Harold Hahn

[DAWarden-(Jaager)]

a set of ship curves may be hard to find but if you Google ship curves and you get an image of a set could you use that image and make a setcut out of plastic or wood?

When you are using a computer program to loft and it is the computer version of freehand connect the dots:
and your curves are not constrained by a computer program equation - spline, Boolean(?), that thing with two external control points.
Straight up mouse or pen freehand curve gets sloppy with me. (I use a raster based drawing program, so any curve is a series of facets - which I can live with because a plane. rasp, file, mechanical and then hand sanding, scraper invariably turns it smooth)
Import a photo of each curve into your drawing program.
Use the magic wand to remove the background. Just have the black line of the curve on its layer.
The proper curve to connect the three points - rotate, scale, move the curve layer.
Select the segment of the curve that you want and save to its own layer.
Then merge that layer with the frame layer.

 

[DAWarden-(Jaager)]

This gives you a guide for drawing the frame between the two red frame lines.

The curve between the two guide frames is not an arc. It is a curve that drops off ever more rapidly. But the good part with doing this is that the curve that is drawn is fatter than it would be if it was plotted points. Fatter is good. When the hull is worked into a continuous smooth surface, the extra fat part will go away.

 

[-Waldemar-]

Half Models: Half models were the principal and often the only design tool used by many shipbuilders during the Nineteenth century in the USA and in parts of Great Britain. This excludes vessels designed for naval service by government bureaucracies where lines drawings were made. Offsets were measured from the models and sent to the mould loft floor where the design was refined. This practice was still used here on the American Great Lakes into the first quarter of the twentieth century. As Bob mentions Nathaniel Herreshoff refined this process with the invention of a specially designed machine using dial indicators to measure offsets. Many lines drawings available to ship model builders have been drawn from existing half models and sometimes tables of offsets. They (the drawings) were not used to build the ship.

Yes, the middle decades of the 19th century mark a clear separation between two quite different eras with different characteristics and practices, one might say. As a curiosity, I would like to add that in 18th-century France, for example, naval shipyards were also often sent only tables of offsets (based on an officially approved design), with the difference that these tables were based on paper plans, as opposed to measurements of half-models.

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[Bob Cleek]

QUESTION

a set of ship curves may be hard to find but if you Google ship curves and you get an image of a set could you use that image and make a setcut out of plastic or wood?

In theory, yes. In practice, no.

The irregular curve shapes of various types are high tolerance drawing templates. They work in conjunction with one another to produce fair irregular curves.



The reduced size drawings of irregular curve sets copied from drafting instrument supply company catalogs are probably not sufficiently accurate to use as patterns if enlarged to full size.

A few years ago, a fellow created a "go fund me" site to produce the full set of ship's curves in acrylic, cutting them out with a laser cutting machine. His project had to be abandoned because he discovered that the cost of laser cutting production was too expensive. Mass production was not sufficient to create economies of scale which would put the project into the black. There wasn't enough of a market for the them anymore.

 

[Roger Pellett]

Waldemar, The model that I am currently building is probably an example where the shipyard that built the ship never saw a complete lines drawing.

The Great Lakes Steamship Benjamin Noble was designed by the Cleveland, Ohio design office of the American Shipbuilding Company in 1908. She was built by their Wyandotte, Michigan shipyard located 150 or so miles away. No complete lines drawing is known to exist. Instead there is a table of offsets and a lines drawing of just her fantail stern. To build the model it was necessary for me to make a lines drawing using the table of offsets.

The original lines drawing or half model was probably destroyed by the design office. The drawing package including the table of offsets and fantail stern drawing sent to the shipyard to build the ship was saved and ultimately donated to a museum.

Roger

 

[Greg Davis]

What Harold meant when he said options for introducing detail is his plans are designed so a builder can alter the framing without having to change the framing system or redrawing frames.

I find this extremely interesting!


Non-related to the framing; at some point can you speak to Mr. Hahn's tree nailing principles? I have often wondered why he chose to use the size and number of such. At this point, I am going to guess that it was an artistic choice he made since it is clear that his skills were that he could have reduced the diameter and increased the number. The other competing guess I have made is that the tree nails are as they are for structural reasons.

