Bob Cleek

Hiya David,
 
I think part of your confusion is that your Yacht Endeavour is certainly not bluff bowed. Capt Cooke’s Endeavour has a typical blunt bow which is amongst the hardest of hull types to plank well. Many build logs showing planking are on this site,

Nor the famed Danish spidsgatter racers with their uncommonly high and large rigs and carry no backstays at all !
 

Peter
 
Not to name drop..... David Antscherl (in our local model club) once showed me that a dab of wood glue in the crack and a light sanding to move the sawdust into the glue made the crack disappear like magic.
 
Of course, he has a magic touch, and years of experience!
Try this on a test set up of two pieces of scrap before doing it on your model to see if it works for you.

I'm not sure of your question. That's a relatively easily planked bow shape. It appears the model builders pictured simply ran their plank ends forward of the stem line and then cut off the excess to the bow rabet. The practice then is to glue a strip of wood bent to the leading edge of the bow and sand it to a fair rounded leading edge.
 
As for planking, read up on what Chuck Passaro has shared about planking. It's the best tutorial on the subject I know of. https://modelshipworld.com/forum/98-planking-downloads-and-tutorials-and-videos/
 
As the original vessel hull was built of steel, I doubt you will be finishing the wooden model planking bright, so the good news is that fairing compound will cover a multitude of planking errors as long as you get the basic shape right.

The Pride of Baltimore has a running main topmast backstay that would be tensioned when the gaff topsail is set.  She does not have a backstays leading to the top of the main mast.  Under working sail, without the gaff topsail set,  she is, therefore, capable of sailing without a backstay.
 
She is actually Pride of Baltimore II, the first Pride was lost off the Barbados in 1986.  In designing the second Pride, naval Architect Thomas Gillmer modified the underwater hull lines to increase stability but did not change her rig to add backstays.
 
Another example would be the Schooner Yacht America.  Her heavily raked masts were not fitted with backstays.
 
Roger

Dry heat is all you need. There is no need, nor point to using, steam or moisture of any kind when bending wood unless you have to, and that's probably almost never when modeling. The steam or other moisture only serves the purpose of transmitting the heat to the wood. Given the size of the pieces in full size boat building, steaming in a steam box is a good way to heat the wood through and through in order to soften the lignin in the wood which is what it is all about. Even so, dry heat is also used where possible, to avoid the hassles involved in dealing with steam and moisture. (The gondola builders of Venice use open fires to heat their planks for bending.) But why get wet if you don't have to and when you can put the heat exactly where you want it and easily apply more as you need it when bending the piece?
 
A clothes iron as Chuck uses works very well for heating strip wood to bend it on the flat ("edge setting" in boat building parlance.) and you don't have to mess with steam or boiling water which risks burns and wets the wood which then requires drying time and, if moisture remains, often makes gluing difficult. Actually, if you use PVA adhesive to glue your planks in place, applying heat with an iron on the outside of the plank at each glued frame or bulkhead will dry the PVA, effecting a much faster setting time. To obtain curves in another direction (not exactly a "compound curve," which something different than what you are talking about here) a clothes iron can be used, but a heated, curved former is probably more effective. Use the forum search engine. There are posts on ingenious ways to do this. Some use tin cans heated on the inside with a propane torch as a former. Some use a pipe heated with a torch on the inside. Some apply heat from an electric curling iron and press the wood into a form cut from a block of wood. Myself, I am partial to the now-no-longer-made-but-sometimes-available-on-eBay Aeropicola plank bending iron, which is something like an electric soldering iron with a French Curve shaped head on it that allows bending various radii with it. There are other types of electric plank benders sold today that do the same, although not as well, if reports are accurate. 
 
As Chuck has so accurately said, you need to bend your planks, or any bent piece, for that matter, to shape before you try to fasten them up. You can use the frames or bulkheads as forms for bending, but don't expect the planks to stay in place unless they are bent to shape before gluing in place.
 
