Rising-line, how to determine?

I assume what you're talking about is the "rising line of the center of the floor sweeps."  The question is one I've wondered about myself quite a few times.  I don't have an answer.

Late-seventeenth and eighteenth-century British Admiralty draughts have quite a few lines in them that don't make much sense to modern eyes.  The basic reason is that the cross-sections of hulls in those days were drawn using a compass and ruler; the curves in the cross sections are made up of circle arcs, and the mysterious lines show the shipwright where to put the point of the compass and where to end the arcs.  With a little effort (and, usually, reference to a book to remind me how it works) I can usually figure out what all the lines in an Admiralty draught are; what we're doing, in effect, is looking backward at the design process to see how the original draftsman laid out the shapes on the drafting cloth when he designed the ship.

What baffles me, though, is that lots of Admiralty draughts are of ships that the Royal Navy acquired after they were built.  (Famous examples:  H.M.S. Bounty, the U.S.S. President, and the Continental frigate Hancock.)  The process of "taking off the lines" of an existing ship obviously involved taking measurements of the hull, decks, and fittings in dry dock - an enormous job, but theoretically straightforward.  But the Admiralty draught of the Hancock, for example, shows the centers of the circle arcs for drawing the cross-sections of the hull.  How on earth was somebody able to figure that out in an existing ship - and, for that matter, why did he bother?  (In that particular case, I suppose it's possible that the Royal Navy was particularly interested in the details of the ship's lines; the Hancock had the reputation of being unusually fast.  But why would anybody need to know the centers of the arcs in the cross-sections of the Bounty?

I once discussed this with the late Merritt Edson, long time editor of Nautical Research Journal and about as knowledgable a student of such things as I've ever encountered.  He couldn't figure out the answer either.

Maybe the answer lies in what one of my teachers called the IFF - International Fudge Factor.  I suppose it's possible that a draftsman who was thoroughly familiar with contemporary practice (which those guys obviously were) could look at an existing hull, take some measurements of it (he could locate the "height of greatest beam" lines, for instance, pretty accurately), and interpolate the other points on the basis of experience - with the assurance that nobody was likely to disagree with him.  That doesn't seem to have been the way these people operated, but it's the best explanation I can think of.

Anybody who's spent any time with those old drawings can only admire and revere the people who drew them.  Nowadays drafting is a dying art; CAD and other computer programs have turned designers of buildings and ships into computer operators.  In many ways, of course, that's a good thing.  But the men who drew those old Admiralty draughts, with their ruling pens, compasses, ivory rulers, and little else, were true artists.

John:

I have had quite a bit of experience reading and interpreting old line drawings over the past few years. Nothing like Edson had, but my fair share.

One thing to keep in mind is the plan drawing method you mentioned. The draftsman began with those circular arcs to form the sections in the body plan. He took the greatest breadth in a section and then used that measurement to calculate the arc of the compass sweeps he would use to form that body section. Once the sections were established, he would add the diagonals and plot them in the half breadth and then plot the rising line of the floor timbers (a proportion of the max breadth for each section) and the height of the point of greatest breadth at each section, both of which were plotted on the sheer profile drawing. These were all used in fairing the body sections to ensure that the sections would produce a smooth hull surface. The diagonals were useful in showing that the hull could be smoothly planked as the lines intersected the body plan lines at much more nearly right angles than the waterlines.

By the by, those waterlines were added after all the fairing was done. It was not until well into the 19th century that the waterlines were actually used to develop body sections. Back in the 18th century and before, the body sections were used as a basis for developing the waterlines.

Now, that is what they did when designing a ship from the start. If they captured a ship or bought a ship from which they wanted a lines drawing, then the process had to go in reverse. They measured the hull in drydock and then took those measurements and then went through the math to determine the appropriate compass sweeps to generate the curves of the body sections necessary to reflect the hull form as it was measured. Normally, the body section curves were all a portion of the section's max breadth, but if the original body sections that were used to generate the existing hull were drawn a different way, then the draftsman drawing the lines from that hull would have to go through the math and figure out, as closely as he could, the compass sweeps need to generate that body section curve. The problem here is that it would be very difficult to do this accurately, so in many cases where they took the lines off an existing hull, they had to make some sort of compromise somewhere in the drafting process, the result of which may be that the resulting plan does not necessarily reflect accurately the hull they measured. No doubt the differences are slight and perhaps in many cases not worth mentioning, but they are there all the same.

