Dutch heavy frigate ca. 1700 – engineering or carpentry ‘snowman’ making?

[Waldemar]

 

Since existing publications, including academic ones, have actually been creating a Universe-sized research void in the field of period ship design, particularly in the North Continental/Dutch tradition, for several decades now, it is worth taking a look at the design of Dutch origin, which I personally date to the late 17th and early 18th centuries and, according to design criteria, from an era before the widespread adoption of design diagonals, at least in the Netherlands.

 

The design in question is that of a 114-foot-long heavy frigate, graphically designed for construction using the bottom-first method, as clearly evidenced by the two design lines characteristic of this method: the edge of the ‘flat’ and the ‘boeisel’ line, the latter separating the carpentry zones of bilges and sides of the ship's hull.

 

In the archival description, the drawing is dated 1780, which must be perceived as an obvious mistake. The square tuck stern, the short beakhead, the double wales, the double master frame (somewhat retrospectively here), as well as the (prediagonal) design method itself clearly point to the decades just around 1700, i.e. quite close to when van Yk's work on shipbuilding was published in 1697.

Link to archive and reproduction of the plan (Dutch archives):

 

https://www.maritiemdigitaal.nl/index.cfm?event=search.getdetail&id=100199384

 

 

 

 

The renders below show the hull shapes of the Dutch heavy frigate ca. 1700 by using diagonals, waterlines and cross sections. Despite some concerns even before investigating the design method of this project, the resulting form can be considered very good in terms of its smoothness. Of note are only moderately sharp entry at the bow and also the run at the stern, as for a warship of this period.

Most interesting, though, is the conceptual method, which has not been described before. It is actually quite simple and the design sequence quite standard, nevertheless the result of this specific method is, among other things, the curved cross sections of the ‘flat’, which are hardly anywhere along the length of the hull straight lines as in other known designs. This should be clearly visible in the attached graphics, as well as in the original plan itself.

 

 

 

 

 

 

 

Main dimensions / keel assembly / lengthwise division

 

The sequence of the initial design phase is largely the same as described for the French heavy frigate of 1686, with the major exception that in this design the double master frame was already applied, as in the project of Dutch 72-gun ship described in another thread:

 

– the length of the ship was determined by summing up the spacing between the gun ports, the width of the ports themselves (possibly 12-pounders), and their distances from both ends of the hull,
– the keel is realistically curved, which is later reflected in the process of forming the contours of the leading frames,
– the sum of the rakes of the two posts is 1/11 of the length of the ship, and their ratio to each other is 1:3, resulting in a very small rake of the stem,
– the length of the ship between perpendiculars has been divided into nine equal parts,
– the lengthwise placement of the double master frame has been set, respectively, at 3/9 and 4/9 of the hull length,
– the placement of the „virtual” single master frame, needed only for setting up the main longitudinal design lines (“flat”, max. breadth, top lines, decks), was set halfway between the fore and aft master frames, resulting in the greatest breadth of the ship at this single master frame; its longitudinal position falls very roughly at 1/3 of the keel length.
– the depth in hold value was set at a textbook 1/10th of the hull length,
– the level of the waterline at the (single) master frame was obtained by adding to the depth in hold the height of the gun port sills above the deck (here 2 feet) and then subtracting their intended distance from the water level (here 3 feet 7 inches). Finally, the design waterline was angled to a 3-foot trim.

 

 

 

 

Line/edge of the ‘flat’ (green)

 

This line is the basis for shaping the underwater part of the hull. Deadrise (at the master frame) is large and is as high as 1.5 feet, measured from the realistically curved keel. At the fore, the line of the „flat” terminates at the intersection of the perpendicular with the waterline, and at the stern post at the level of height of the tuck, which in turn has been also set at the height of the design waterline. For both halves of the hull, it is a logarithmic curve, in both projections, which translates into quite full, or maybe better round shapes.

 

Line of the greatest breadth (blue)

 

At the master frame, the distance of this line from the waterline has been set at a quite standard value of 2 feet. This distance is one of the most important factors affecting the lateral stability of the ship. In the sheer view, both arcs of this line are tangent to an auxiliary line parallel to the waterline (dashed line). It is perfectly parallel to the wales, or perhaps more correctly – the wales would be subsequently made perfectly parallel to this line.

 

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Of note is the very extensive use of logarithmic curves in this project. Contrary to the popular belief, it is one of the easiest curves to obtain, and no knowledge of theory is needed at all for their employment, just a familiarity with a straightforward division operation. For the same reason, logarithmic curves are also very practical and easy to use in real scale, for example to trace the contours of the frames without first drawing up a paper plan.

 

 

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It may be prefaced here that the use of the conceptual method found in this plan of Dutch origin and presented below is not necessary for less demanding applications such as recreational construction of display models. Instead, the suggestion by scholars and well-known authors to mechanically copy the contours found on the original plans and then to proceed to smooth the hull shapes by eye can be used. However, this alternative method adopted by even the best experts in the field is unlikely to give completely satisfactory results in this case due to the rather significant drawing inaccuracies and distortions of the original drawing, which will most probably lead to the generating of the proverbial ‘snowman’. In addition, this method does not explain the design methods of the ships of the period and will not always be quite suitable for vessels of other dimensions or proportions either.

 

 

Shaping the leading frames

 

The sequence and method of determining the contours of the leading frames is straightforward and is naturally based on the main design lines previously defined, i.e the line of the ‘flat’ and the line of the greatest breadth:

 

– the lines of the ‘flat’ (red colour) were plotted first. For the central frames these are horizontal straight lines, for the two outermost frames #1 and #7 they are also straight lines, but connecting the keel to the line of the ‘flat’, and for the last frame #8 a circle arc is employed for a smooth transformation of the hull shape towards the sternpost,
– the futtock sweeps are then plotted (blue colour). For the central frames these arcs are brought to half the half-breadth of the corresponding frames. For the outermost frames, they are defined differently (see attached diagram),
– finally, the two sets of previous elements are connected by bilge arcs (black colour) in such a way that they intersect the line of the ‘flat’, while maintaining tangency on both its ends. For the exceptions occurring on the extreme frames, see the attached diagram.

 

Actually, so much for obtaining perfectly smooth shapes in a remarkably simple way. However, it can also be added that the best radius of the curve for the ‘flat’ in last frame #8 could also have been obtained at the very end of the design process, already after the ‘boeisel’ line had been determined and thanks to the use of this line.
 

 

 

Finding the „boeisel” line

 

This line, except perhaps in the exceptional case of frame #8 mentioned above, was actually no longer of conceptual importance, although it could be practically useful to the carpenters directly building the ship, for the correct positioning of the frame elements and for dimensional control of the moulded hull shape. In this case, it was obtained by copying upwards the line of the ‘flat’ on the side projection (by about 3 feet 4 inches). Then, the coordinates of the points of its intersection with the already formed contours of the frames were transferred to the top projection and connected by a line. As can be seen in the diagram, this line does not separate the distinct geometric entities, but intersects both the futtock sweeps and the bilge sweeps.

 

 

 

As a general conclusion, I would also add that I personally do not see anything in this plan that could justify the claim of shipbuilding by eye. On the contrary, if one reads Witsen's and van Yk's work closely, as well as other documents from the period, such as business and legal agreements, it becomes clear that the information they contain must have had its origin in plans such as this (whether paper or mental). After all, even the customary formulae did not fall from the sky or were handed down by extraterrestrial beings.

 

That’s it. Thank you for your attention,

 

Waldemar Gurgul

 

Edited June 18 by Waldemar