I agree that it should be possible to draw the keel and sternpost according to the above mentioned measurements but you also need the general description van Yk gives. My question is, is there anybody who tried that? On paper or in the computer? And I disagree with point 1 and 2. I find the writing of van Yk quite clear. But it always will be an interpretation. The measurements of these ships depend on each other and this interdependence shows throughout van Yk's book. And he is very consistent in that, much more than Witsen. For instance, the depth of the rabbet in the keel reappears when van Yk gives the thickness of the sternpost aft at the keel. And with that the total thickness of the stern and garboard strakes. And with that the thickness of the rudder. And so on. All these measurement are interrelated and this relationships are shown throughout his book. Concerning the remark of the margin the shipwright has concerning the certers, there is no margin. The certers in Cornelis's book are the way the mentioned ships are built. You can find proof of that in almost every certer he presents. And van Yk mentions this himself. It is even possible to trace some of the names and history of the ships according to the three main measurements and the given year the ship was built. There is a margin in the general way van Yk speaks about the different parts of the ship in the subsequent chapters. But not in the certers. So you can regard these certers as 'plans as built'.
As I understand the general question of this thread is how relevant the books of Nicolaes Witsen and Cornelis van Yk are for the geometry of the Vasa? Since the Vasa was built (partly) by Dutch shipwrights there is a fair chance the methods used could be derived from the mentioned books. To be able to make a comparison you need to make a reconstruction using the information provided by both authors. In this thread Jules published a translation in English of the measurements of keel, stem, stern and rabbet of a 172 feet (48,69 meter) ship mentioned in chapter 24 of van Yks book. I will try to give a reconstruction of the stem(post) using these measurements and the method to establish the profile of the stem as van Yk explains in his book. I will do that in a few separate posts. Before I continue I have to give a small introduction. When a shipwright wants to build a ship he needs to know five things: material (what is it made from), size (how big is it, measurements), shape (what form does it assume), sequence (what do you do first) and procedure (how do you do it). Together these understandings constitute a recipe. I think every traditional craft can be described using these five understandings. In the following posts I will give a reconstruction of the profile of the stem using the aforementioned measurements of this 172 feet ship while referring to these understandings. I will also give some comments and reveal some assumptions I make in the process. First it might be wise to say something about the certer these measurements are taken from. According to this certer this ship was built in 1629. So this ship was a contemporary of the Vasa. This is a very interesting certer for several reasons. First of all it concerns a ship van Yk couldn’t have known. The majority of the certers in chapter 24 of his book are from or around the sixties of the seventeenth century which was probably the time van Yk himself was learning the trade as a teenager. So he probably has seen most of these ships being built and he even states that he worked at some of them. Second, it is an unusually large ship. Unfortunately I couldn’t trace this ship back to a name or to a place where is was built. Van Yk doesn’t say a word about the origins of this certer. That is, by the way, a peculiar property of all the ships van Yk mentions, they lack a name although van Yk must have known these names. Witsen mentions many names of ships in the certers he presents. It is very probably a merchant ship, nothing indicates this was a warship. The descriptions of the different decks in this ship show this was indeed a merchant ship. It could very well have been a ship built in Middelburg for the VOC chamber of Zealand. But that is an educated guess. Third, it is one of three certers in chapter 24 where van Yk gives an enormous amount of information which makes it possible to make a comparison concerning the geometry in time since the other two ships were built in 1664 and 1667.
The specifications of the stem for the 172 feet ship are as follows:
The stem, measured along the curve, was long 47’, 13,31 meter In the square, from the upside of the keel 32’, 8”, 9,27 meter Fell forward 34’, 9,63 meter Was thick 1’, 6”, 0,44 meter Was wide, above 3’, 0,85 meter In the middle 2’, 6”, 0,72 meter Below 3’, 6”, 1,00 meter The inner rabbet was thick 41/2”, 116 millimeter De rabbet was wide 4”, 103 millimeter Was deep 31/2”, 90 millimeter The stem was below on each side, hewn tapered 1”, 26 millimeter
The first assumption I make is these measurements are given in Amsterdam feet. One Amsterdam foot is 0,2831 meter. This assumption is based on the fact that all measurements van Yk presents, are given in Amsterdam feet unless stated otherwise. He uses for instance the Rhineland foot for the description of smaller inland shipping vessels. However, the VOC introduced in 1650 the Amsterdam foot as the standard foot for all VOC ships to be built accordingly. Since this ship is built in 1629 the foot size used in this certer might well be another than the Amsterdam foot. If the Rotterdam foot (0,2823 meter, also divided in 11 inches) was used this ship would be 0,14 meters shorter. Van Yk doesn’t mention anything about the use of another foot size for this certer. Van Yk does mention and shows in his book the existence of different sizes and divisions of the feet used in different parts of the Dutch Republic. Remarkably enough, in this overview, he doesn’t mention the Rotterdam foot which was used in the region he used to work. Maybe he did so because the two foot sizes are almost equal. They differ 8/10 of a millimeter per foot.
