Re: [Paddlewise] Weatherhelming versus Weathercocking Usage

On 9/24/06, Dave Kruger <kdruger_at_pacifier.com> wrote:
>
> I got bollixed up and misused "weather helming" to refer to a boat which
> was lee cocking.  I did not realize weather helm was an exact substitute for
> weathercock.
>
> Does anybody have a link to an authoritative etymology of these terms?


Other replies have given a pretty good list of sources for the etymology but
I'm not sure they explained exactly what "weather helm" is.

First the term: "Weather helm" is the term used when the sailboat's tendency
to turn into the wind has to be countered by holding the tiller towards the
side of the boat the wind is blowing against (the "weather" side).

But, you may well be asking, why does it want to turn into the wind? It's
the combination of wind pushing against the sails and the resistance of the
keel against the water. Take a simple example of a sloop with one mast
having a "main sail" mounted on the aft of the mast and a "jib sail"
forward).  If you look at a side view of a sloop you will notice that the
mast is stepped forward of the center of the boat (often waaay forward).
With no sails up a sloop will tend to "fall off" the wind (turn downwind or
"leecock") because the wind blowing against the side of the boat will be
pushing against mostly the mast. The combination of wind thrust forward and
keel resistance aft will rotate the boat downwind.

If the sloop has only the main up then the wind thrust aft will overcome the
keel resistance aft and the sailboat will rotate into the wind. Most sloops
have their greatest weather helm if only the main is up. But even with the
main and the jib most sailboats will still exhibit some weather helm because
it's safest; if the helmsman falls overboard the boat will turn into the
wind and stop.

There are technical names for these forces, you may not be surprised to
learn:

The sum of all the wind forces acting on all the parts of the boat that are
above the water is a point known as the "center of effort".

The sum of all the water forces acting on all the parts of the hull that are
below the water is known as the "center of lateral resistance".

On any boat, any time the center of effort is aft of the center of lateral
resistance that boat, left to its own devices, will rotate into the wind
(weathercock) and any time it's forward of the center of lateral resistance
the boat will rotate downwind (leecock).

This all works exactly the same on a kayak too. Just imagine that it's your
body poking up into the wind that's acting as a sail (and for some of us
there is more sail than for others of us). If your body is forward of the
center of lateral resistance then the kayak will tend rotate downwind
(leecock). If you don't want it to do this you can either move the center of
effort aft or move the center of lateral resistance forward.

Take a look at your kayak from the side. Chances are that the cockpit is
slightly aft of the middle of the boat. In this case your kayak will almost
certainly have a tendency to weathercock or turn into the wind. If moving
your seating position to maximum doesn't change the way your kayak handles
in wind then you have to make some adjustments.

This is why a small adjustable skeg changes the way your kayak reacts in the
wind so effectively; it moves the center of lateral resistance. Remember
that when the center of effort (um... that would be you, mostly) is aft of
the center of lateral resistance (the sum of all the underwater resistance
forces acting on your kayak's hull) your boat will weathercock. Moving that
center of lateral resistance aft will tend to neutralize that and an
adjustable skeg can be used to create exactly the right balance between wind
and water so you go more-or-less straight.

What if you don't have an adjustable skeg? Well, if your kayak is
weathercocking so much that you find it difficult to control, you could add
some windage forward or subtract some windage aft. A great huge pile of gear
in one spot or another is bound to do it. <grin> But there are easier ways.

You could simply deploy - but not necessarily use - your rudder. As soon as
you deploy your rudder you have added an effective keel and subtracted an
effective sail; both way aft on your boat. This moves the center of effort
forward and the center of lateral resistance aft. So if your kayak is
uncontrollably turning into the wind merely putting the rudder into the
water should help. But, because the rudder is so far aft (and because it's
difficult to just deploy the rudder a little bit), it's possible that you
could turn a kayak that weathercocks into one that leecocks.

The rudder also can add a turning moment to the equation but this is only
effective when the hull is moving forward or backwards through the water.
And it works by adding resistance to that movement and "pushing" the stern
to one side or the other and thereby making the bow point at something else.
You can overcome a great deal of your boat's natural tendency to leecock or
weathercock by using a rudder but it will always add at least some drag; the
more the rudder has to overcome the greater the drag.

What if you have neither a rudder nor a skeg? Well there are still ways to
change the balance of your kayak but most of the easy ones aren't available
to you. You'll have to have some understanding of your kayak and how to
change its balance (that is, the balance between center of effort and center
of lateral resistance... not the tippy sort of balance).

During the last spate of weathercocking posts several people mentioned that
if they load their kayaks differently they can alter its behavior in wind.
This is because they are changing both the center of effort (windage) and
the center of lateral resistance. If the bow of your kayak sticks waaaay up
in the wind that adds windage forward (moves the center of effort forward)
and makes the boat more likely to leecock. Adding gear in the foward
compartment sinks the bow deeper in the water and reduces windage (moves the
center of effort aft) while adding to the effective keel area (moving the
center of lateral resistance forward). Likewise, adding weight aft sinks the
stern of the boat reducing windage and moving the center of effort forward
while simultaneously moving the center of lateral resistance aft.

The same things happen when you move your seat forward and backwards; the
balance between center of effort and center of resistance changes.

So if you have no skeg or rudder you will need to evaluate the weather and
sea conditions for your trip. Of course, we should all do this anyway and
most of us who paddle regularly understand pretty well what conditions cause
our kayaks to become difficult to handle. But those without access to quick
changes in their boat's balance need to be more closely aware of these
conditions.

So Dave... you asked what time it was and I more-or-less told you how to
build a watch. Hope it helped.  :)


Craig Jungers
Royal City, WA
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