Re: [Paddlewise] She needed a rudder

Scott wrote:
>Why do all of the fastest boats
>have rudders if simply edging the boat is so efficient?
>
Because when you design a kayak that sacrifices handling and just about
everything else on the alter of "Top Speed" an efficient rudder is a
necessary evil to deodorize that kayaks other handling characteristics.

Kevin wrote:
>>>>>>I have heard
that rudders can add up to 20% drag, but that is only hearsay. Perhaps
Matt Broze has some definite numbers. However I have definitely noticed
drag from rudders in boats I have tested, and also on skegs for that
matter. I still think that if the boat is balanced and well behaved, then
an expert paddler would not gain much benefit from the rudder, and this
might even be offset by the drag.<<<<<<

In 1986 Sea Kayaker magazine tested some kayaks in a ship model towing tank
at the U of BC.  They dropped the rudder (high aspect ratio, flat blade,
about 1/8" thick, free to drag straight back) for one of the three 3 knot
tests they ran and found it added 10% to the drag of the same kayak without
the rudder in the water. They thought there must be something wrong with
this test because that was way more drag than they were expecting
(considering the relatively small amount of extra wetted surface due to the
immersed rudder) so they repeated the test. They got the same results. I
suspect a well designed shaped rudder could cut that 10% extra drag in half.

James wrote:
<SNIP>>>>>In a 500 or 1000 meter race [this was thirty years
ago and more, I think the distances for races may have changed] the wind or
the wakes for other boats [if one was unfortunate enough to be not in the
lead] would require course corrections.  A 10,000 meter race is over an oval
course, with wake riding a crucial skill.  Absolutely impossible to ride
wakes without a rudder, let alone make a smooth turn.
The rudder does slow the boat, but it is a necessary evil.  I once had the
rudder fall off my sprint boat and I was amazed at two things: 1) how hard
it was to get where I wanted go and 2) how much the lack of rudder made the
boat more tippy.<<<<<<<<<

Same race lengths as now I believe. Apparently I do the impossible all the
time then (but not in a kayak design compromising everything else to top
speed). Wake riding was my ace in the hole when I was sea kayak racing and I
never used a rudder. In the 500 and 1000 meter Olympic sprint races the
kayaks must stay in their own lanes. Because of this the kayaks on each side
of the leader have a big advantage over the others as they can ride the
leaders divergent bow wake ahead of when all the other competitors can ride
it. Because they can't get directly behind the leader they are left with
their poor handling (rudder dependant) hulls attempting to ride what is
essentially a quartering/following sea (the most difficult course to
maintain in a watercraft). In that situation the losses due to the rudder
are more than made up for by the boost they get from gravity in riding this
wake downhill even though the angled (divergent) wake is also tending to
broach them and the rudder angle needed to correct the broaching is adding
even more drag than usual.
A sprint kayak is also a strong weather helming kayak (same "Top Speed" is
everything problem) and especially since they don't lean to turn well
either, they also need a rudder to compensate for weather helm in even a
slight side wind. If the wind is too strong the race gets postponed or
cancelled as well so these Olympic FLATWATER kayaks don't really need to be
seakindly at all, just fast.

My rudderless turns seem smooth to me (at least in a sea kayak) but I'm not
quite sure what James means by "smooth" in this context.

Yes, I think we could all learn a lot once the rudder breaks. Once it broke,
James discovered how dependent he had become on the rudder for both tracking
and stability (at least in the speed optimized sprint kayak he was using in
his example). How many of the rudder devotees of this group (who have been
paddling for more than a few years using a rudder) can say that they have
never had part of a rudder system fail to function for them? For those few
how many can say they have never seen a rudder system of someone else's
kayak fail. It seems a shame to me to become so dependent on such an
unreliable lover.

The sprint boat designers are going to try to remove some of the drag that
would be due to extra keel surfaces if they are going to have to put up with
the extra drag due to the rudder anyhow and the rudder can help with the
tracking. They can cut the wetted surface a bit that way and then depend on
the rudder for control to make up for some of the tracking loss from cutting
back the stern keel (to reduce its wetted surface).

A nearly round hull (like on a sprint kayak) doesn't change its shape much
when leaned so "lean to turn" control is minimal with them. Race kayaks will
not have sliding rudder pedals though, because solid foot braces contacting
the ball of the foot are essential to get the most leg power into the
stroke. Sprint kayaks usually have a solid foot bar with a central "tiller"
coming through the bar (that is "toed" side to side for controlling the
rudder).

Alex wrote (referring to gas pedal type rudder foot controls one poster
described as "newer"):
>>>>>>>NEWER!!!!!!!! newer, they've been around as long or longer than the
sliding
ones.
Well they have in the southern hemisphere.<<<<<<

Washington's Eddyline, for one, used gas pedal style footpedals on their
early Orca model (that dates back to 1977). Eddyline's WT500 model goes back
to 1975 but I don't remember how its rudder pedals worked.
Although they can be far more effective at transferring power than sliding
rudder pedals, unless the gas pedal style also allows for a solid perch for
the ball of the foot the gas pedal style footpedals will also take the calf
muscles out of play for providing much power (but they will not remove the
quads as a power source as well--as sliding pedals tend to do).

To expand on what Robert pointed out in his post, you can't strap a long
stick onto an inner tube and expect to get the hull speed of the long
stick's length. What you get is the hull speed of the inner tube plus the
added wetted surface friction of the stick. For the same reason the kayaks
with the finest bows and sterns are not the fastest ones even though they
look like they should be.

I'm trying to think of a simple way to test the relative efficiencies of
turning a kayak with a rudder vs. using a lean. Maybe we could test the same
kayak with the rudder up and leaned vs. having the rudder down and not
leaned and also vs. the rudder down and the kayak also leaned. On a windless
day we push the kayak to top (hull) speed (for consistency without a
speedometer) just before reaching the starting line. From the starting point
on we make no strokes but only coast to see which system will turn the kayak
the furthest (and maybe let the kayak coast the furthest as well). The
kayaks can be leaned prior to the last few strokes but must cross the
starting line while still perpendicular to it. I'm putting my money on the
rudderless lean followed next by the both rudder lean (at least with kayaks
that respond readily to a lean--not Olympic sprint boats or those kayaks
that track like they are on rails). On perfectly calm days I used to make up
to 180 degree turns this way in some kayaks (but haven't tried this yet with
a rudder).

Matt Broze
http://www.marinerkayaks.com


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