Question for prof. Tilley

I can explain what it is.  I can't explain just why it's drawn precisely that way; that seems to have been a matter of convention.

It's a scale.  The vertical lines in it are spaced one scale foot apart.  The vertical line at the extreme left is located at the "aft perpendicular," and the one at the extreme right marks the "forward perpendicular."  The numbers underneath represent the distances forward from the aft perpendicular.

There are seven horizontal lines, dividing the space between the top and bottom ones into six equal spaces.  The horizontal lines, so far as I know, are really only useful at the extreme left; they could just as well be omitted elsewhere on the scale, but rarely if ever are.  In the first, foot-long space at the left (stern), the draftsman has drawn an inverted V, with its apex located carefully in the middle of the space.  The points where the legs of the V intersect the horizontal lines mark intervals of an inch.  If, for instance, you want to measure a distance of three inches, put one point of your dividers at the intersection of the middle horizontal line and the left vertical line, and adjust your dividers till the other point hits the intersection of that same horizontal line with the left leg of the V.  That leg of the V hits the second line from the top at five inches, the third at four inches, etc.  (Describing it verbally takes at least ten times as long as doing it.) 

It's a rather clumsy system; it's obviously easier to use a ruler - and I rather suspect that's what the typical eighteenth-century person using one of these drawings did.  (Remember, though, that most Admiralty drawings were originally made on the scale of 1/4"=1', so the V was actually pretty big: 1/4" wide, to be specific.) 

Thank goodness they did it that way, though.  It's almost impossible for a modern publisher to reproduce such a drawing without including the scale bar.  I get explosively irritated whenever I encounter a drawing whose idiotic draftsman has indicated the scale of it simply by writing "Scale:  1/4" = 1' " on it.  It's just a matter of time before the drawing gets reproduced in a book, or elsewhere, at a reduced size.  (Book designers, who get their training in art schools and frequently have no comprehension whatever of how ship plans work, are notorious for pulling stunts like that.)  If the draftsman includes a scale bar, on the other hand, you can always figure out the scale.  (It's worth noting that Howard I. Chapelle, in most of his works, used the same, old-fashioned system the Admiralty draftsmen did.  Bravo.)

For the modern ship modeler using the plans, all this is of minimal practical relevance.  What's essential in working with old drawings like these is to get them reproduced - accurately - to a known scale (preferably that of the model you're building).  (Unfortunately that's often easier said then done.  Admiralty drafts, being drawn on linen and, in most cases, having been stored rolled up for prolonged periods, are notoriously prone to distortion.)  Once you've got a reproduction of the drawing to a known scale, you can use your modern measuring devices and forget the eighteenth-century scale bar.

Admiralty drawings are loaded with lines and other markings that aren't really relevant to most modelers.  Through most of the eighteenth century, for instance, the cross-sections of a warship (i.e., the shapes of the frames) were derived from the arcs of circles.  Modelers sometimes get baffled by mysterious lines on Admiralty drafts that, in fact, identify the locations of the centers of the circle arcs - which, unless you're building a plank-on-frame model and drawing the individual frames for yourself, don't make any difference to you.

The bottom line is that these things are a joy to study.  Anybody who's done any drafting at all has to be in awe of the typical Admiralty drawing - not only for the information in conveys, but for the superb artistic quality of it.  Traditional drafting is a dying art; the Admiralty drafts are among the finest examples of that art in existence.

Hope that helps.

jtilley wrote:

It's a rather clumsy system; it's obviously easier to use a ruler - and I rather suspect that's what the typical eighteenth-century person using one of these drawings did.

I was taught, ages ago, that the graphical scale was prefered over a ruler or scale as it was known that both the vellum upon which the plans were drawn, and any ruler used, were subject to dimensional changes with temperature, humidity, and/or age.  (Used to be ivory, then bone, were prefered materials to engrave as scales--but not inexpensively, then or now.)

So, if a person were wanting the distance from keel to main deck at the third station along the body profile, one set ones dividers to that distance.  Then, you laid the dividers along the scale to cipher the feet, and used the datum diagonal to render inches, and fractions, if a person were of a mind to, to scribe out the measurment.

Now, I'm wanting to remember that Chappelle goes to some lengths describing the construction of a good scale (where, I'm not remembering at all). I remember that he prefered the 'modern' method using two diagonals, as that let a person better glean fractional inches from a measurement.