I would greatly encourage anybody who wants to bend wood to read "the Bible:" Bending Solid Wood to Form (1957) U.S. Dept. of Agriculture - Forest Service. (39 pages.)  https://www.fpl.fs.fed.us/documnts/usda/ah125.pdf  Bending wood is a lot easier when you understand the science and mechanics of what you are doing. 
 
  https://www.ebay.com/itm/AEROPICCOLA-Torino-WELLER-SP40-Electric-Plank-Bender-Tested-Works-Italy/383829086822?hash=item595dff1266:g:DhoAAOSwnRpfvwFq   There's an Aeropiccola plank bending head mounted on a Weller soldering iron for a "buy it now" price of $40.00 on US eBay. I suppose the fact that the head is mounted on an aftermarket soldering iron makes a difference for some reason I can't fathom, since the Italian originals were mounted on Italian soldering irons that were nearly identical to the Weller, which may even be of higher quality, for all I know, but these suckers have been listing on eBay for $75 to $100 (solely because nobody is making them anymore) and anybody who has any plank bending to do would be nuts not to grab this one like right now if not sooner. 

I'm not sure of your question. That's a relatively easily planked bow shape. It appears the model builders pictured simply ran their plank ends forward of the stem line and then cut off the excess to the bow rabet. The practice then is to glue a strip of wood bent to the leading edge of the bow and sand it to a fair rounded leading edge.
 
As for planking, read up on what Chuck Passaro has shared about planking. It's the best tutorial on the subject I know of. https://modelshipworld.com/forum/98-planking-downloads-and-tutorials-and-videos/
 
As the original vessel hull was built of steel, I doubt you will be finishing the wooden model planking bright, so the good news is that fairing compound will cover a multitude of planking errors as long as you get the basic shape right.

I have a natural science background and grew up in a natural science-househould. So, the natural thing for me was to make measured drawings, cut pieces according to the dimensions on the drawings and then assemble ... but often this did not work, perhaps due to poor manufacturing tolerances. I learned from watching craftsmen, who tend to cut pieces somewhat oversize and then fit them. Not the most efficient way in a production process, but very effective in an artisanal context - and shipmodel building is an artisanal process.

An erudite and practical view of this topic, Bob. Watch YouTube vids of boatbuilders at work. Craftsmen share a lifetime's experience, confirming your comments.

@Bob Cleek thanks for your clear and realistic explanation. Things are (or were) exactly as you said also in aircraft construction where I have some background. I smile when I read about confrontational discussions based on measurements taken directly from assembly drawings. As you said, the only reliable measures in drawings are the ones reported in writing.
Thanks and best regards,
Dan.

Adding to Eberhard and Dr.PR's comments, this discussion reminds me of something my late boatbuilding mentor, a older fellow who'd been one of the last to have gone through a traditional trade apprenticeship and had run a boatyard of his own for perhaps fifty years, said to me on the subject: "A house framing carpenter cuts to the nearest quarter inch, a finish carpenter cuts to the nearest thirty-second of an inch, and a boat builder cuts to the nearest boat." His point was that it isn't the measurements that matter, but rather the fit of the piece to the ones next to it, so forget about the dimensions on the plans and pay attention to what you are fitting together.
 
Any sort of ship or boat plans, at least until the advent of CAD, are never absolutely accurate. What they are, really, is simply "scaled plans for drawing full scale plans." You can't draw a scale line fine enough, even at 1:48. Back in the day, they'd draw the lines of a 150' ship on a six or seven foot long piece of drafting vellum and the scale lines drawn would still be so wide if blown up to full scale that you couldn't take accurate measurements from the plans. While at modeling scales, the problem isn't as great, how often do we see plans drawn to 1:48, even? The rule in full size engineering is always that measurements are never to be taken from the drawings, but rather must be taken from the notation of the distance on the drawing. In modeling, we can cheat somewhat, but only if we "build to the boat" and not to the plans. What the pre-CAD draftsmen did was to take up a "table of offsets" from the drawings with dividers and read the distances from scales, knowing that no matter how carefully they placed their divider points on the center of the line, the table of offsets would never be perfectly accurate. Indeed, if the offsets for a 150' ship were accurate to within an inch or two, they were quite good. 
 