To answer the original questions. the rising line of the floor timbers was generated by plotting the heights of the ends of the floor timbers from the body sections. Those heights were measured up from the baseline to where the floor timbers came out from the centerline at a given body section. So, the end of the floor timber comes so far out from the center line of a given section (1/2 or 2/3 of the sections max breadth, divided by two) and then that marked is plotted on the body section. (this measurement will be used to help determine the arc of the sweep of the floor timber in the drafting process for the body sections)

Now measure up at that breadth from the base line to get the height of the point of the end of the floor timber for that section and transfer that mark onto the side view of the hull (sheer profile). Once you have that same mark plotted on every section and then transferred on to the sheer profile, you can lay a flexible batten on the sheer profile, connect all the dots and the you have the rising line of the floor timbers.

If I can help further, shoot me an email at rus3466@yahoo.com.

Russ

Wow, the amount of know how present in this forum keeps amazing me. I had to read the last post twice before it started to make sense…

Maybe I ought to explain why I started this particular thread. Beware…long story.

I have started work on the 1:180 Airfix HMS Prince 1670. This kit is almost certainly based on the magnificent navy board model in the Science Museum in Kensington. For those who don’t know how that model looks like:

http://www.old.modelarstwo.org.pl/szkutnicze/galeria/inni/prince/index.html

The Airfix kit is a nice one but not good enough for my taste. So I started to modify some things; opening windows, scratch building gratings and so on. While I was doing this I thought: “hmmm…funny how a few strips of styrene can make so much difference in appearance, it really adds to the overall look of the model and it is nice rewarding labor”.

While I was searching for more information about the ship I stumbled upon a German book I bought years ago; ‘Das historische Schiff als Modell’. In this book there is a nice dockyard model of HMS York by Willibald Meischl. This model has the same looks as the Prince only smaller.

A nice feature of these dockyard models is the fact that the decks are only partially planked so that the onlooker gets a view of the inner parts of the ship. “Could I do this with my Prince as well?” was my next thought.

And then it hit me. I’m going to convert my kit into a dockyard model like the one in the Science Museum!!!

So, what has to be done? Open up the gun ports, scratch build and partially plank all decks, sanding the hull below the lowest whales smooth, scribe all ribs on the hull and cut the space between them away (this is the part where the rising-line comes into the picture), build up the thickness of the ribs inside the hull, add deadwood, keelson and lengthen the masts until they rest on the keel etc etc etc.

Can it be done? I really think so. There are some problems off course like: where to get 72 guns with their carriages which are obviously not included in the kit? I’m sure there are some hurdles to take but when overcome…wow!!!

Please feel free to add your thoughts, objections and ideas, they are all very welcome.

Bryan:

I get what you are trying to do. Not to dampen your obvious enthusiasm, but it seems like an awful lot to go through with a kit. I wonder if you wouldn't be better off building the model from scratch.

But, if you are going to go through all this with a kit, here is an easy way to mark out the rising line. Take a pice of paper or thin carboard and cut a strip that will lay flat along the length of the hull. Place it so that it is a bit out from the keel in the midsection and then let it sweep up the hull towards the stern and towards the bow as well. Let it take a natural curve and only adjust it so that it will curve along the length of the naturally. Do not force it into any curve that it would not normally take on its own. Tape it down when you are satisfied with height of the line and its curvature and then draw in or scribe the hull along that line. This method is a guess at the rising line, but it is easy to do and the result will be pleasing, I think.

Now, if you want to take a really involved tack with this process, then use a metal contour gauge like they use in tile setting to reproduce the body sections from your hull. These gauges can be pressed against any shape and the little pins adjusted so that when you take the gauge away from the object, it has recorded that shape.

