Creating a 3D Hull Model

In my first post I talked about the lack of any available blue prints for the Zodiac. Our ultimate goal is to reproduce them by creating a 3D CAD model of the entire boat. The most complex part from a CAD modeling perspective is the boats hull. It is mathematically a very complex surface but optically has very smooth lines and a nice flow to it. And most of the hull you can’t see because it is under water and that is a good thing because that is what keeps the boat afloat.

zodiac full side profilezodiac interiorlayout

To get an accurate model of the hull we will do a 3D hull laser scan when the Zodiac is in dry dock in March 2013. But I wanted to get a head start and create an approximated 3D hull CAD model which I can then use to 3D print little hull models. So I started to look for pictures of the Zodiac from which I can trace some rough lines of the hull above water and approximate lines under water based on pictures from the hull in dry dock. I found a nice side shot from the zodiac and a rough interior layout plan from the website which I loaded into the CAD system and placed them in the proper planes. In the CAD system I created some very basic dimensions of the boat which is 127′ long and 26′ wide and draws about 16′ below the waterline.  Then I scaled the pictures inside the CAD system until the hull measured from bow to stern 127′ which is the known LOA today. The picture below shows the initial setup in MOI3d.

creating the hull - step 1

I could now trace the visible hull lines along the picture and approximate the lines under water based on a few dry dock pictures. After that I have 2 three dimensional curves (B-splines) inside the CAD model which now allows me to loft the hull. The following 2 pictures show that result.

creating the hull - step 2

creating the hull - step 3 - Basic Hull Lofted

As you can see the result isn’t all that useful yet because the lofting function just didn’t have enough data based on the 2 curves to create a hull. At this point I remembered that I saw some hull lines of the Zodiac which were created a few years back. I took some pictures of these hull lines and used the same technique as above arranging each view and scaling the pictures to match the dimensions. Then I started tracing the hull lines and arranged them in the proper 3D position.

This process was actually quite time consuming  since it required a high decree of accuracy and I tried various methods for creating the B-splines. I remembered that using fewer control points on the B-splines will make the lofting easier and the resulting surface smoother. So for each hull curve I tried to use no more than 5 control points and dragged the control points until the curve matched the line in the picture. The tricky part here is do the lines in the correct sequence or you will get lost with all these lines.

creating the hull - step 3 - Detailed Hull Lines

This step is the most important one in this process because the CAD software will use these lines to loft the hull. Now with today’s tools such as CAD software you can create and design such a complex surface in a couple of days. Now imagine the type of effort that was necessary to create a complex hull such as the Zodiac’s 100 years ago when the schooner was actually build. They didn’t have computers or even calculators so creating actual drawings must have taken weeks if not month. Naval architects used scaled wood models which they shaped with a lot of elbow crease, chisels and sandpaper, until they had the shape they wanted. Then they cut the solid models into sections at set intervals which produced the actual hull lines they now could trace onto paper. After that they used mechanical tracing tools to scale the lines.

I was able to re-create the hull in the CAD system in a few days but that includes a lot of learning time and trying different methods. Now all of this you only have to do for one side of the hull because you can later mirror the one side to create a full hull. The next pictures show the selected (yellow) hull lines and the lofted hull as a result. The software provides a few options to play with to improve the result by basically reducing the constraints for the surface. It basically makes a loose fit which makes a smoother surface. It is like the computers version of elbow crease for all you non engineers.

creating the hull - step 5 - Lines Lofted

At this point we have a pretty good approximation of the hull but we  have a lot more details to take care of. We need to close up the stern and then thicken the actual hull surface because the wooden planks of the hull  are probably about 3″ thick. Then we mirror the hull to get a complete hull model. Next is to add the keel beam and rudder. Here is the result after all of that design work.

creating the hull - step 6 - Thickened Hull with Rudder

closeupofnewframes

Once you have the hull model you can now start building the actual skeleton of the ship which is what traditional boat builders started with. In modern CAD systems is now fairly simple to create the curved ribs because you have an exact hull you now can slice in sections and project the precise curves needed for the ribs. The following picture which shows a small section of the ribs I took from the Zodiacs website. I used that photo to get some basic dimensions for the width and thickness of each rib and the spacing between them. In this picture I believe we see a port side section that has been replaced as built by 6”x6”double sawn futtocks on 24” centers.

In the next post I’ll continue with building out the skeleton of the ship and show you the results of my 3D prints. So stay tuned.

Advertisements

3D Printer Arrived

3D Printing Setup

A few weeks ago my new 3D printer arrived and after unpacking, initial setup and table calibration I was printing my first part, a ball bearing. It took me just 30 minutes to start printing. I was fascinated and glued to the printer watching how the plastic got extruded out of the nozzle and the bead was laid down by the  extrusion heads motion. It was just like when I was in college 25 years ago and I watched a fully automated CNC machine mill a part out of a solid piece of metal. Just this time it was the opposite. The material wasn’t removed but added layer by layer. And the machine doing it costs less than $1,000 compared to the $500,000 prize tag for a basic CNC mill. Now the computer technology at its core is pretty much the same. You have a 3D CAD model that gets converted into machine instructions to move from A to B to C in rapid succession which in turn get converted by the software into stepper motor signals which move the table and extrusion head very quickly but highly accurately (less the 0.2 millimeters).

Now the amazing part about 3D printing is that you can print mechanically functioning parts in one path. A great example is a ball bearing which takes shape below.

