than it does at 10, 5, etc. At 6" from the back wheel, you feel like
it's a pretty free ride. In racing boats, the draft is much more
difficult. At 17', you are stuck behind the 2nd wave, and are working
your butt off to get closer, but you can sit at 18' pretty easily and
maintain position unless it gets shallow all of the sudden. If you have
enough strength to punch thru, you can get on the downhill face of the
wave and close quite quickly to the stern ride. This takes some skill
to hold position, because the boat generally wants to wander away from
directly behind (as opposed to bike where the low pressure zone is felt,
and makes it easier to stay there)

However, as the depth goes from infinite (+20') to 4-5 feet, the waves
will shorten and steepen, and you can easily get stuck teetering on top
of a big stern roller and wind up going backwards quickly. This 2-5'
water is known as suckwater to most canoe racers. It sucks to paddle
in, and the stern is 'sucked' down - because you are now paddling up the
hill of your bow wave that's being reflected off the bottom quite
noticeably.

So the next (and usually best) place to be is on the same wave as the
lead boat - side wake. No similar position exists for bikes. Side
waking takes much more experience and work, because you are now
constantly getting sucked in to the other boat or pushed out. In a
canoe, it usually means riding with the bow paddler somewhere around the
center thwart, but different boats and conditions move this up or back.
However, this is about the only successful place from which to mount an
attack, especially in shallow water. Again, it's an empirical sense,
but I think riding the side wake also may increase the effective 'hull
speed' of the two boats together by moving the stern wave peak further
back. [Anybody want to tank test this?]

Popping a canoe or kayak occurs when you get the boat up and over the
bow wave. Done well, drafting can continue here, done poorly and the
poor sucker in back can be walking when they suddenly wind up being
pushed onto the beach or run out of water in the belly of the wave.
Racing canoes love 6" deep sand bottom rivers.

So there's a short and possibly refutable summary of why drafting on a
bike can't directly be compared to drafting/riding in a boat. By all
means, poke holes in it, clarify points, and elaborate on the science.

Marsh

Interesting. You must have majored in accounting or mis. I might buy a
couple small toy boats and work this out in bath tub.

Marsh Jones wrote:
Wm Watt wrote:
ace wrote:
I was following behind this guy about 10 ft for entire race. It took
quite a bit of effort to steer to stay behind him. I tried hard to get
closer but for some reason I couldnt. I guess I could have got behind
someone going slower.


Theoretically, if both paddlers and boats are perfectly matched, then
some small variable like wind or bow wave will make the difference.
However you have to ignore the advantage to the following paddler of
following a pace boat until the time comes for the final sprint. In
practice I think no paddlers and boats are perfectly matched.

In more extreme conditions position is important. Other posters have
written of cars and bicycles. When driving from Ottawa to Florida in a
small car, tucking in behind a semi on the I95 and driving in it's slip
stream conserves fuel. You just hope none of the watermellons on those
trailers in the Carolinas fall off the back. Drving from Ottawa to
Vancouver in a small car, trying to pass a semi in a head wind on the
praries my car could not break through the "bow wave". I tried a few
times comming up beside the cab but that was a far as I got. These were
low powered cars, Dodge Colt and Ford Festiva.

As far as paddlers staying together, it's probably because of the steep
gradient on the exponential hull speed curve. Small increments in speed
require large differences in paddler power which cannot be sustained
for long. I'm sure kayaks and canoes can be designed so the curve takes
off at given rates of power, cusomizing the hull to an individual
paddler's strength and endureance. I don't know if anyone actually does
this.

Sailors race under much the same conditions and have developed standard
strategies for competing in close quarters. Winning is as much about
strategy and position as boat speed. Boat speed is a necessary, but not
a sufficient, condition.


Your Festiva example is pretty good for aerodynamic drag and drafting -
and yeah - drafting semis in a Festiva is extreme. We used to do it in
an old VW microbus:-)

Low speed hydrodynamics is also an extreme condition. When you get two
racing boats, or boats racing, that are similar enough in speed and
strength that one doesn't just 'up&leave' drafting happens.