Put the gauge against the hull at a given point (start at the midsection) and mark where you are on the hull. Adjust the pins so that you reproduce the hull's contour at that point. You now have something like a body section from a ship's plan. Once the gauge has reproduced a given section, lay it down on a piece of paper and use a pencil to mark out the body section contour onto the paper. Just mark dots at intervals on the paper and then use a french curve or something similar to create the complete section.

Do one section in the middle of the hull and two or three more spaced evenly along the hull forward and aft. Mark on the hull where you record the contours so you will know later on. When you have those contours marked out on the paper, measure the greatest breadth on each of them, divide by two, and that will be your total breadth of floor timber for that section. You are only working with hull halves though, so you will only need half the total breadth of the floor. Measure up vertically from the keel on your section curve to the point where the floor timber half breadth measurement intersects with the curve of the section. When you have the half breadth of the floor timber for each section, measure up to that height from the keel of your preformed hull and mark it on the outside of your hull at each section where you took the contours.

Another way to do this is to measure along the curve of the hull section from the keel up using a paper tick strip to mark the total distance up the curve. Lay the paper along the curve, mark the keel and then mark where the floor timber is along the curve. Then lay that paper on the corresponding section of the preformed hull and line up the mark for the keel and then mark off where the floor timber is on the hull. This might be easier to do with the preformed hull.

With those heights marked on the hull, lay a flexible batten, say a piece of strip wood about 1/32" square, along the hull and tape it down so that it intersects each point you have marked on the hull. Now mark the line along the edge of that batten and that is your rising line.

Hope this helps.

Russ

Russ and I apparently were typing our second posts simultaneously.  His first one essentially elaborates on what I said in mine.  The full name of the rising line is "rising line of the center of the floor sweeps - i.e., it's a line on which all the center points for placing the compass to draw the floor sweeps lie.  (In practice, the Admiralty draftsmen usually located the rising line on their drawings a few feet above its actual location, to keep it from getting confused with the plethora of other lines near the bottom of the ship.  Everybody using the drawing was supposed to understand that.)  By dint of extensive measurements and interpolation (that's where the IFF presumably came into the picture) it would have been possible to guesstimate the location of the rising line fairly accurately on an already-existing hull.  I do wonder, though, if they had some method of doing it that's escaped modern students.  And I still wonder why they did it.  It seems like the rising line - and various other lines and points having to do with the centers of those circle arcs - wouldn't have any practical value after the ship was built.

Bryan - your project sounds fascinating - though I wonder if you may not end up spending just as much time and effort modifying that Airfix kit as you would working from scratch!  A couple of points are worth bearing in mind.  One - the conventions employed in the framing of the old Board Room models changed over time.  The spacing between the frames, the amount of planking included, and the layout of the joints in the frames all varied.  Generally speaking, as time went on the spacing got tighter and the amount of planking increased, until by the mid-eighteenth century the framing on the models was approaching a literal representation of the real ships' framing.  (There are a few old plank-on-frame models that DO literally represent actual framing practices to scale, but most don't.)  My suggestion would be to stick with the way it's done on the Science Museum model - but don't be surprised when you see photos of other models on which the frames are laid out quite a bit differently.  Two - nobody has ever, to my knowledge, figured out just how the guys who made those models determined how they were going to cut the frames to produce the characteristic gaps.  Some people have speculated that the rising line had something to do with it, but that hasn't been firmly established.  And the method, whatever it was, almost certainly changed over time.

The best, most detailed discussion of all this is in John Franklin's book, Navy Board Ship Models.  I highly recommend it to anybody contemplating such a project - if only to emphasize just how complicated the whole process is.

People have speculated extensively over the years on the question of why those old models were built, and why they were built in that manner - with exposed frames that, with the few aforementioned exceptions, most definitely do NOT demonstrate how the framing of the actual ship worked.  Two old stories are that the models showed the stupid politicians how the ships would look, and that the shipwrights used the components of the models to build the ships.  The latter is obviously impracticable nonsense, and the former is extremely unlikely.  My guess is that the models were built for exactly the two purposes they now serve:  to provide a three-dimensional record of the ships, and to serve as magnificent decorations.