 

[Bob Cleek]

Therefore, personally, generally speaking, I see the use of half-models in the ship design process more as an aid than as the (most important) basis for obtaining hull shapes, at least in the context of fully professional design centres (just as today, 3D models of designed objects are made as an aid to verify certain features or simply to facilitate certain design processes). Furthermore, I see no reason to view 19th-century American practices as in any way less advanced than those of other centres of this kind, maybe except in the case of semi-professional shipyards and/or less demanding projects, for which it was not worth engaging fully professional, advanced design procedures.

It would appear that your personal opinion as stated here would place you outside the great majority of maritime historians and naval architects. They are still using models in towing tanks and wind tunnels as important tools for obtaining hull shapes.

The analysis of old designs preserved in graphic form actually never involves drawing a single line or, even less so, a larger set of lines that immediately fit together.

Would it not appear that this was the loftsman's job to do it at full scale after fairing the lines on the loft floor? One would not seem to get very far analyzing "old forms preserved in graphic form" when those "old forms were never exactly preserved in graphic form at all," such "graphic form" being the loftsman's patterns which were promptly put to better use heating the loft once they'd served their purpose of turning their "graphic form" into an actual piece of the ship.

Similarly, I am also not sure whether the tempting recipe for ‘quick’ line drawing is always effective in the long run, because in practice it turns out that model makers have notorious problems with sloppy plans, which they quite often complain about, and these are usually the results of manual drafting and in a hurry. As a result, they are faced with a need of correcting these errors in a woodworking way, often quite troublesome and time-consuming, and not always yielding satisfactory outcome, which calls into question the apparent economy applied at the stage of drafting the modelling documentation. They may simply give up on these corrections, but are left with quite noticeable, sloppy shapes of their model hulls, or they correct them at the woodworking stage of model construction, aiming at least to achieve fairness, but such operations are inevitably carried out at the expense of shape consistency, i.e. the final shape of the model hull drifts towards a more or less ‘random’ entity. While indeed this is probably not something that keeps too many hobbyists awake at night, but it is at least worth being aware of such consequences, if it matters to anyone .

Quite true and shame on them. This "sloppiness" is not only a function of a lack of drafting skill and attention to detail, but also, and perhaps primarily, because of current design practices in the commercial ship model kit industry, including, but not limited to "plank on bulkhead" hull construction. For reasons of crass commercialism, many kit manufacturers actually encourage and support such sloppiness and lack of attention to detail. Finally, whether in the case of a full-scale ship or a scale model, the fairing of drawn plans is and always will be the builder's, rather than the designer's responsibility and the builder relies in the first instance on the loftsman's skill to create the patterns for the pieces that will be assembled based upon drawn plans which are always subject to being faired in the loft. Of course, the vast majority of kit builders who identify as "scale ship modelers" haven't the slightest clue what lofting is, let alone how to do it. If you don't believe that. As one what a diagonal is and what it's used for. You're right, they don't lay awake at night worrying about it because they don't even know how wooden vessels were (and still are) built, let alone designed, in real life, in many cases they've never seen a high-quality scale ship model and mistakenly believe that's a picture of one on the cover of the ship model kit box they bought, and the kit manufacturers have created a false impression of "quality" that's got all of them congratulating each other on social media for each other's "awesome" models.

Might I suggest that CAD perhaps unwittingly enables such mediocrity in the modeling field by making available "pictures" than can be rotated and tipped and viewed from all directions in three dimensions by those with inadequate education and background to truly understand them. I doubt you will find the same level of sloppiness in models built by those who know how to "read" drawn plans in two dimensions and are able to "see" three-dimensional objects when looking at an old-fashioned draftsman's work. I know CAD is a very handy, powerful tool, but I'm not surprised by your frustration with manual drafting when "analysing preserved period plans and studying old design methods." It's always been my experience that such primary-source historical research is best done using the language and tools contemporary with that source material's time and place.