The purpose of the table of offsets was to enable the loftsman to loft the patterns for the ship full size. The loftsman takes the table of offsets and the lines drawings and uses these to draw the vessel full size on the lofting floor. When doing so, the loftsman uses battens to spring fair curves, using the offsets as a guide, but the offset points are rarely all on the fair curve sprung with the batten. (There are many tricks to the loftsman's trade. In "fairing the lines" from the draftsman's offsets, the loftsman uses the "diagonals" to test the accuracy of the lofting, for example. Further discussion of this is beyond the scope of this post, but for those interested, Lofting, by Alan Vaitses is highly recommended.) The loftsman trusts the batten, not the draftsman's offset measurements to develop the full size patterns for the shape-defining parts of the ship. Only once in a while, when there are a number of identical vessels to be built, will you get lucky and find that a loftsman has generated a corrected table of offsets from the full size lofting that are "tighter than a gnat's ***." In this case, there will usually be a notation on the table of offsets like "Corrected offsets." or "Offsets as lofted." Otherwise, the offsets will have to be "faired" on the loft floor.
 
The loftsman's full size patterns were usually only those essential to get the vessel "in frame." From there, the "wood butchers" "built to the ship," not to the plans. They'd set up a few basic frames, sometimes as few as as a midship frame at the widest beam and a couple forward and aft of that, plus a stem and transom. Then they'd tack battens sprung across the faces of these frames and the resulting "basket" defined the shape of all the frames in between. In such fashion, a fair hull would be constructed. This is sort of the way planked models used to be built, although once in a while, an author would draw up a full set of frames and publish them for modelers to use, as we see in the old modeling books by Davis and his contemporaries.
 
Today, CAD makes it possible, in theory, at least, to generate far more accurate drawings and it seems modelers are seduced by CAD and then find themselves sucked into believing they have to become micro-machinists using extremely accurate (and expensive) machines with DRO, or even CNC, to turn out parts accurate to .0005 if they want to build a good model, even from a kit, but this isn't so. "If it looks right, it is right." was the old time ship builder's maxim and it serves the modeler as well in miniature as it did the old timers working in full size. The old timers didn't have to worry about cutting each side perfectly square and to exact size when making a box. They just cut half of the sides a bit large and when the box was built, they planed the overhangs on the edges to fit, yielding a perfectly jointed cube. I'm not knocking CNC, for it certainly has it's place. (We wouldn't have IKEA knock-down furniture without it!) For building one-off models, though, the old fashioned measuring tools are more than sufficient and often much less expensive, not to mention a joy to own and even collect. Our goal is to create a compelling impression of reality in miniature. That doesn't always mean NASA-level tolerances in our measurements. (Even at that, John Glenn orbited the earth in a rocket ship designed with slide rules!) Sometimes, even slight deviations from exact scaling, such a a smidgen smaller rigging lines, can actually produce a more compelling impression of reality than perfectly sized ones, and that's when modeling becomes an art and not just a craft. So as the man says, "Don't sweat the small stuff."
 

Adding to Eberhard and Dr.PR's comments, this discussion reminds me of something my late boatbuilding mentor, a older fellow who'd been one of the last to have gone through a traditional trade apprenticeship and had run a boatyard of his own for perhaps fifty years, said to me on the subject: "A house framing carpenter cuts to the nearest quarter inch, a finish carpenter cuts to the nearest thirty-second of an inch, and a boat builder cuts to the nearest boat." His point was that it isn't the measurements that matter, but rather the fit of the piece to the ones next to it, so forget about the dimensions on the plans and pay attention to what you are fitting together.
 
