: I'm at the point in my skin-on-frame West Greenland kayak were I'm lashing on
: the chine stringers, and I needed space in my shop to start cutting forms
: for a new boat, so I put the kayak on the floor. It seems to me that there
: is a lot of rocker in my kayak. How much rocker should I be looking for?
: Is there any good way to measure this so I could tell if I have too much.

: Thank you,

Bryan

I agree with West's 1.5" to 2.5" rocker average at the transition from the
keel to the stem / stern. I've seen greater rocker here also. However, it
also depends on the length of the end plates.

For a given LOA, if the ends are short and steep, then the point of
measurement will be farther forward on the keel(for the bow), generating
greater measured rocker. If long and shallow, then the point of measurement
will be further aft and indicating less rocker. There will also be a
difference between the stem/stern since the stern is generally shorter than
the stem causing the stern to appear to have more rocker.

To measure rocker, I place the boat on foam carriers at 3 feet from the stem /
stern . Then I measure from the stem /keel and stern/keel transitions to the
ground and also from the lowest point at the center of the keel to the ground.
The differences are rocker for the bow and stern. The above assumes that the
ground is level. In the example you will notice that at 3' the rocker (fore /
aft) is the same (1.5") but the bow / stern rocker differ due to different
measuring points.

If the kayak is flexible along it's length, it's more accurate to keep the
keel center off the ground during measurement as the the hull may sag towards
the stems if the keel is resting on the ground. This could give you a false
reading.

Paul mentioned that hull flex ( in the water) will contribute to more rocker.
I have not found this to be the case. The frame, though flexible, will
generally maintain it's measured rocker in the water. It would be of no value
to design and build in a given amount of rocker, only to have it altered once
in the water.

The greatest load in a SOF kayak is normally at or near it's balance point, but
that is also the point of greatest resistance from the water due to the boats
surface area at this same location. This resistance becomes less away from the
center, whereas the amount of load also decreases proportionately. It is this
offsetting resistance that maintains the designed rocker.

There are other factors, such as volume distribution along the hull, and
grossly over or under-loading, but generally a properly loaded SOF will
maintain it's designed rocker. (125 - 200+lbs for a typical Greenland
configuration)

My own boats, having smaller diameter stringers (aluminum) than a traditional
wood SOF, generally have more longitudinal flex. In addition, folders are
generally more flexible still due to the multiple sections in each stringer.
However, they maintain their designed rocker.

Perhaps the other folder builders on this forum would like to comment based on
their "rocker" experiences as they may differ from my own.

Sorry for being so long winded, but this is something that I'm constantly
playing around with.

Tom