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Re: S&G: Increasing rocker
By:Dave Houser
Date: 11/14/2007, 2:31 am
In Response To: S&G: Increasing rocker (Kudzu)

: Looking at building a B&B Diva Kayak. Reportedly it has very good tracking as
: designed. I would use the boat a lot in smaller creeks and harbors where
: maneuverability is more important that tracking. It will also be used on a
: large lake which can have big waves and wind where tracking is more
: important.

: I am thinking I would rather have a looser boat and just add a retractable
: skeg. Then when I need it I could simply lower the skeg when I need more
: tracking. I just don't care for a rudder. Of course I can't help but
: wonder if I am missing something. If this is a bad idea and I am not
: seeing it.

: The designer will work with me to change the design of the boat to increase
: the rocker and loosen up the boat. I would take care of the skeg design.
: Just looking for some input here.

I have found the most exhausting kayak to paddle is one in a crosswind that weathercocks that you have to edge and sweep with every stroke to stay on course. Changing any one or more of the following in designing a kayak will reduce or eliminate weathercocking. 1- Reduce keel depth at the bow (more forward rocker). 2- More keel depth at the stern (less aft rocker or a skeg). 3- More bow height (to catch more wind). 4- Less stern height (to lessen the sideways push of the wind on the stern). So adding rocker needs to be balanced (not necessarily equal) both fore and aft to avoid weathercocking or leecocking. Adding rocker does increase maneuverability but it also makes the bow plow more through the water slowing the kayak. By the way, moving weight back in a kayak does all of the above 4 so it reduces weathercocking.

Increasing tracking means making a kayak less influenced by crosswind and/or lateral waves. In reality it is just another way of saying making the kayak harder to turn by external influences (including you with your paddle). It is possible to have a kayak that is (cross)wind and(lateral) wave neutral, which means on the average it tends to go straight. And a wind/wave neutral kayak can be either hard or loose tracking. So all this means adding rocker changes more than just tracking and a design needs to be balanced.

So let’s talk about a deployable skeg. To be effective it must be on a kayak that weathercocks. So skeg up the kayak turns into the seas (wind). Skeg down the kayak leecocks to tack down wind. And with a partially deployed skeg the kayak is wind neutral to handle crosswinds.

So, if you increased forward rocker to increase maneuverability and added a skeg both would decrease weathercocking and if the original design was even close to being wind neutral you would likely have a new kayak design that would leecock, a real bummer.

I like a wind neutral kayak with no moving parts (skeg or rudder). I force this to happen with any kayak I build by test paddling the kayak in a crosswind before installing the cockpit coaming and final cut out. I move the seat back (and paddler) to the location that eliminates weathercocking (or forward to eliminate leecocking).

Messages In This Thread

S&G: Increasing rocker
Kudzu -- 11/12/2007, 10:24 pm
Re: S&G: Increasing rocker
Dave Houser -- 11/14/2007, 2:31 am
Re: S&G: Increasing rocker
Bryan Hansel -- 11/14/2007, 11:05 am
Re: S&G: Increasing rocker
Dave Houser -- 11/15/2007, 4:41 pm
Re: S&G: Increasing rocker
Bryan Hansel -- 11/15/2007, 6:11 pm
Re: S&G: Increasing rocker
Kris Buttermore -- 11/13/2007, 11:35 am
Adjustable Skeg Flash video *LINK*
Dan Caouette (CSFW) -- 11/13/2007, 1:49 pm
Re: Adjustable Skeg Flash video
Kudzu -- 11/13/2007, 4:53 pm
S&G: Increasing rocker
Jay Babina -- 11/13/2007, 8:58 am
Re: S&G: Increasing rocker
Paul G. Jacobson -- 11/13/2007, 12:15 am
Re: S&G: Increasing rocker
HenkA -- 11/13/2007, 1:01 am
Re: S&G: Increasing rocker *LINK*
Bryan Hansel -- 11/13/2007, 11:44 am
Re: S&G: Increasing rocker
Bryan Hansel -- 11/13/2007, 12:49 pm
Re: S&G: Increasing rocker
Kudzu -- 11/14/2007, 12:22 pm
Re: S&G: Increasing rocker
Kudzu -- 11/13/2007, 8:02 am