Ted,
I came into this 'discussion' a bit late, so bear with me.

I have read all the correspondence to date - 08-20-2006 - and I'm a little
confused.
Your initial Q was . . .' If I added 2 feet to an 11 foot sailboat with a
5 foot beam, what else would have to be changed in addition to adding an
extra frame. . . .'. There then followed a lot of back-and-forth, and
finally a reference & drawing. BOTH refer to a 13 FOOT BOAT !! ??

Anyhow . . . based on the initial Q, you wish to extend the LOA by 18
percent. That is really on the cusp of a 're-design', but within margins.
The Drawings give you some good, and basic, data points to do a 'take-off'.
They also give you 'station lines'. A 'legitimate' process would be to take
that 24 inches, divide it by the number of stations, then ADD that dimension
to the separation BETWEEN the present lines. THEN . . . LOFT the plan and
'check & correct' for fairness with a batten. Use a 20ft x 4ft piece of
white 'butchers paper' or similar. If it were me, I'd get a couple of 4x8
sheets of 1/8in Hardboard, butt them together, tack in place, and roll on a
couple of coats of water-based white primer. This is what I do to make parts
templates.

There are a number of books on lofting & building. Many illustrate how to
use the information you already have. I just read through one by Chappelle
which seemed to be 'contemporary' with this drawing. Also, take a look at a
re-print of a book by Edwin Monk - 'How to Build Wooden Boats' - from the
'30's.

Regards & Good Luck,
Ron Magen
Backyard Boatshop