I too, lament the number of otherwise intelligent people who have not yet learned that there are others who have little care for the precision of their drafting out there.  But, then again, I've taken to using the old-fashioned graphical scale, and running it in both "X" and "Y" axes--the better to 'protect' things if graphically "dragged" to fit, rather than use the "maintain proportions" option.

Well, that explains why the intervals of one foot are marked all along the length of the ship.  It doesn't explain why all seven horizontal lines run the full length.  (One line, with all the one-foot intervals ticked on it, would serve the same purpose.)  I guess one could draw one's own V in each "box," but that hardly seems like a logical reason for those lines to be there.  I'm inclined to think aesthetics had a lot to do with it.

Once in a while one sees a slight variation on the theme, wherein there's a single diagonal line running across each one-foot long "box."  That makes a bit more sense.

I don't know when vellum came into use for such purposes.  (The American Heritage Dictionary - my favorite - defines it first as "a fine parchment made from calfskin, lambskin, or kidskin and used for the pages and binding of books," then as "a heavy off-white fine-quality paper resembling this parchment."  I can't recall encountering any ship plans that meet the first definition; all the old Admiralty drafts I've seen are on drafting cloth (i.e., linen).  Modern drafting vellum, in my opinion, is excellent stuff; I personally prefer it to film for most of the stuff I get involved with.

Thank you for the most comprehensive anwer on this subject, professor. It may have taken ten times to explain in words, but it took me at least twenty times to read before understanding it completely, since I have to translate everything (in my mind), I can fluendly understand, speak, read and write "normal" english, but this is rather on the "technical" side

The reason I asked is that another project is slowly bubbling in my mind ; someone (or even more than one) here is (are) building HMS Surprise and that discussion has been pushing to do an Aubrey-ship myself (or at least trying to do, since my woodbuilding skills are still pretty basic), however, just another Suprise was not an option for me, I want to do the ship that started it all for our "captain" : HMS Sophie.

The above plan is the plan on which "Sophie" might have been inspired, since it beard the name that is mentioned by one of the officers in the first book : "Vincejo".

What I'm still a little puzzled about these admirality plans, is that there is no indication of what's on the deck, or is this information only ommited by the person who published these drawings on the internet ? 

Admiralty drawings vary somewhat in content - and, as Dan Cooper has implied, publishers don't always reproduce everything that's in the original set.

It would be hard to designate what consititutes a "typical" set of Admiralty drafts, but they often include a combined inboard and outboard profile (i.e., side view), a body plan (front and rear views), and one or more deck plans.  The amount of detail regarding deck furniture varies quite a bit; sometimes it's shown in quite a bit of detail, and sometimes omitted almost entirely.  Another source of confusion:  the originals were often drawn in several colors of ink, with, for instance, the internal features of the hull in red.  The colors have long since either faded or darkened, and in any case they don't show in black-and-white reproductions.

Sails and rigging are rarely included, because (a) that sort of thing wasn't the responsibility of the shipyards for whom the drafts were drawn, and (b) sails and rigging were generally pretty standardized.

It's not unusual for one or more sheets in a given set of Admiralty drafts to have disappeared over the centuries.  I have no idea whether the deck plans of the Vincejo are extant or not.  (The name, by the way, sure looks distinctly Spanish; I wonder if this is a captured vessel.  If so, the availability and detail of the Admiralty drafts is even more of a crap shoot.)

The only way to answer these questions definitively is to look up the ship in David Lyon's book, The Sailing Navy List.  That volume contains basic data on the National Maritime Museum's plans holdings for all British sailing warships.  (The NMM is the official repository of Admiralty drafts.)  Unfortunately the book is quite expensive and rather hard to find, but good libraries have copies - and other libraries, presumably, can get them via the Interlibrary Loan Service.

Sorry I can't be more helpful.

Don't worry, professor, you have been very helpfull on my little quest here

 

PS : one more (I promise it's the last at the moment) teenie weeny little question ; it's been about 3 years now that I've red the first book and someone mentioned something that I really can't remember about the Sophie.  Was she a snow-rigged ship ?  I know what a snow is (although can't say in english just by heart) but I just don't remember is if it was said so in the book. 

I don't know the answer to that one.  I have to confess that, though I've read several of the O'Brian books and have a great deal of respect for him, I don't really consider myself one of his biggest fans.  If I remember correctly, the Sophie only appears in the first book.  It shouldn't be too difficult to page through that volume and find most of the relevant references to the ship.  Or perhaps somebody who is a big O'Brian fan (there are several of them among this Forum's participants) can remember more than I can about the book.