RE: [Paddlewise] Comparing sweeps chine and round hull - 'inertial' vs 'damped' responses

From: MATT MARINER BROZE <marinerkayaks_at_msn.com>
Date: Thu, 10 Jun 2010 22:20:48 -0700
PeterO asked:

>>>>Something I'm still struggling to understand is why the Pittarak turns
more
easily upwind with a reverse sweep and more easily downwind with a forward
sweep. The centre of rotation (if that's the right term) must be quite
different between the forward and reverse sweep. <<<<<<



And when I asked, Peter clarified the way he leans for me:

>>>>>>....I can say for sure is that I lean forward and edge away from the
turn when using a sweep and edge into the turn when using a reverse sweep. I
think I lean towards the stern for a reverse sweep  and that the effect is
similar whether turning on the spot or moving forward, usually I'm turning on
the spot when going upwind, but its worth checking again....<<<<<<<





I'll bet, like most folks, when turning into the wind you are more comfortable
leaning/bracing more into the wind doing a reverse sweep than leaning downwind
to the outside doing a forward sweep/high brace. As I said earlier, the more
you lean the kayak the quicker it will turn. I suspect turning into the wind
you are willing to lean further to the inside (and into the wind) while low
bracing on a reverse sweep than you are willing do to the outside (leaning
downwind) doing a forward stroke. Turning downwind you are in the opposite
situation where you get to lean into the wind with the outside lean and must
lean downwind doing a reverse sweep. Since you naturally lean into a wind some
to compensate for the wind strength (to maintain balance) you aren't so far
off balance when leaning into the wind than when leaning at an equal angle
downwind.



With forward speed an outside lean with a forward stroke is most effective in
turning a wider kayak (and most kayaks) into a wind because maintaining speed
means you are being helped by the weathercocking tendency and for an equal
lean angle the stern keel will shed water better when the kayak is tilted to
the outside. You also gain the advantage of the side "lift" I talked about
earlier helping drive the turn.



Everybody should practice fast outside lean turns while maintaining good
bracing. The reason is that when the wind is strong you might still be able to
turn into it if you are willing to tilt the kayak away from the wind but might
not be able turn into the wind at all if you are afraid to tilt the kayak that
way. Practice this in strong winds when in a safe place. Being able to turn
into a stronger wind can be a real safety advantage. At speed, most sea kayaks
can turn nearly twice as fast with a good outside lean as they can with the
kayak level. I'm not making this up. When testing kayaks I time turns both
leaned and kept level, I do this comparison both when moving forward at
cruising speed and when spinning the kayak in place (in place the difference
is not as great but you can't normally turn a kayak into a strong wind as
easily in place as you can when getting some speed up accross the wind first
and just using forward sweep strokes). I have collected this data from most of
the 1000+ kayaks I tested on some spreadsheets (that include dimension data on
some 4000 one-person kayaks I know about--not including WW kayaks, surf skis,
wave skis, or downriver and flatwater racing kayaks).



In a strong wind with steep wind waves what happens is you make a turn into
the wind in the trough and then lose ground (water? angle?) when the bow rises
over the crest and is caught by the wind. The more angle you can gain in the
trough the more you can lose at the crest and stillhave made some progress by
the next trough. Turning speed is an important variable in this situation. The
length of the bow from the paddler (lever arm) and the windage at the bow are
some other variables that matter then as well. Weight in the bow (or the whole
kayak) is a big help and the weight and strength of the paddler are also big
helps when the wind is strong.
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Received on Thu Jun 10 2010 - 22:20:56 PDT

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