Any sort of ship or boat plans, at least until the advent of CAD, are never absolutely accurate. What they are, really, is simply "scaled plans for drawing full scale plans." You can't draw a scale line fine enough, even at 1:48. Back in the day, they'd draw the lines of a 150' ship on a six or seven foot long piece of drafting vellum and the scale lines drawn would still be so wide if blown up to full scale that you couldn't take accurate measurements from the plans. While at modeling scales, the problem isn't as great, how often do we see plans drawn to 1:48, even? The rule in full size engineering is always that measurements are never to be taken from the drawings, but rather must be taken from the notation of the distance on the drawing. In modeling, we can cheat somewhat, but only if we "build to the boat" and not to the plans. What the pre-CAD draftsmen did was to take up a "table of offsets" from the drawings with dividers and read the distances from scales, knowing that no matter how carefully they placed their divider points on the center of the line, the table of offsets would never be perfectly accurate. Indeed, if the offsets for a 150' ship were accurate to within an inch or two, they were quite good. 
 
The purpose of the table of offsets was to enable the loftsman to loft the patterns for the ship full size. The loftsman takes the table of offsets and the lines drawings and uses these to draw the vessel full size on the lofting floor. When doing so, the loftsman uses battens to spring fair curves, using the offsets as a guide, but the offset points are rarely all on the fair curve sprung with the batten. (There are many tricks to the loftsman's trade. In "fairing the lines" from the draftsman's offsets, the loftsman uses the "diagonals" to test the accuracy of the lofting, for example. Further discussion of this is beyond the scope of this post, but for those interested, Lofting, by Alan Vaitses is highly recommended.) The loftsman trusts the batten, not the draftsman's offset measurements to develop the full size patterns for the shape-defining parts of the ship. Only once in a while, when there are a number of identical vessels to be built, will you get lucky and find that a loftsman has generated a corrected table of offsets from the full size lofting that are "tighter than a gnat's ***." In this case, there will usually be a notation on the table of offsets like "Corrected offsets." or "Offsets as lofted." Otherwise, the offsets will have to be "faired" on the loft floor.
 
The loftsman's full size patterns were usually only those essential to get the vessel "in frame." From there, the "wood butchers" "built to the ship," not to the plans. They'd set up a few basic frames, sometimes as few as as a midship frame at the widest beam and a couple forward and aft of that, plus a stem and transom. Then they'd tack battens sprung across the faces of these frames and the resulting "basket" defined the shape of all the frames in between. In such fashion, a fair hull would be constructed. This is sort of the way planked models used to be built, although once in a while, an author would draw up a full set of frames and publish them for modelers to use, as we see in the old modeling books by Davis and his contemporaries.
 
Today, CAD makes it possible, in theory, at least, to generate far more accurate drawings and it seems modelers are seduced by CAD and then find themselves sucked into believing they have to become micro-machinists using extremely accurate (and expensive) machines with DRO, or even CNC, to turn out parts accurate to .0005 if they want to build a good model, even from a kit, but this isn't so. "If it looks right, it is right." was the old time ship builder's maxim and it serves the modeler as well in miniature as it did the old timers working in full size. The old timers didn't have to worry about cutting each side perfectly square and to exact size when making a box. They just cut half of the sides a bit large and when the box was built, they planed the overhangs on the edges to fit, yielding a perfectly jointed cube. I'm not knocking CNC, for it certainly has it's place. (We wouldn't have IKEA knock-down furniture without it!) For building one-off models, though, the old fashioned measuring tools are more than sufficient and often much less expensive, not to mention a joy to own and even collect. Our goal is to create a compelling impression of reality in miniature. That doesn't always mean NASA-level tolerances in our measurements. (Even at that, John Glenn orbited the earth in a rocket ship designed with slide rules!) Sometimes, even slight deviations from exact scaling, such a a smidgen smaller rigging lines, can actually produce a more compelling impression of reality than perfectly sized ones, and that's when modeling becomes an art and not just a craft. So as the man says, "Don't sweat the small stuff."
 

Adding to Eberhard and Dr.PR's comments, this discussion reminds me of something my late boatbuilding mentor, a older fellow who'd been one of the last to have gone through a traditional trade apprenticeship and had run a boatyard of his own for perhaps fifty years, said to me on the subject: "A house framing carpenter cuts to the nearest quarter inch, a finish carpenter cuts to the nearest thirty-second of an inch, and a boat builder cuts to the nearest boat." His point was that it isn't the measurements that matter, but rather the fit of the piece to the ones next to it, so forget about the dimensions on the plans and pay attention to what you are fitting together.
 