On a smaller scale, it breaks down somewhat. In bicycles, you aren't
moving enough fluid medium (air) to come near 'hull speed' - it's a
matter of how much power you can generate to make the bike go. My
"proof" is that while I can still briefly go 30MPH on the flat, I
can(used to) go 64MPH down a mountain. There is no 'hull speed'
limitation until a bike is moving faster than mere mortals dare tread.

Boats, in a very viscous medium (water) behave quite differently. Water
behaves quite differently from air. Being a business major and all, I
don't have enough strong science to explain all the theory about waves -
my lab is the river/lake. It's pretty easy to get a racing canoe or
reasonably fast kayak to hull speed. And as has been covered here, hull
speed is simply the speed at which the 1st wave period is the same
length as the boat. There is also a second wave, third, forth etc
continuing backwards from the boat. These waves "Vee" away from the
hull at some angle - which is at least partially defined by the shape of
the hull. The amplitude of waves is affected by several factors - shape
and resistance/displacement of the hull, depth of water, and probably a
few that I've left out. It isn't just as simple as calculating a conic
shape with a given displacement. It's how the boat sits in the water at
speed in various conditions, how tapers back in, and how it behaves with
other boats. A USCA Cruiser is the same length and width at the
gunwhale as a Pro canoe, but they have different underwater shapes and
draft very differently.

Drafting on a bike is pretty straightforward. Assuming the same speed
for both bikes, it takes more watts to draft at 20feet back (3 lengths)
than it does at 10, 5, etc. At 6" from the back wheel, you feel like
it's a pretty free ride. In racing boats, the draft is much more
difficult. At 17', you are stuck behind the 2nd wave, and are working
your butt off to get closer, but you can sit at 18' pretty easily and
maintain position unless it gets shallow all of the sudden. If you have
enough strength to punch thru, you can get on the downhill face of the
wave and close quite quickly to the stern ride. This takes some skill
to hold position, because the boat generally wants to wander away from
directly behind (as opposed to bike where the low pressure zone is felt,
and makes it easier to stay there)

However, as the depth goes from infinite (+20') to 4-5 feet, the waves
will shorten and steepen, and you can easily get stuck teetering on top
of a big stern roller and wind up going backwards quickly. This 2-5'
water is known as suckwater to most canoe racers. It sucks to paddle
in, and the stern is 'sucked' down - because you are now paddling up the
hill of your bow wave that's being reflected off the bottom quite
noticeably.

So the next (and usually best) place to be is on the same wave as the
lead boat - side wake. No similar position exists for bikes. Side
waking takes much more experience and work, because you are now
constantly getting sucked in to the other boat or pushed out. In a
canoe, it usually means riding with the bow paddler somewhere around the
center thwart, but different boats and conditions move this up or back.
However, this is about the only successful place from which to mount an
attack, especially in shallow water. Again, it's an empirical sense,
but I think riding the side wake also may increase the effective 'hull
speed' of the two boats together by moving the stern wave peak further
back. [Anybody want to tank test this?]

Popping a canoe or kayak occurs when you get the boat up and over the
bow wave. Done well, drafting can continue here, done poorly and the
poor sucker in back can be walking when they suddenly wind up being
pushed onto the beach or run out of water in the belly of the wave.
Racing canoes love 6" deep sand bottom rivers.

So there's a short and possibly refutable summary of why drafting on a
bike can't directly be compared to drafting/riding in a boat. By all
means, poke holes in it, clarify points, and elaborate on the science.

Marsh

Marsh Jones wrote:

On a smaller scale, it breaks down somewhat. In bicycles, you aren't
moving enough fluid medium (air) to come near 'hull speed' - it's a
matter of how much power you can generate to make the bike go. My
"proof" is that while I can still briefly go 30MPH on the flat, I
can(used to) go 64MPH down a mountain. There is no 'hull speed'
limitation until a bike is moving faster than mere mortals dare tread.

On a bike, the force due to wind resistance increases with the square of the
velocity. Add to that the rolling and friction resistance and the overall
effect is pretty much the same as resistance felt by a boat in water. Take a
look at the drag versus velocity characteristics of a boat and note the somewhat
arbitrary point chosen for "hull speed". Try Marchaj's "Sailing Theory and
Practice" at your library. Then compare it to a graph of total resistance
versus velocity for a bike and see if you can find a meaningful difference.