Before starting on your journey, I want to draw your attention to the fact that the amount of traffic on this forum is very, very low in the last year. So: your reconstruction will be interesting to see, but I doubt it willbe seen by very many if posted here. Perhaps you should try and find another place to present your work, where more people can read it, and gove you feedback (in case you want any).
I don't know any of your background, but there exist a rather active german forum (segelschiffsmodellbau) and a very active american one (modelshipworld). The latter more focussed on modelbuilding, the first alsosome members active in the research-area.
And a last one to Van Ijk, although being easier to read, and consistent in what he writes, he is by far not complete in what he writes. All reconstructions I know of, are therefore 'Witsen-based'. And with respectto Wasa, I don't think those two books were used as 'handbooks' Both are written for a rather lay,an public (Witsen himself was a lay,an, and not a shipwright)
Are these measurements in the certer of this 172 feet ship for the stem comparable to the stem of the Vasa? Since I do not have the actual measurements and shapes of the stem of the Vasa at my disposal I will use the ‘plank expansion drawing’ of the port side of the Vasa which can be found on this forum, to project my reconstructions upon. First I had to crop the picture and subsequently import it in the computer drawing program (Rhino). After importing it I had to scale the drawing. The vertical lines in this drawing are spaced one meter from each other. So the red line at the bottom of the picture is a line with a length of 5 meters. The inner curve of the stem is not visible but I assume this curve runs parallel to the outer rabbet which is visible here as the ends of the strakes. Next we have to establish a profile of the stem using the given measurements for this 172 feet ship. And there we encounter the first problem. Witsen doesn’t give a method for establishing the profile of the stem. He merely states, ‘when the curve is as desired’. That is not much to go on. This is a recurring problem with Witsen. If you want to build a real full scale ship from scratch using the information from Witsen’s book you almost immediately get stuck. This starts with the keel. The rabbet in the keel for instance is a very important structure in the building process but Witsen barely mentions the rabbet. If you look at the five understandings I use as threads for my analysis, the last one, procedure, is the one which can only be described by an insider. Someone who masters the shipbuilding trade. This gives an idea about the basic difference between the books from Witsen and van Yk. An outsider like Witsen is able to record the things an outsider is able to: measurements, sequences, but how things are done is another matter. Van Yk is brilliant in describing procedures and he is the one who does give a procedure to establish the profile of the stem. However, there we encounter another problem.
This problem originates in the way the total length of the ship is constructed. Both Witsen and van Yk measure the total length of the ship between the perpendiculars from the front of the stem to the back of the sternpost. But this length is divided into three parts in the case of Witsen and four in the case of van Yk. The problem occurs at the stem. Witsen defines the rake of the stem as the distance between the front of the stem and the face end of the keel including the box scarf. Van Yk defines the rake as the distance between a certain point at the keel and the upper inner corner of the stem. So van Yk begins to construct the inner profile of the stem. From that profile he works his way forward, so the width of the stem at the top has to be added to the total length of the ship as illustrated at the attachments. In other words, Witsen gives the rake measured at the outside and van Yk gives the rake measured at the inside of the stem which makes the given rakes in the two books quite incomparable. Since Witsen doesn’t provide a method for establishing the profile of the stem we only have the method van Yk presents. The construction of the profile of the stem as presented by van Yk has another consequence which has to do with the distribution of the different lengths of the keel parts and the joint between keel and stem. This has to do with the point at the keel where the height and rake of the stem are measured from. But that topic is beyond the scope of this thread. We can make a reconstruction of the stems profile of the 172 feet ship using van Yk’s method and compare this profile to the profile of the stem of the Vasa. But it is in no way certain the builders of the Vasa were using this method. Van Yk mentions the fact there are several ways of establishing this profile. Together with the fact that the profile of the stem depends heavily on the available pieces of wood and the master shipwright who is in charge, it is almost impossible to say anything definitive about the method and procedure they would have applied. The only way to establish something reliable is if there are written sources but to my knowledge they are absent.
