Ed, that's the clearest and most succinct explanation I've seen yet - well done.
 
Designer's drawing  (or half model) ==> table of offfsets* ==> full-sized
lofting ==> wooden patterns of major parts ==> major parts built (for example:
keel, stem, transom, knees, breasthook) ==> boat
 
*the table of offsets is just a table with the boat's lines expressed as points
in space referenced to a base line.  Many times, the builder picked off the
points he wanted from the designer's drawing (or more likely, the half model)
and just skipped the table of offsets, going directly to the full-sized lofting.
 
Sails were lofted, too - since they're three-dimensional, not flat, objects. 
 
Story sticks were used to transfer the actual physical dimension found by
lofting the boat/ship between the three views on the lofting.
 
wr/Pete Leenhouts
 
   
 
In a message dated 7/19/2018 6:15:00 PM Pacific Standard Time, ruby1638@a...
writes:
 
Boy
 
I just took a stab at explaining boat lofting in simple terms and I failed.  The
Wiki entry is not very satisfying, and I like Phil’s start on it.
 
In short, it is a way to draw a 3 dimensional curved object in two dimensions
using 3 drawings that share points between them.  It is usually applied to
boats, and the full sized drawing were done on the loft floor - hence the name.
We still have a sail loft, where pieces of a sail are laid out for assembly on
the big, open floor.
 
http://www.douglasbrooksboatbuilding.com/lines.html
 
Look at the second drawing down - a simple small boat.  All three drawings are
on grids that are shared among them.  The top drawing from the end shows the
center to the back on the left, and the center to the front on the right.  Just
look at it for a minute and you can see how the drawings all share among them.
To actually exist in real life, a  point on one drawing has to also be a point
on the shared dimensions of the other drawings.
 
It can get complicated - the Kalmar Nyckel is a tall ship that I worked on
during construction.  It is 98 feet on deck and we couldn’t make a full sized
drawing, so we made one 49 feet long and folded on itself so the very front and
the very back were on top of each other.
 
 
Here is the bad attempt:
 
Anybody can conceive of a pretty looking boat, but how do you draw it so that it
can be built.  How do you make 2 dimensional drawings  that can be translated
into a shape that actually exists?
 
Lofting is most frequently associated with boats, and it is the accurate
(usually full-size) drawing that combines side view, end view and top view to
reconcile the shape into something that can be built.
 
Imagine this - I have 3 grids to draw on, all using a common starting point or
baseline.  If I draw the side of a boat, a point on its surface will have 2
reference points, length and height.  If I then draw it from the top, this
drawing will share the length, but add width.  If I then draw it from the front,
it will have width and height taken from the other 2 drawings.  If the point
does not share the 3 dimension on all 3 drawings, then you change some
dimensions and re-draw until it does.
 
A point on the surface of the boat will have to share its reference dimensions
on each of the three drawings.  Curved lines are drawn through a series of these
points,
 
In practice, the naval architect draws these 3 perspectives, and reconciles
dimension and shapes unitl it all works out. But his drawing might be only 2
feet long, so his dimensions, even if taken to 1/64 of an inch, will be within
almost 3/8” on a real 40 foot boat - no where near close enough to ensure that
shape will be buildable.  So once you have made the small 3 drawings full sized
you have to start erasing lines, changing dimensions on 2 or 3 of them, and re-
drawing curved lines to meet the new dimensions.  Once the lines are within
about 1/16 to 1/8” of being reconciled on a 40 foot or so boat, you are ready to
build.
 
Once you have the drawings all reconciled, you can then make patterns for pieces
right off the floor- and they “should” fit right in.
 
Sorry if I muddied the waters so to speak.
 
Ed Minch
 
 

On Jul 19, 2018, at 8:23 PM, Dragon List  wrote:
ok, i’ll bite.  what’s “lofting”, then?

bill