If you want to see a kayak or canoe move faster than hull speed without a lot of
paddle effort, try surfing a big wave. That's just like riding a bike downhill.

Boats and bikes pretty much follow the same behavior. Both are moving in fluids
and whether air or water, the physics is the same.

So there's a short and possibly refutable summary of why drafting on a bike
can't directly be compared to drafting/riding in a boat.

I promise not to write about business if you stop making up physics. :-)

Mike

"On a bike, the force due to wind resistance increases with the square
of the
velocity. "

Would this be true for different atomospheric pressures? Is this a
rough rule of thumb? I dont see how there can be such a tidy formula
for something as variable as air. what if air was replaced by carbon
dioxide.

ace wrote:

Would this be true for different atomospheric pressures? Is this a
rough rule of thumb? I dont see how there can be such a tidy formula
for something as variable as air. what if air was replaced by carbon
dioxide.


The formula applies for any gas, any density. Check any book on fluid mechanics
or aerodynamics or Wikipedia: http://en.wikipedia.org/wiki/Drag_%28physics%29.

Mike

Michael Daly wrote:
Marsh Jones wrote:

On a smaller scale, it breaks down somewhat. In bicycles, you aren't
moving enough fluid medium (air) to come near 'hull speed' - it's a
matter of how much power you can generate to make the bike go. My
"proof" is that while I can still briefly go 30MPH on the flat, I
can(used to) go 64MPH down a mountain. There is no 'hull speed'
limitation until a bike is moving faster than mere mortals dare tread.

On a bike, the force due to wind resistance increases with the square of
the velocity. Add to that the rolling and friction resistance and the
overall effect is pretty much the same as resistance felt by a boat in
water. Take a look at the drag versus velocity characteristics of a
boat and note the somewhat arbitrary point chosen for "hull speed". Try
Marchaj's "Sailing Theory and Practice" at your library. Then compare
it to a graph of total resistance versus velocity for a bike and see if
you can find a meaningful difference.

If you want to see a kayak or canoe move faster than hull speed without
a lot of paddle effort, try surfing a big wave. That's just like riding
a bike downhill.

Boats and bikes pretty much follow the same behavior. Both are moving
in fluids and whether air or water, the physics is the same.

So there's a short and possibly refutable summary of why drafting on
a bike
can't directly be compared to drafting/riding in a boat.

I promise not to write about business if you stop making up physics. :-)

Mike
Mike,

OK, my analogies between bike and boat suck. And I'm just explaining
the physics badly. I deliberately left out rolling resistance and
laminar flow and all that stuff *bacause it isn't important to drafting
in a boat*.
Drafting works on a bike because if you are behind, you are riding in a
lower pressure area and that the effectiveness of this draft increases
fairly smoothly as you get closer. There is no *noticable* period to
the wave coming off a bike - just an increase in resistance which makes
you put out more effort.
This isn't the case in a canoe. Yes, hull speed is fairly arbitrary,
and yes, it's pretty easy - assuming you have the skills, power and boat
design - to surf a wave and exceed hull speed without extra effort from
the human motor - but that throws a new item in the equation - gravity.
You are paddling downhill, and use the effects of gravity to overcome
the bow wave and surf/plane. That's not what I'm talking about.
Drafting in a canoe or kayak is using the waves generated by your boat
and the boats around you. It is very, very different than riding a
bicycle. Most fla****er canoe/kayak racing takes place at, or near
'hull speed'. Not surfing, but at a point where the power to make the
boat go faster increases so rapidly that normal human beings cannot
sustain that effort. The only exception to this is when you get shallow
enough that you can plane a canoe of flat water by overcoming the bow
wave, and even then the amount of effort required to sustain that is
quite high, and difficult for even the best to maintain for more than a
few minutes.
Arbitrary, yep. Different for different boats, yep. And a big
difference from just playing with the physics of a single boat. Since I
don't have a copy of Marchaj's book, I can't compare the graphs you
cite, and I'm quite certain of their validity. But I doubt there is much
written in there about the effect of sitting 1/2 boat length off the
stern and just to leeward of the lead boat in a one design race. It
just isn't a place to be in a sailboat. Very different application, and
the position of the trail boat relative to the wave generated by the
lead boat is meaningless compared to the fact that the lead boat is
stealing the wind.

Marsh