Any sort of ship or boat plans, at least until the advent of CAD, are never absolutely accurate. What they are, really, is simply "scaled plans for drawing full scale plans." You can't draw a scale line fine enough, even at 1:48. Back in the day, they'd draw the lines of a 150' ship on a six or seven foot long piece of drafting vellum and the scale lines drawn would still be so wide if blown up to full scale that you couldn't take accurate measurements from the plans. While at modeling scales, the problem isn't as great, how often do we see plans drawn to 1:48, even? The rule in full size engineering is always that measurements are never to be taken from the drawings, but rather must be taken from the notation of the distance on the drawing. In modeling, we can cheat somewhat, but only if we "build to the boat" and not to the plans. What the pre-CAD draftsmen did was to take up a "table of offsets" from the drawings with dividers and read the distances from scales, knowing that no matter how carefully they placed their divider points on the center of the line, the table of offsets would never be perfectly accurate. Indeed, if the offsets for a 150' ship were accurate to within an inch or two, they were quite good. 
 
The purpose of the table of offsets was to enable the loftsman to loft the patterns for the ship full size. The loftsman takes the table of offsets and the lines drawings and uses these to draw the vessel full size on the lofting floor. When doing so, the loftsman uses battens to spring fair curves, using the offsets as a guide, but the offset points are rarely all on the fair curve sprung with the batten. (There are many tricks to the loftsman's trade. In "fairing the lines" from the draftsman's offsets, the loftsman uses the "diagonals" to test the accuracy of the lofting, for example. Further discussion of this is beyond the scope of this post, but for those interested, Lofting, by Alan Vaitses is highly recommended.) The loftsman trusts the batten, not the draftsman's offset measurements to develop the full size patterns for the shape-defining parts of the ship. Only once in a while, when there are a number of identical vessels to be built, will you get lucky and find that a loftsman has generated a corrected table of offsets from the full size lofting that are "tighter than a gnat's ***." In this case, there will usually be a notation on the table of offsets like "Corrected offsets." or "Offsets as lofted." Otherwise, the offsets will have to be "faired" on the loft floor.
 
The loftsman's full size patterns were usually only those essential to get the vessel "in frame." From there, the "wood butchers" "built to the ship," not to the plans. They'd set up a few basic frames, sometimes as few as as a midship frame at the widest beam and a couple forward and aft of that, plus a stem and transom. Then they'd tack battens sprung across the faces of these frames and the resulting "basket" defined the shape of all the frames in between. In such fashion, a fair hull would be constructed. This is sort of the way planked models used to be built, although once in a while, an author would draw up a full set of frames and publish them for modelers to use, as we see in the old modeling books by Davis and his contemporaries.
 
Today, CAD makes it possible, in theory, at least, to generate far more accurate drawings and it seems modelers are seduced by CAD and then find themselves sucked into believing they have to become micro-machinists using extremely accurate (and expensive) machines with DRO, or even CNC, to turn out parts accurate to .0005 if they want to build a good model, even from a kit, but this isn't so. "If it looks right, it is right." was the old time ship builder's maxim and it serves the modeler as well in miniature as it did the old timers working in full size. The old timers didn't have to worry about cutting each side perfectly square and to exact size when making a box. They just cut half of the sides a bit large and when the box was built, they planed the overhangs on the edges to fit, yielding a perfectly jointed cube. I'm not knocking CNC, for it certainly has it's place. (We wouldn't have IKEA knock-down furniture without it!) For building one-off models, though, the old fashioned measuring tools are more than sufficient and often much less expensive, not to mention a joy to own and even collect. Our goal is to create a compelling impression of reality in miniature. That doesn't always mean NASA-level tolerances in our measurements. (Even at that, John Glenn orbited the earth in a rocket ship designed with slide rules!) Sometimes, even slight deviations from exact scaling, such a a smidgen smaller rigging lines, can actually produce a more compelling impression of reality than perfectly sized ones, and that's when modeling becomes an art and not just a craft. So as the man says, "Don't sweat the small stuff."
 

