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HMS Leopard 1790 drafting CAD plans, designing model project


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Ok, at first I was hoping to take part on the group build HMS Triton, but as my intention was to copy the complete design into my computer to make my own CNC cut parts, I was turned down by the admins due to copyright concerns. As an ex kit manufacturer myself I fully understand their views, although I think that home designed CAD kits/models are a way of the future that will soon take up a much bigger part in the modelling world.

 

After that failed attempt, I tossed around a few ideas for a while and stumbled over Rif Winfield's The 50-Gun Ship on that famous internet auction house, which was quickly purchased. The 74 is the secret love of my life especially the Bellona, but as a first ship building project I thought I might be biting off more than I can chew with something of that complexity. I have been building models all my life, mainly airplanes with a lot of plastic and a nice number of scratch built flying scale models and a few cars, but now, It's time for something new - a sailing ship.

 

Winfield's book has some very nicely done drawings, what the aircraft guys would call three views, done by a Mr. John McKay in 1997. I scanned part of them and imported them into my CAD programme (for my own use!). As an architect I use one of the most popular german CAD programmes at work, designed especially for architecture called Nemetschek, which is what I will use for my Leopard project. The eagle eyes here will notice that I'm using the dated 2004 version as that's the one I've got. I'm calling this a project as I don't know if I'll ever finish it, so please consider this more an ongoing learning process than a build log.

 

I started off with the Outboard Profile. It was scaled up to full size in the CAD programme and the whales were traced on a new layer by using circular segments and here the first problems popped up. From an engineers standpoint, I was expecting the whales to be of a full circular segment but they turned consist of several, at least two, each with a different radius. For now I decided to stick to McKays profile.

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Edited by CTDavies
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I'm going to have to work out how to embed images into the text. Bear with me, I'll get there eventually.

 

Next thing I noticed was the wales, strakes and rails aren't always parallel. Aftwards of the dead flat they are, but towards the bow they run closer to each other. At first I thought this might be a scanning inaccuracy but McKay's Profile is cearly the same and several of the models in Winfield's book also have this feature. Again I decided to stick to McKay's Profile.

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I am a big fan of Harold M Hahn's Ships of the American Revolution and decided, to keep this design fairly straightforward, to adopt his way of framing using his double and single thickness method as used on his HMS Alfred design. While working on this I found, to my genuine surprise that this corresponds with the short vertical lines under the keel that are obviously Room and Space indicators. Some gun ports had to be shifted slightly.

 

 

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Hi Wacko, thanks for tuning in.

 

The next shot is a close up. According to my CAD programme the distance between the Room and Space indicators (as I call them) is exactly 5' 6-1/2". Could that be right? I have basically no idea on sailing ship designs so I'm going to have to rely a lot on your generous help here. Of course I could try and locate some of those historic books on ship designs and dive into them for a year before I start on this, but that wouldn't be much fun, would it? I do have Avery's double set on Ships of the Line and the first volume has a lot on designing, so I'll be reading that one a lot in the next few weeks. Here's that close up:

 

 

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There was a slight difference of frame thicknesses about where the steps are on the hull, just aft of the dead flat. I solved this my own way by omitting the double thickness frames here next to the gun ports and increasing the single frames to 1' 3". This turned out to be a very tidy solution and I was very pleased about that. I have not made a decision yet on what scale my project will eventually be. At the moment I am designing my Leopard full size, which is one of the advantages using CAD programmes. I did print out a side view, sorry, the Outboard Profile in 1/36th and 1/48th scale, but, boy, those scales would make a BIG model. For now I'm comfortable working full size.

 

 

post-4343-0-26956000-1392935944_thumb.jpg

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The top centre gun port here is not located exactly between the two single thickness frames here (you have to look closely and you'll see what I mean). I changed its position. Actually I went through all gun ports and moved them around just a tad to put them right where I think they need to be. This was the first deviation from McKay's Profile. Would you have done the same? I'm assuming this is a typical inaccuracy you would find on ink drawings.

 

 

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  • 2 weeks later...

Hello Chris, it's always good to see another CAD project around here.

 

I agree with Russ's comment that frame timbers would be shifted to fit the ports.

 

Also, the Hahn style of building includes a significant simplification that would interfere with frames lining up with gunports.  Hahn made his frames the same thickness for their whole length, while in real life the frames would be thicker at the keel and reducing in thickness (in the fore and aft direction) towards their upper ends.  For example, a frame might have been 1'-3" at the keel and reduced to 1' or less at the topsides.  As a result, even if frames did not have to be shifted, it is unlikely that gunports that did lie between frames in real life would correctly lie between Hahn's frames.

 

Because of this, I would not automatically ascribe differences between the sides of the gunports and frames, especially Hahn method frames, to inaccuracy in the original drawings.  A better check for accuracy might be to compare the distance between each pair of gunports - this should be the same for every pair (although some might be different to fit around entry steps, etc.)

 

Hopefully this will help.

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Once you start shifting ports around, you will run into other problems later, such as chains getting in the way. Russ is absolutely correct in stating that the top timbers were shifted to accommodate the ports. They were located where they are by the original designer for a reason!

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