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HMS Pandora (1779) CAD build log

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This is my CAD build log for HMS Pandora.  I am using the free version of Sketchup (with a few add-ons) to construct the digital model.


My primary reference is Anatomy of the Ship: The 24-gun Frigate Pandora (McKay).  I'm also using a number of build logs here on MSW, especially HMS Vulture (Dan Vadas) and HMS Kingfisher (Remcohe).  While the Swan-class builds are slightly smaller, I am assuming (a very dangerous proposition) that similar building techniques would have been used, since they date from the same decade as Pandora.


I'll use this post to show the current state of the project, and add updates to further posts.


Edited by SketchupModeller
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Google Sketchup is a free drawing application (at least I think it's still free). You should be able to search for it.


Question for others-has anybody had a problem with Sketchup crashing their computer? I downloaded it about 4-5 months ago, and could not use my computer until I took it off. I've got TurboCad V18, so I don't need Sketchup, but I'm always interested in other CAD programs.





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Part 1: Importing, Scaling, Levelling and Positioning Plans


Since there seems to be some interest in 3D modelling, I'm going to try and include as much detail, including pictures, as I can.


The first step in any build, be it wood, digital, scale, or full-size, is preparing the plans.  Scans of the sheer plan and outboard profile were combined in PicsBuilder Studio, a basic (and free) image editing program.  This creates a single plan with most of the details not seen on the sheer plan but that will be needed to construct the hull (wales, gunports, channels, etc).  Because Sketchup will reduce large images to 3000x3000 pixels, I divided the combined plans image into two halves (approx 2800x2800 pixels each) and imported them separately into Sketchup.


Anatomy of the Ship: Pandora includes the body and lines plans on the same pages as the sheer plan. If this was not the case, they would have to be imported separately using the same method.


Once in Sketchup, I scaled the plans to full size using the longest available dimension for greatest accuracy.  Before and after pictures for this are shown below (the marked length should be 120')




Next, the plans were rotated so that the sheer plan was horizontal. This rotation also made the body plan vertical, but the lines plan was now off by a few degrees.  This will be corrected soon.


By "Exploding" the imported images, I drew in lines to separate the individual plans (in Sketchup, lines define the edges of surfaces.  By placing one or more lines on a surface and connecting two edges, the surface is split into separate parts).  At this point, I rotated the lines plan to make the centreline parallel to the sheer plan.  It doesn't matter that the station lines on this plan are not at 90 degrees to the centreline, because I won't be using them.


Finally, I used the centreline and fore perpendicular as guides to move the body plan and sheer plan into position as shown below and drew in the load waterline and perpendiculars.


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    Sorry to hear about what happen. A good amount of stuff when you install them will try and get you to have other stuff install, which is a problem all in it's own. I always say no to everything but what I am installing. I have also run into the same problem as you, but was able to get by it and uninstall the program. I have another drive that I have clone this drive to, and once a month I redo the clone in case I can't do a restore back to another date. It has save me more than once, I am a retire IT enginere and hate to work on my own computer so that is why I cover my butt as much as I can.

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Part 2: Reference Lines


In the previous part, I mentioned that I would be ignoring the station lines drawn on the sheer and lines plans.  This is because the plans helpfully provide the distance between station lines.  If these dimensions were not listed, I would have to go by what the lines on the drawings, which would not be as precise.  Starting from the fore perpendicular, which I have arbitrarily decided to use as a reference point, I marked off the specified distances and drew in the station lines on both the lines and sheer plans.


The lines highlited in red on the picture below are the ones drawn in.  Note that they do not line up with the lines on the plan (black).  Also note how the plans are somewhat blurry.  Some of that is due to the scan, and some is an artifact introduced when exporting the image from Sketchup.



Next, I drew a line following the bottom of the keel, transferred it over to where the model will be built (red arrow), and marked it with the stations (green arrows).  This line will become especially important when building up the shape of the hull later on.



The next post will cover setting up the keel and what to do when plans don't agree with each other.

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Just to add to the chorus of praise, I'm delighted you're doing this log in such a detailed way. It really shows how much cross-fertilisation there is between the types of build, and that there are in fact so many different ways to build a ship. I'll be following this one right through to the end.


Great stuff!



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Part 3: Masts and Yards


I had planned that in this update I would start describing how to build the keel.  However, things don't always go according to plan.


To this point, I've been reconstructing the earlier steps of this build so that the log will describe the entire process of digitally creating the model.  This is a rather tedious process that doesn't seem to make any forward progress, so as a break from the tedium I've started drawing up the masts.


