Re: [Paddlewise] Why does rocker and carving work?

> I'm trying to understand why rocker makes a boat turn
> easier.


How about this... sea kayaks carve turns for the exact opposite reason that
skis carve turns.  A ski has sidecut and camber.  I submit that a sea kayak
has reverse sidecut and reverse camber (aka rocker).  This causes the sea
kayak to have the reverse turn of a ski when edged.

Physically, here's what I think is happening....

Upon edging the kayak, water pressure builds up on the bow, pressing against
the lower edge. This causes a turning momentum away from the edge that is
dropped-down into the water.

At this point, the stern keel/skeg/rudder resists the turn that is initiated
above.  However, if there is little resistance, then the turn will build
momentum. If you have ever tried to paddle a whitewater kayak in a straight
line, you know what this feels like. Whitewater boats have NO resistance to
turning in the rear (eg. skeg/rudder/keel-like object).  Some sea kayaks are
similar... e.g. the P&H Cappella and the CD Gulfstream both have rounded
sterns and a skeg. With the skeg retracted, edged turns happen very fast.
With the skeg, edged turns don't happen without a lot coaxing. Incidently,
weathercocking is also very bad with skeg up, and nonexistant with it down.

Now, if your kayak has just enough keel so that the boat tracks well and
doesn't weathercock when held flat, AND if that keel virtually disappears
when the boat is edged, well then you have a boat that initiates and carves
turns all by itself.  You probably also have a Mariner kayak, since so few
other designs behave thusly... AND you definitely have a kayak which
absolutely does not need a prone-to-break-or-jam, cut-you-up-in-the-surf,
spongy-foot-bracing, destroy-the-beautiful-lines, mechanical-contraption
called a RUDDER!  ;-)

;-)

Kevin Whilden

***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************