Creating a Framing Model

It’s been a while since I updated this blog but since I only work on this as I have spare time things just take a little longer. The last blog was all about turning 3D scan data into a surface model of the hull and deck of the vessel which then were used to create 2D hull line drawings and a 2D rigging plan. This blog will outline how I created the basic framing of the vessel using the hull surfaces as a starting point. The actual section frames are not visible except a very short piece above the deck underneath the cap rail. And that piece is only half of the actual section frame width as you will see later in the images.

A few month ago I found a new piece of software called onshape.com which is a fully cloud based CAD system build from scratch over the last 2 years by a bunch of long time CAD experts who used to work on SolidWorks. What is absolutely amazing is that it runs in your browser and you don’t need any beefy hardware since all the processing is done in the cloud. Because of that they also have an iPhone and iPad app with full design capabilities enabling me to crawl around the boat to capture and design details right on site. And it gets even better since the software is free to use for anybody as long as you don’t exceed certain limitations such as storage used and number of CAD models active.  I can now share the model with other volunteers to review the model or even enable them to collaboratively edit the model. So I could be working on the rudder steering mechanism when at the same time someone else would further detail the deck structures. And we both can see each others changes immediately. Think of Google docs for CAD.

Update: Onshape recently published a blog post about this project which you can find here.

I’m now looking for some engineering students and other volunteers who want to learn and improve their CAD skills and help us further detail the 3D model of the vessel. Because of this new software we can now crawl around the vessel take measurements and detail the 3D model on site. So if you want to help let me know by posting a comment.

To start this next phase of the project I imported the hull surfaces into onshape.com.

Schooner Zodiac Hull Surfaces

Schooner Zodiac Hull Surfaces

 

Onshape.com is primarily a Solid Modeler which means parts are represented as solid objects instead of an object shaped by its exterior surfaces (Surface Modeler). The first step was to take the exterior starboard hull surface and thicken it by 3 inches towards the inside since the hull planks are 3 inches thick. At this point I made the decision to create a symmetric hull model based on the starboard hull. If you read the previous post you’ll know that the scanned hull is not symmetrical. The port hull is actually indented by up to 3 inches towards the center plane because of its use as a pilot vessel for 40 years. I simply tried to make modeling a lot simpler by not having to deal with different port and starboard hulls. Once I created the starboard hull as a solid I simply mirrored it on the center plane.

Symmetrical Starboard and Port Hull Solids

Symmetrical Starboard and Port Hull Solids

The next step was to model the transom for which I simply couldn’t use the “thicken the imported surface” approach because the transom also wasn’t symmetrical. So I recreated the transom surface  by sweeping it along curves created by slicing the transom in sections. I extended the transom a little more which will later be cut off once the deck and cap rails are in place.

Now it was time to model the keel based on the outline of the imported keel surfaces. I choose to create the initial keel body by extruding a sketch that roughly mapped to the keel outline. I would trim the keel body later once I start fixing all the transitions between the hull surfaces.

Rough Hull Surfaces with Transom and rough Keel

Rough Hull Surfaces with Transom and rough Keel

Up to this point things went pretty quickly since I just recreated objects based on the imported surface data. But as you can see there are quite a few imperfections in the hull surfaces/solids which I had to fix in the next step. At the bow for example the hull surfaces didn’t touch and there was a gap that needed to be closed. The following three pictures show how that was done.

Screenshot 2015-06-16 14.13.09 Screenshot 2015-06-16 14.14.10 Screenshot 2015-06-16 14.15.30

I also had to trim the keel since it is not of equal width between the stern and the bow.  And I filled a couple of the larger gaps in the stern and punched out the hole for the propeller in the keel. This work was a little bit more tricky since onshape.com doesn’t have a lot of functionality yet to fill gaps between surface solids. This is usually a domain for Surface Modelers but I’m sure onshape.com will add these capabilities overtime which will be time savers. The fact that I could create a fairly smooth and almost “watertight” hull model speaks for the capabilities of onshape.com which was in beta when I used it.  The last item I added in this step was the rudder and rudder steering axle.

Watertight Hull with Rudder

Watertight Hull with Rudder

Up to this point I just recreated and fixed a hull model using imported data as a starting point. It was now time to start creating section frames which are the skeleton of any wooden hull vessel. I know the frames are 12 inches wide and 6 inches deep and are spaced 24 inches on center.  The section frames are actually build out of 6″*6″ pieces of wood that are sawn to the curved shape to follow the hull and are doubled up. A shipwright would refer to this as 6″*6″ double sawn futtocks on 24″ center framing. I choose to model the section frames as single pieces since I was planing to 3D print the model on my little 3D printer and having multiple pieces for each section frame would just cause a lot of problems with print resolution.