McKay's plans for Pandora's masts and yardss include all the necessary dimensions, so I modelled these parts using the written dimensions, instead of taking measurements off the drawings.  As a bonus, this is much more accurate (and less frustrating) than measuring off of drawings.


So far, I've completed most of the mizzenmast (seen below, with first few parts of the mainmast) and mainyard.  Some parts, such as the trees and bibbs, still need to be rounded off, and a number of details (sheaves, eyebolts, holes, and the like) still need to be fitted.



As a quick test, I textured some of the spars and rendered them using Kerkythea (a program that's frequently used to render Sketchup models).  I'm probably going to use a different wood texture for the final renderings, but I'm otherwise happy with the overall appearance.  Below are pictures of the yardarm as it appeared in Sketchup and after rendering.




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The studdingsail boom (smaller diameter yard in the pictures) would be slid inward when the studdingsails were not being used.  The white objects are the boom irons, and as the name suggests, would have been made out of iron.  Per AotS Pandora, the outer (boom) iron would have a roller for the boom, and the inner (quarter) iron would be made of two halves that could be unhinged, very much like the piece of metal that holds a gun's trunnion in place (neither the roller nor the hinge has yet been added to the model). 


From the studdingsail boom would be hung the studdingsail yard (not shown in the post above), from which would be hung the sail.  I presume that the yard and sail would be taken down to the deck when not in use.

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This is really awesome.

Finally found someone that also using SketchUp and Kerkythea too  :D 

I thought I know you from somewhere with this so advanced skill with SketchUp and ship modelling.
Perhaps in SketchUcation or somewhere else.

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Part 4: Keel Parts and Keel Errors?


Now that the plans and reference lines are in place, I can start drawing in the ship.  My approach, unline ppddry's, is to convert as much as possible directly from the source drawings to the 3D model without a complete 2D CAD step.  I may revisit this approach.


I started the keel assembly by importing and scaling McKay's drawing of the keel (drawing B2 in AotS Pandora).  This was traced and aligned with the plans on my work surface, as shown below.  As a note, the lines between the keel and the keelson mark the edges of the frames



But there's a problem: looking at the next picture, we see a six inch difference (red line) betweehn where the foremost part is and where the body plan says it should be.  What happened?



On other error, illustrated by the green line, is a four inch difference between the plan's fore perpendicular and the line drawn from the fore perpendicular at the bottom of the plan (i.e. the line I use as the fore perpendicular).  This suggests to me that the scanned plan is skewed slightly to the left, and thus not completely accurate (the horizontal lines on the plan are actually horizontal).  For this reason, I will consider the traced keel to be correct.


Having decided that my work to this point was not completely wrong, I brought the keel to the centreline and extruded most parts to the full thickness of the keel.  A few parts, specifically the sternpost, aftmost piece of the keel proper, and some of the stem pieces, were tapered in accordance with McKay's drawings.  The rest of the shaping, including cutting the rabbet, will be done later.



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I have a 3d program that works in Vista wth no problem and its free to down load! its called DoubleCad XT




down load from this site


I have an earlier version but this should work on your computers with out freezing it up.


Has anyone contacted Google about your problems with SketchUp?

Edited by the learner
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Part 5: Tracing and Placing the Station Profiles


This update will cover the process of tracing and positioning the profile of each station, in preparation for creating the first surface that will define Pandora's 3D shape.  As a note, the portion of the ship aft of the last station will be dealt with by a different method, which will be discussed a bit later.


As can be seen below on the body plan, the stations are aligned at the top of the keel (green line).  Since the keel is not horizontal on the ship, the waterlines follow a curve - note how waterline W touches the centreline at two points (red arrows).  As  result, it is much easier to use the keel as the reference line.



After all unnecessary parts of the keel assembly were hidden, a centreline (green line in the picture below) was drawn on top of the keel and marked at each station (red arrows).  This was done for the entire length of the keel.



At this point, I can start tracing the profile of each station. Here, I'm using station 13 as an example.  Starting at the reference line, I mark the vertical centreline every 12 inches (green lines), and draw a line laterally (purple lines) to the station line.  Once this has been done for the entire station, it's a simple matter of connecting the dots (blue lines).  Because the lines I'm tracing here represent the inside edge of the planking/outside edge of the frames, they will also form part of the rabbet.  Taking this into account, the lowest line was connected to the keel a few inches in from the edge (red circle).  The final profile is composed of at least 25 segments, reasonably approximating a smooth curve, although there were a few areas where it was necessary to add extra points.  Given the fuzziness of the scanned lines, I only measured to the nearest 1/4 inch.