Incidentally - there was one plastic H.M.S. Prince kit that predated the Airfix one.  It was sold in the U.S. by UPC; apparently it originated with some Japanese company.  It was a dreadful kit, owing most of its parts to a pirated version of the Revell Victory.  The most interesting feature of it was the painting on the box, which some Japanese artist apparently had painted with a photo of the Science Museum model as his one and only reference.  The painting showe the ship at anchor in a harbor, with blue water, blue sky, sunshine, flags flapping in the breeze - and unplanked hull frames sticking out of the water below the wales, with sky and water showing between them.

Good luck.

Gentlemen,

Thank you very much for your speedy and elaborate answers this far. They are really of great help.

I have thought of doing a complete scratch build project but that would mean scratch building everything from the keel up!!! Lack of decent plans to start from is also a problem. With this kit at least I have a solid base to work from.

But the one thing that is really holding me back are the decorations. I’m not a sculptor (I have tried though, not my thing). The carvings make or break the overall appearance of the model. I have seen too many beautifully constructed models (in a technical way) that were destroyed by the hideousness of the attached decorations (sorry, no offence intended towards anyone).

In my humble opinion one should only try to model these extensively decorated ships when one masters both crafts. That’s what makes model makers like, for example, Donald McNarry so unique.

I couldn't agree more, Bryan.  I've met a few people who contend that the quality of the decorations on a  ship model is irrelevant; that if the structural details are well done, the appearance of the figurehead, transom carvings, etc. doesn't really make any difference.  Those folks are, of course, fully entitled to their opinions.  Personally, I'm not a miniature wood carver; I don't have the training skills to do such work, and I don't think I ever will in this lifetime.  I've known a few modelers who are good at it; most of them have a solid, formal academic background in art.

What I have discovered, though, is that there are other ways to conquer that particular problem.  The "carvings" on my little model of the frigate Hancock are, with the exception of the figurehead, made from Milliput epoxy putty.  (The figurehead is a much-modified styrene HO railroad figure.)  The great virtue of Milliput is that it gives you more than one chance to get things right.  If you don't like your first attempt, you have about three hours to change it.  Some people claim I'm using a slightly illegitimate shortcut, but I don't think so.  I'm pretty sure Donald McNarry uses something similar for the "carvings" on his models.  (I'm not sure about that; he's written quite a few articles about his techniques, but I haven't seen one that really explains that particular aspect of his work.)  His first book, Shipbuilding In Miniature, describes how - at that early point in his career - he made his "carvings" from adhesive mixed with gilding powder.  I think he developed something more sophisticated later, when he started working in somewhat larger scales.  But his boardroom-style H.M.S. Prince on 1/600 scale (that's not a typo - 1/600) is hard to believe.

It does occur to me that people who do a lot of reading about ship models (including me) sometimes get particular notions into our heads of how models of ships from particular periods ought to look.  Maybe we'd be well advised to be a little more flexible in our thinking.  Nobody thinks a model of the U.S.S. Constitution with its hull planked all the way to the keel looks the least bit strange.  So why should we think there's something "deficient" about a model of the Prince built in that same style?

In that respect, perhaps we're erring in the opposite direction from some of our predecessors.  I know of at least one beautiful eighteenth-century Board Room-style model in a major museum whose bottom got planked up in the twentieth century because some curator said "real ships don't have unplanked bottoms."  And at the Mariners' Museum, where I used to work, one of my predecessors "improved" a superb model of a 1930s-vintage Japanese freighter by taking all the fittings off and painting them with black lacquer - because, as he put it rather scornfully, "you don't see ships steaming around with gold ventilators."  (Gold was the word for them, all right.  All the metal fittings on the model were originally gold-plated.  I made a half-hearted effort to undo the damage, but the guy had made so many other devestating changes to the model, and I had so little time in my schedule to work on it, that I gave up.) 

Bottom line: one of the great things about the hobby is the scope it offers for personal approaches and taste.  If five skilled modelers build models of the same ship, all five probably will look significantly different from each other - and all five may well be equally accurate.  That's one big reason why, after fifty years, I'm still at it.