Re: [Paddlewise] skeg ups

The drop down skeg VS rudder discussion provides a pleasant change form the
usual rudder  VS no rudder debate and gives me the opportunity to serve up
some more pedantry. :-)

First, drop down skegs and rudders "do" the same thing, I.E. they alter the
turning moments about the Center of Gravity. Both can provide lift due to an
angle of attack with the water flow. You can get a more complete discussion
of these turning moments at http://home.ican.net/~735769/control.htm

Often we tend to think of directional stability in terms of the center of
lateral area and, while valid for hulls and control surfaces that generate
little or no lift it doesn't really apply well to lifting surfaces.
Sailboat designers learned that early on when they shifted from long keels
to high lift keels and their "rule of thumb" methods for finding the center
of lateral resistance no longer worked so well.

Rudders increase the effect by allowing an even greater angle of attack and,
if the rudder has a suitable section shape, it can provide significant
increases in lift. The two differ in degree of effect and in the ability of
one to allow a wider range of effect over the other. The skeg varies the
turning moments through adjusting the exposed area and the rudder (most
often) adjusts it by altering the angle of attack. In  anticipation of some
one raising the resistance issue, it seems that rudders more resistance per
unit area due to surface piercing effects or, in the case of under hull
rudders, due to cross over effects between the hull and rudder but that does
not mean that the net effort to paddle the boat increases. As I have pointed
out before, if the designer plans on using a rudder or skeg he can design
the boat with significantly less surface area that, when coupled with any
reductions in leeway and reductions in resistance due to heel should offset
the added resistance of the rudder. Unfortunately most people look at
rudders and skegs as "additive"  only as in "If we add a rudder to XYZ boat
it will have more resistance" rather than "if we design boat ABC for a
rudder or a skeg it will have less".

Individually one has to decide whether one sees operating a rudder with the
feet over a skeg with the hands as an advantage. One can easily set up the
skeg to operate with the feet so I don't see any inherent advantage in one
over the other in operation. I personally have no problem with deck mounted
controls but that has to do with my style of paddling. I kind of enjoy
steering with the paddle and heel but then I come from a canoe background.


An interesting aspect of skegs comes from their location. Both skegs and
rudders generate lift to offset leeway. A skeg mounted well forward would
work in much the same way as a centerboard on a sail boat producing a net
increase in efficiency when paddling in conditions that produce leeway. A
rather neat aspect deriving (possibly)  from a more amidships location comes
in the form of both reducing leeway and weathercocking that, depending upon
the shape of the hull, may not inhibit maneuverability.

Alex makes a good point when he blames builders for mushy foot pegs. I would
place the blame for include almost every ill attributed to rudders (Ditto
for skegs) squarely on the backs of builders.

Floppy, flat plate rudders with improperly swaged fittings and nylon straps
for length adjustment etc. will make a person weep. Many of the ills
ascribed to rudders have nothing to do with rudders and a lot to do with
builders. I have seen swages crimped with pliers, no thimbles, wires bearing
on the threads of bolts, stretchy nylon adjustment straps,   foot pegs that
slide right of the tracks, Etc. Etc. If we had built sailboats that way we
would have lots more room at marinas and overcrowding in cemeteries.











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