The first thing to check is, if the height and rake of the stem of the Vasa correspond with the measurements for the 172 feet ship. Here I make another assumption. Apart from the assumption the measurements of this 172 feet ship are given in Amsterdam feet, another assumption is the fact this ship was measured the same way as Cornelis describes in his general descriptions. So the assumption is, the given rake in the certer of the 172 feet ship, is the rake from the inner profile of the stem. This is far from certain because, as we know, this ship was built before van Yk was even born. But there are indications the way these measurements are measured, correspond to the ships which were built in van Yk’s time. This needs some explanation. If you look at one of the five understandings I use, size, this can only be understood when you know how this measurement was taken and recorded. So there is another understanding, firmly connected to ‘size’ which is ‘direction’. Let me give an example. When van Yk describes the keel he mentions the joints and gives a length of these joints. But what he doesn’t say is how the length of these joints are measured. We almost automatically assume this direction is measured in the direction of the axis of the keel. But is there direct proof for that? There is also the possibility the length of the joint is measured over the oblique surface of the joint. I have never encountered anyone who pondered about these, in my opinion, quite fundamental questions. The same is true about the rake of the stem and how you measure that rake.
The height of the stem as given by Witsen and van Yk also can’t be compared. Both authors measure the height of the stem from the upside of the keel. But Witsen measures the height to the upper-outer corner and van Yk to the upper inner corner of the stem. The only thing that can be done with the measurements of the 172 feet ship is to assume the measurements of the stem are taken at the inside. There is one clue which justifies this conclusion. I will come to that later. If the measurements of height and rake of the stem of this 172 feet ship are taken from the inside these measurements can be compared with the drawing. To do that I first trace the profile of the stem so we can discard the plank expansion drawing. This is drawing one, the profile of the stem of the Vasa, rendered in blue. Next I draw two lines, the height and the rake at the inside of the stem of the Vasa. These lines are visible as green lines in drawing two. We also have the height and rake given for the 172 feet ship. These lines are visible as red lines in drawing two. The upper-inner corner of the stem is used as point of origin to be able to compare the height and rake. It is immediately clear these measurements don’t fit. Even if you take into account the stem of the Vasa is bigger than is visible here. If you assume the given height and rake are measured the way Witsen does, it is possible to place these measurements at the outside of the stem with the upper-outer corner as point of origin. This is drawing three. This also shows these measurements clearly exceed the height and rake of the stem of the Vasa.
Sorry, I should have expressed myself more precise. I was thinking that a shipreconstruction based on Van Ijk, may be of wider interest than for the relatively few active members here. It was not meant as an instruction to leave (although, on re-reasing I understand why you read it as such), it was actually written as an suggestion to seek a wider audience for a potentially very interesting topic Hope you'll accept appologies...
Apologies, of course, accepted. I understand now what you were trying to say. I know the other forums well. But, as you might have noticed, the people from the german forum who are interested in Dutch shipbuilding, and who speak english, came over here to have their discussions. And since Peter D.G. stopped publishing his Hohenzollern-model-build there, don't know what happened there, there's not a lot going on considering Dutch shipbuilding. As Philemon rightly remarks, the American site is excellent for English and French stuff. Dutch stuff, not so much: they actually do not care much. What I would like to see is that people who are really interested come over here. You are contributing on both forums. Invite them over here! Promote us, not them!
PS now I really have to start reading all the stuff Philemon put out there.