Once this was done, the horizontal lines were erased and the final shape was copy/pasted into position on the points previously marked on the centreline of the keel.  When every station had been completed, the model looks like this.



The next few posts will define the stern portion of the ship and convert the lines shown here into a surface.

Edited by SketchupModeller
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This is really excellent! I'd asked on another thread for a step-by-step practicum on 3D CAD ship modelling and had forgotten that this thread is exactly that!


Thanks so much for taking the time to do this. I'm now looking forward to the conversion to surfaces as I've been struggling with that. I've also been struggling with the stern of my longboat as the body plan didn't show all the stations so I'm trying to compute the shape of the frames from waterlines -- but so far failing.



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  • 2 weeks later...

Kudos to you. Fantastic Work.

I was using Wayne’s tutorial to draft of ship’s plans in 2D. Then I realised that the latter part of the drafting could be done in 3D which could be used to fair out and remove any “bumps” from the resulting curves, thus producing smooth curves for the final plan.


Your build gives me the idea that the initial stage of drafting in 2D is unnecessary and it could be done straight away in 3D. Your finding flaws between the lines in the AOTS drawing and your build bears this out- that it is possible.


What I’d like to know is- Can a final set of usable plans be drafted using Sketchup? I’m asking this because I always thought that Sketchup had problems dealing with curves especially Splines. Secondly Sketchup had a problem in scaling and printing plans.


I was told that the best solution would be to draft plans in 2D, export them into a 3D application. Extrude and render them in 3D, correct the flaws and then reuse the CAD program to loft the final set of plans.


Aah the tedium of this!!! Now you’re holding out hope for some long suffering and aging modelers like myself.


By the way my surfing on the web seeking answers to the above led me to believe that Rino was the only app capable of doing what you are doing with Sketchup. Shows how the web could be so misleading.


Do you intend your build to be only a virtual model? Whatever the intention keep up the good work.


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It is apparently possible to produce usable 2D drafts in Sketchup.  Since I expect this will only be a virtual model, I haven't really looked into this much.  Google is probably the easiest way to figure out how to print to scale, but this site seems to be helpful: https://sites.google.com/site/sketchupsage/master/geo/print-to-scale


The issue of curves is a different matter entirely.  You are correct in that Sketchup doesn't handle curves well - or at all.  Curves are treated as a set of straight lines that approximate the true curves, and spline and lofting tools are only available as downloadable plugins (and these will also only generate a series of straight lines).  This leads to a few problems.  First, the tools used to interpolate between curved lines are not entirely reliable, as will be seen in the next installation of my log.


Second, as more lines are used to define a curve, the file size gets larger, and Sketchup slows down a bit (especially on older computers).  Because of this, I've simplified the curves somewhat more than I would if I was building the model out of wood.


The third problem becomes apparent if you try to take a section of a lofted surface - the section will have a slightly jagged edge to it.  This is because the curved surface is approximated by a number of triangles lying at slight angles to each other.  I'm not sure how much of an impact this would have on the final model, but it does bring into question the accuracy of that section.


The last issue is likely more of a user problem on my part, but I haven't yet found a decent method of drawing in the inside edges of frames accurately.  There is a simplified workaround I've been using, but it likely isn't accurate enough for someone looking to draw plans for a POF build


My opinion is that Sketchup would work quite well for designing a POB build where the bulkheads are aligned with the stations, but may not do so well at drawing every frame of a POF model.


One other point to bear in mind is that Sketchup is very labour-intensive for this sort of work; I've had to draw in or redraw almost every line individually.  I don't know if other programs are more efficient, but I expect there must be something better (and likely much pricier).

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Use this website for downloading this amazing program


I have many years of usage of the program, but I have paid for mine in order to resolve the issue of resolution and printing.

I got this program in 2000 when it was first released by @Last Software this for house design and drafting, very simple and with short learning curve.


But back to this amazing ship, very nice the way you are "building" the ship!

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SketchupModeler, gee thanks --- I'm a little disappointed that i have to still keep looking for the Holy Grail, ie a cheap program which can do everything including scratching your back!

Nonetheless I'll still keep watching your build with interest as it is fascinating, Maybe it'll throw light on what I want.

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