: I was laying out my kayaks last night using the method described in
: Cunningham’s book. After I had finished taking the measurements I checked
: them against the anthropometrics. I found that the backrest deck beam was
: 2 1/2" farther aft on mine and almost 3 1/2" aft on my wife’s.
: Is this a problem? Did I do something wrong?

Not necessarily in either case.

Did you use the "balance beam" method in your initial calculations? If so, I'd stick with them. In my own case, there wasn't much difference between the two methods, but that will depend on your build. If you have to err in one direction or the other, putting your weight farther back is less likely to cause a problem. If your weight is too far forward, the boat will weathercock badly. I doubt that you'll end up with a boat that leecocks using your calculated measurements.