Adding to Eberhard and Dr.PR's comments, this discussion reminds me of something my late boatbuilding mentor, a older fellow who'd been one of the last to have gone through a traditional trade apprenticeship and had run a boatyard of his own for perhaps fifty years, said to me on the subject: "A house framing carpenter cuts to the nearest quarter inch, a finish carpenter cuts to the nearest thirty-second of an inch, and a boat builder cuts to the nearest boat." His point was that it isn't the measurements that matter, but rather the fit of the piece to the ones next to it, so forget about the dimensions on the plans and pay attention to what you are fitting together.
 
Any sort of ship or boat plans, at least until the advent of CAD, are never absolutely accurate. What they are, really, is simply "scaled plans for drawing full scale plans." You can't draw a scale line fine enough, even at 1:48. Back in the day, they'd draw the lines of a 150' ship on a six or seven foot long piece of drafting vellum and the scale lines drawn would still be so wide if blown up to full scale that you couldn't take accurate measurements from the plans. While at modeling scales, the problem isn't as great, how often do we see plans drawn to 1:48, even? The rule in full size engineering is always that measurements are never to be taken from the drawings, but rather must be taken from the notation of the distance on the drawing. In modeling, we can cheat somewhat, but only if we "build to the boat" and not to the plans. What the pre-CAD draftsmen did was to take up a "table of offsets" from the drawings with dividers and read the distances from scales, knowing that no matter how carefully they placed their divider points on the center of the line, the table of offsets would never be perfectly accurate. Indeed, if the offsets for a 150' ship were accurate to within an inch or two, they were quite good. 
 
The purpose of the table of offsets was to enable the loftsman to loft the patterns for the ship full size. The loftsman takes the table of offsets and the lines drawings and uses these to draw the vessel full size on the lofting floor. When doing so, the loftsman uses battens to spring fair curves, using the offsets as a guide, but the offset points are rarely all on the fair curve sprung with the batten. (There are many tricks to the loftsman's trade. In "fairing the lines" from the draftsman's offsets, the loftsman uses the "diagonals" to test the accuracy of the lofting, for example. Further discussion of this is beyond the scope of this post, but for those interested, Lofting, by Alan Vaitses is highly recommended.) The loftsman trusts the batten, not the draftsman's offset measurements to develop the full size patterns for the shape-defining parts of the ship. Only once in a while, when there are a number of identical vessels to be built, will you get lucky and find that a loftsman has generated a corrected table of offsets from the full size lofting that are "tighter than a gnat's ***." In this case, there will usually be a notation on the table of offsets like "Corrected offsets." or "Offsets as lofted." Otherwise, the offsets will have to be "faired" on the loft floor.
 
The loftsman's full size patterns were usually only those essential to get the vessel "in frame." From there, the "wood butchers" "built to the ship," not to the plans. They'd set up a few basic frames, sometimes as few as as a midship frame at the widest beam and a couple forward and aft of that, plus a stem and transom. Then they'd tack battens sprung across the faces of these frames and the resulting "basket" defined the shape of all the frames in between. In such fashion, a fair hull would be constructed. This is sort of the way planked models used to be built, although once in a while, an author would draw up a full set of frames and publish them for modelers to use, as we see in the old modeling books by Davis and his contemporaries.
 