The Zodiac is about 127 feet on deck which should result in roughly 60-62 section frames. To create these frames I needed to slice the hull model using 62 planes. This was a bit painful since onshape.com doesn’t have the create multiple planes feature yet. So I had to create each plane with a 24 inch offset manually. The next feature I needed was to use the the 62 planes and intersect them with the hull and keel to create section curves.  This again is a feature that isn’t essential to create a model but helps speed up the time it takes to create one. The support team was super helpful to take my feature requests and I’m looking forward to see it implemented in the future. In the meantime I had to slice the hull into sections one at a time which now created lots of parts (hull fragments) which did have the section curves I needed to create the frames.

Sliced Hull

One of the interesting thing about any old wooden vessels is that there are no straight lines or flat surfaces. Everything is curved and that makes it beautiful to look at but quite difficult to model. No section frame is the same and I had to create 60 sketches based on the section curves created by the slicing of the hull. Each sketch had to be a closed profile that can later be extruded 12″ to form the frames. I also had to extend the sketches on the top by 24 inches since the hull surfaces ended at were the deck would be. The extension was used to later attached the deck walls and the cap rail. It is also interesting to note that section frames are parallel to each other and towards the bow and stern actually punch though the hull surface. During construction over 90 years ago that was fixed with a lot of elbow grease by trimming of the edges of the frame to make it follow the lines of the hull surface.  That is where a good eye came into play as well to make sure all the frames are shaped properly.

Sketches for all Section Frames

The top extension of the section frames is actually only half the width of the frame since it only needs to support the deck walls and cap rail. There is no structural load above the deck on the frames. And the forward frames keep the aft part of the frame and vice versa for the aft frames.  The following picture shows all the frames extruded and trimmed on the top. You’ll notice as further forward or back you go as more of the frames punch through the actual hull surface. In a last step I will trim all the frames but we are not ready yet.

All trimmed Section Frames

Next I added the deck walls by lofting a surface along the edges of the frame extensions. Since I created the hull symmetrically I simply mirrored the deck wall from starboard to port.

Screenshot 2015-06-16 15.39.06

In an earlier step we split the hull into sections so we can create the section curves. At this point we no longer need the hull sections so I merged them back together into a port and starboard hull. That is when you can see some rendering approximation errors. Some of the frames were not visible with the hull sections used to create the frames. But after the hull sections where merged again more frames punched through. The underlying model is still accurate but the rendering and shading approximation could use a little more detail to avoid such “visual flaws”. But again this is really a very advanced scenario and might be not at all that common.

Screenshot 2015-06-16 15.48.57

After that I added the cap rails which cap off the deck walls and section frames.

Screenshot 2015-06-16 15.54.13

At this point we have done most of the hull framing except the transom to which we get later. I created the lower deck surface and moved on to recreate the deck surface. Unfortunately onshape.com doesn’t allow inserting parts into a part studio yet so I had to recreated the deck surface inside the part studio. The deck has a slight arch toward the center plane to ensure water runs off the deck quickly.  The deck itself is 3 inches thick so I created a few sketches to loft it. I made sure the sketches extended beyond the hull solids so I can trim off the excess with a Boolean subtract feature to keep all the surface solids connected water tight.

Screenshot 2015-06-16 15.58.29

 

Now it is time to trim all the frames against the hull and keel and delete any of the trimmed off parts. The final result shows a couple of frames that didn’t trim properly which turned out to be a bug which onshape.com is in the process of fixing.  But the 3D model I was able to create simply based on imported hull surfaces is pretty amazing.

Screenshot 2015-06-16 16.21.20

 

You might ask why I went through the effort to create such a complex model. There are various reasons why this was a great exercise. The primary reason is to be able to create 3D printed models for educational purposes. Once the model was created I could print 60 frames and 5 keel sections on my little UP mini 3D printer and assemble a scale model by simply sticking the frames into the keel. Other reasons are to create a virtual walk through for marketing and education purposes. Or to create models and blueprints for Coast Guard inspections and maybe update our stability analysis so we can fly top sails with passengers on board. And maybe someone wants to create a model kit or ultimately create a replica of the vessel. In the end it is a lot of fun to learn new software on a real and complex project.

2015-04-06 15.20.48

2015-04-06 15.20.18

 

What’s next? Further detailing the framing model by adding deck frames. After that I’ll start detailing the interior by adding state rooms, the galley and various systems such as fuel tanks, fresh and waste water tanks, bilge pump locations, prop shaft, masts and deck structures. But what I really hope to do is inspire some student or high schoolers or other volunteers to come out and pick a section of the vessel and help further detail the model. In the end all products we use today started in some 3D CAD model and as more young people get excited about CAD as better and more innovative products will be designed in the future.

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One comment

  1. Great stuff Chris! I had a big pleasure reading your report. Fundamentally men are kids: they focus their passion and energy without any apparent reason or goal, just to discover after a while that yes, there are plenty of good reasons and even commercial opportunities out of it!
    Take care
    Roberto


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