The measurements of the stem, height and rake, of the 172 feet ship clearly don’t match with the geometry of the stem of the Vasa. You can have all kinds of discussions if the point of origin at the keel is correctly placed, the used drawing of the stem of the Vasa is not complete, and so on but that still does not account for the quite substantial differences in size. For the height this is about 1,6 meters, the rakes differ about 1,5 meters. But how about the method van Yk gives to establish the profile of the stem? Van Yk describes two methods, one for a stem with a lesser height than rake and one for a stem with a lesser rake than height. The two methods are practically identical. The essence is to find the radius and the centre for a circular cut which constitutes the inner profile of the stem. This method can be tried using the measurements of the stem of the Vasa as presented in the former post. The rake of the Vasa is slightly larger than the height. Van Yk takes these two measurements perpendicular to each other, shown in the attached drawing as the lines AB and BC. Then van Yk draws a third line. This is shown as line AC. Perpendicular to this line van Yk draws a line from the middle of this line AC towards the lines AB and BC. The intersection of the oblique line with the extended line AB or line BC yields the desired centre D. With which extended line, AB or BC, this oblique line will intersect depends on the difference in length of the height and rake. Next van Yk takes a compass and draws a circle between point B and point C. This is the circle cut which constitutes the inner profile of the stem. This circle cut is drawn in the attached drawing together with the profile of the stem of the Vasa. The second attachment shows the original drawings of van Yk to explain his method for both cases.
The results of the former post, the profile yielded applying van Yks method to the height and rake of the stem of the Vasa, are intriguing. The actual curve of Vasa’s stem is more gentle than the constructed one. For comparison it is possible to give the computer a command to draw a circle through three points. Three points always define a circle. If you want to choose three points on the actual curve of Vasa’s stem, you can take point A and C, and as third point the middle of the inner curve of Vasa’s stem. The resulting profile, drawn in red, almost completely matches the curve of Vasa’s stem. This can be seen by the alternately visible blue and red colour of the two lines who cover each other almost completely. Furthermore, if you pinpoint the centre of this profile, this center is located almost exactly on the same line with which centre D was established using van Yk’s method. In the drawing the centre of the inner profile of Vasa’s stem is marked with a red cross and the original line is extended. This is pure coincidence. I did not intentionally work towards an outcome like this, so I am just as surprised as the reader might be. You may conclude this inner profile of the stem of the Vasa is indeed a circle cut. Due to the lack of pieces of wood which could deliver the desired curve you change the centre until a match is found. This was common in those days, to try to optimize the yield of the available pieces of wood as van Yk mentions himself several times in his book. However, I can’t be more conclusive than this. To be able to make a good analysis you need the shape and measurements of the whole stem, not just a part of it, as is the case here. There is another intriguing detail visible in the plank expansion drawing which is the joint of stem and keel. If I am not mistaken this is a standing plated, stopped or nibbed scarf. Exactly like the ones Cornelis shows in his construction drawings, displayed in the former post. For some ships Cornelis even gives the length of this joint. It doesn’t seem to be the construction Witsen presents with a box scarf, a joint which can’t contribute much to the constructional strength of keel and stem. On the other hand, the stem runs a fair distance over the keel towards aft, according to the drawings I have of the Vasa. But due to lack of precise information I don’t dare to say much about this. First you need to find a proper way to establish the profile and height and rake of the stem of the Vasa, by examining the whole structure including the way the stem is attached to the keel.
Finally, I promised to give an argumentation why I think van Yk gives the height and rake of the inner profile of the stem for the 172 feet ship in his book. I can’t be too extensive here but there are two arguments. The first and most important argument depends on the way van Yk constructs the total length of the ship. As mentioned earlier he uses four measurements to do this: the width of the stem at the top, the rake of the stem, the length of the keel and the rake of the sternpost. In the certer for this 172 feet ship these measurements are given.
If you add the width of the stem, rakes and the length of the keel this adds up to 49,54 meter, 0,85 meter more than the given total length of the ship. This is due to the fact the rake of the stem is not measured from the face end of the keel but from a point behind this face end. I can’t explain this in more detail here, but I suspect this is the case with the Vasa too. The other argument is the fact van Yk gives a peculiar measurement: the length of the stem measured alongside the curve. You would expect this measurement to be measured along the backside of the stem but this is not the case. It is the length of the chord as presented as the line AC in one of the former posts. So it is not the length of the actual curve. Since this is all presented from the upside of the keel this must have been measured at the inside of the stem. This will conclude my contribution to this forum for now. I am curious if there will be some comments on this and what these will say.