Today, CAD makes it possible, in theory, at least, to generate far more accurate drawings and it seems modelers are seduced by CAD and then find themselves sucked into believing they have to become micro-machinists using extremely accurate (and expensive) machines with DRO, or even CNC, to turn out parts accurate to .0005 if they want to build a good model, even from a kit, but this isn't so. "If it looks right, it is right." was the old time ship builder's maxim and it serves the modeler as well in miniature as it did the old timers working in full size. The old timers didn't have to worry about cutting each side perfectly square and to exact size when making a box. They just cut half of the sides a bit large and when the box was built, they planed the overhangs on the edges to fit, yielding a perfectly jointed cube. I'm not knocking CNC, for it certainly has it's place. (We wouldn't have IKEA knock-down furniture without it!) For building one-off models, though, the old fashioned measuring tools are more than sufficient and often much less expensive, not to mention a joy to own and even collect. Our goal is to create a compelling impression of reality in miniature. That doesn't always mean NASA-level tolerances in our measurements. (Even at that, John Glenn orbited the earth in a rocket ship designed with slide rules!) Sometimes, even slight deviations from exact scaling, such a a smidgen smaller rigging lines, can actually produce a more compelling impression of reality than perfectly sized ones, and that's when modeling becomes an art and not just a craft. So as the man says, "Don't sweat the small stuff."
 

Any measurement taken from a printed drawing is subject to many errors. As mentioned above, line widths make finding dimensions problematic. Some printers do not actually print to scale and add some error to the measurement.
 
However, this isn't always a big problem. Things are not built to random dimensions. Engineers usually work in some units of measurement (inches, feet, millimeters, meters, etc.). For WWII US ships things were designed in feet, inches and fractions of inches (1/2, 1/4, 1/8 and occasionally 1/16 and 1/32). It is a lot simpler if the original units are metric!
 
Engineers usually don't design things in odd fractions, like 1.297 inches. If your measurement from the drawing scales to 1.297 inches (1:1 scale) it's a good bet that it really should be 1.25 inches. If you know the units of measure (inches, mm, etc.) the part was designed in you can correct some of the measurement errors by rounding to the nearest common fraction.

Paper drawings, as commonly used by shipmodelers, are not very accurate, so taking precise readings may not help you in the end, because errors of several measurements tend to end up. There are couple of strategies to overcome this:
 
- always take measurements working from the largest outside dimensions, working inward and make sure that subsequent measurment add up to the total of the outside measurement first taken
 
- redraw the parts in a 2D CAD or similar program from the readings taken from the paper copy; the result should look like the one on the paper and you can take the precise dimensions off the computer without having to worry about line thickness; you can add dimensions to your drawing as in a normal technical drawing, which is helpful for machining.
 
- a variant of the above is to scan (parts of) the paper drawing and copy this image into your drawing program; in another layer you can trace the outlines of the part you want to make and correct dimensions so that all parts fit together; this is today my usual method.
 
If I am working from paper drawings the old way, I am using an analog vernier caliper. I have very small one that is only 10 cm long and comes very handy for working on small parts.

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Kurt

American small fast sailing vessels of the period in question were notorious for being lightly rigged.  There are contemporary paintings of Chesapeake Bay Pilot Boats with masts that are completely unstayed no shrouds or stays.  The Baltimore Clippers were decendents of these small high speed Schooners.
 
There is an Admiralty drawing of a rigged longboat in W.E. May’s book on ships boats.  This sloop rigged boat with raked mast has no backstays

Hence the once common machinist's magnifiers:
 

Probably not. Some may have carried them for temporary rigging, particularly from the the point(s) where square sail yards crossed the mast to prevent the mast bowing when running in heavy weather.

The answer to your question depends upon the particular vessel and is dependent in large part to the size of the vessel. Smaller vessels may run the fall of a running backstay to a turning block fastened to the deck and then aft to a lever which tensions the backstay when it is thrown down. On larger vessels, a purchase is rigged which may be arranged in any number of ways, but generally with the weight of the blocks kept as low as possible. Running backs may also have a hook at their lower end to which a tackle can be attached. Unhooking the backstay then permits it to be run forward and lashed to the after shroud to keep it out of the way when not in use.
 
If you could post a picture or sailplan of the vessel, you'd probably get the best answer that way. 
 

Or that the found object - in fact, a pulley or sheave - has been 'decorated' with line. The condition of the line (and in particular, the worming) does not look as old as the sheave!

Probably not. Some may have carried them for temporary rigging, particularly from the the point(s) where square sail yards crossed the mast to prevent the mast bowing when running in heavy weather.

With their heavily raked masts would these vessels have needed backstays?
 
 

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