>Terry Laughlin states that an advantage to "reaching out" and keeping the
>arm extended as long as possible is that it increases one's effective
>In sailing or in any racing of a boat which displaces (rather than rides
>over) water, there is a bow wave and a stern wave. As the velocity
>increases, the boat is effectively pressed down into the trough between
>these two waves. The longer the boat, the faster the maximum hull speed.
>Everything being equal, a longer boat will always beat a shorter boat,
>because of this.
>Now, I don't really see how this applies to swimming, at all. Even when
>the master himself (Terry) does this, the lead arm is way below the
>waterline. Unless the lead arm is literally half above and half under the
>water, the waterline length is not increased by this. So I doubt that a
>swimmer's "hull speed" is increased by the extended arm.
>I am not disputing that the extended arm helps. Terry correctly observes
>that the fastest swimmers tend to do this, so it obviously does something
>positive to improve speed.
>Question: Any other explanations of why the extended arm and forearm
>should help a swimmer go faster (compared to, for example, driving the
>hand, forearm, and arm through the same "hole" in the water at a 45 degree
>angle, until one attains the high elbow position?
I am not familiar with the intricacies of boat design, however, I do have a
degree in Aerospace engineering and work as an aerodynamicist. I maybe able
to help clarify things.
Your concern about the waterline is incorrect. I believe that the waterline
defines the amount of boat volume and surface area being influenced by the
water. It is true that the waterline and near surface region, due to the
proximity of a lower viscosity fluid (air), is more turbulent, and thus
will impart greater drag on the swimmer or boat. Regardless, I don't
believe that this is part of the theory.
I believe that when they say, 'everything being equal', they are referring
to total displacement and wetted surface area. Just because one boat is
longer that the other, doesn't necessarily mean it's drag is less. To fit
the theory and be valid for comparison, displacement and surface area must
be equal. This isn't true for a swimmer, however it doesn't make the
analogy useless. Ignoring the dynamic changes to displacement (or volume
of a swimmer in the water, due to waves, etc.) a swimmers displacement
can be assumed to be constant. This is can be assumed true since the body
will rise slightly out of the water as the arms enter, so that buoyancy
equals weight. What isn't constant is the amount of surface area, as the
arms enter and leave the water, the amount of surface area in contact with
the water changes. However, I don't believe that this is really significant,
either. I don't have a feel for the amount of friction drag from a swimmers
body, but pressure drag must be the more significant contributor.
Having said all of that, I believe that there is another aspect to the theory
that is more important and may help to explain the longer boat-less drag
concept. An important concept in determining the drag of an object is the
maximum cross-sectional area and the its distribution. I believe that this
is the crux of the theory that Terry is referring to. Basically, the larger
and blunter the object, the greater the drag. To reduce drag (but keep the
same displacement and surface area) you can stretch, or elongate, the object.
For example, take two identical cubes, grab one of the cubes by any two
opposite corners and pull on it until you begin to approximate the shape of
a pencil. If you now push both objects through the water, which one would
be easier to push. Terry may say, see I told you, a longer boat has less
drag, and he would be correct. But from an aerodynamic point of view, I
would say that it was the smaller maximum cross-sectional area and it's
smoother distribution. The distribution, of course, is the cross-sectional
area transition from zero cross-sectional area (just upstream of the object)
to the max (on me it's my abdomen) to zero again (just downstream of the
To sum up what could easily turn into a masters thesis, while the arm is in
the water and positioned out in front of the swimmers head, it is creating a
smoother transition of cross-sectional areas. In other words, the flow
about a swimmers body is gradually and relatively smoothly being moved out
of the way when the arm is in this position. As opposed to the head and
shoulders having to perform this operation alone. This will seem obvious
if you compare the push off from the side of the pool with your body in a
streamlined position and with your arms at your sides. The arms breakup
the flow gradually if they are out in front compared to your blunt head
and shoulders alone. If you try this, you can actually feel a tremendous
increase in the pressure drag and subsequent loss of speed. BTW, swimmers
legs automatically do this for the aft portion, unless the swimmer bends
the knees excessively or doesn't point the toes.
So, with this in mind, remember to roll your body so that you may stretch
out your arm as far as possible, making your body as long and as smooth
as possible. But also shielding you head and shoulders from taking the
oncoming flow of the water.
I'm not sure if I have cleared things up or confused matters worse, so
if you have any questions or comments, I would be glad to here them.
Good Luck, Larry John