3D printing about half way done almost there you can see the balls half way printed

After printing is completed you just remove the base which contains the printed part. The plastic material, in this case ABS, is added layer by layer so the process is actually very slow. Printing the bearing took a couple of hours to complete. Once done all you have to do is remove the part from the base and remove any excess plastic or support structure that was added automatically by the printing software. I explain that a bit more in a later post.

the bearing on the printing base the bearing removed from the base

The only thing left to do is loosening the balls inside the bearing and you have a mechanically fully functional part. So now I was hooked and was looking for what to print next. On the web I found various sites were people share CAD models and I started to hunt for the obvious…a case for my iPhone 5…which there are quite a few. So I downloaded some case models and started to print only to learn that most of these were  not optimized for a extrusion based printer or were printed on some high end machine. The results were disappointing. It was pretty clear that the problem are the CAD models that needed to be modified and fine tuned. I spend a lot of time with CAD systems such as CATIA in college and more recently played around with modern versions such as Alibre and MOI3D. I especially like MOI3d for its excellent UI and easy to use capabilities to generate complex NURBS based surface models. But easy to use for CAD software means advanced Photoshop skills times ten.

Try to play with Sketchup from Google which is supposed to be the most easiest to use CAD software and you will understand what I mean. CAD 3D modelling software does require you to put in some time (more than 10-20 hours) to learn how to use it and to actually create something a bit more complex than a cube, cylinder or torus.

But back to my iPhone case project which was next. I realized that I actually don’t need a case because I already had a good one made out of some flexible material. That material is the next problem with cheap 3D printers which just lets you print with ABS and PLA plastic which both is not flexible at all. So I decided I will not design a case but design a replacement cradle for my phone in the car. The one I had just didn’t work well but I wanted to reuse the actual suction based windshield mount that allowed the cradle to be rotated and removed.

So I first started with the actual connector of the cradle to the suction cup mount. The small green part I designed and after two iterations fit perfectly. The reason for just the connector was just printing time. This small part printed in 15 minutes.

2013-02-13 21.21.52

Next up was creating a cradle based on a iPhone 5 model I downloaded from the web. As you can see in the picture below it was a disaster. The wall thickness was just to thin and the sidewalls just broke off when I removed it from the base.

2013-02-13 21.22.22 2013-02-13 21.22.14

So I modified the CAD model and added thicker walls but also removed some more material since I didn’t need a solid base and printing time is an issue.

2013-02-13 21.22.31 2013-02-13 21.22.52

The result was pretty clunky and the iPhone fit but not with its case. So I had to adjust the geometry to add more distance between the sidewalls. And I figured I can remove some more material because I don’t need the iPhone to be fully encased to have it sit on the cradle. I also didn’t like the color so I switched to black.

2013-02-13 21.23.01

Now the next version looked a lot better but still had some structural issues on the corners. The sidewall became loose after I inserted the phone a few time because of the pressure the phone put on the walls. So I had to further adjust the geometry to add some pitch to the walls and I thickened the corners of the wall.

2013-02-13 21.23.37 2013-02-13 21.23.50

Now this version fit the iPhone perfectly but it still took almost 3 hours to print. And I still didn’t like the design to much. It used to much material and felt clunky. So now I looked at the part and examined from all angles to see how the phone was actually supported. I realized I only need contact points at 4 corners so I changed the design again but kept the basic geometry for the contact surfaces of the phone.  If I have some more time I might re-evaluate the 4 point contact decision because you can also do it with a 3 point design I believe. But in any case that is now much better look and it prints in 90 minutes.

2013-02-13 21.24.08 2013-02-13 21.24.48

The small part above is a retainer arm which attaches to the cradle and can be swung over to make sure the phone doesn’t slide out when moved horizontally.  But after putting the phone in the cradle the friction between the iPhone case and the cradle was enough to keep it inside so I didn’t continue with the arresting arm.

Here is the final result which I now use in my car everyday and it works like a charm.

2013-02-13 21.28.37 2013-02-13 21.28.27

So total printing time for all the different versions was about 15-18 hours mostly done after I went to bed in the evening. And I worked on the CAD model another 3-6 hours total still learning more design tricks.  Within 4 evenings I had a fully functional cradle which I now shared on one of the CAD model sharing sites.

So go ahead and download the model and modify it or just print it.

Now most of you Zodiac fans wonder why I’m talking about all of this. Well there is a learning curve involved before you can design a complex boat hull. But my next post will address exactly that and you’ll see how I created a CAD model of the Zodiac’s hull based on pictures in the early versions and later based on pictures from hull lines I found on the boat. And how I then printed various version of the hull on the 3D printer. So stay tuned.

How did all of this get started?

It all started with my first trip on the Schooner Zodiac as a passenger for the Fathers day cruise in 2012. I simply fell in love with this almost 90 year old tall ship which is 167 feet long and beautifully restored and maintained. My two daughters, Katarina and Hanna, fell in love with the Zodiac as well and we simply had a blast helping to sail this big all wood boat. And yes it takes about 20 people just to raise the 2 ton main sail. The boom alone weighs about one ton and there are no electric winches or other convenience features or machines. Its all muscle power amplified by massive blocks and tackle. I was so excited on the first day to raise the main sail that I volunteered to set the pace on the main halyard. Boy, I wasn’t prepared for the instant full body work out and after about 3-4 minutes had to ask for relieve so I could lay down and catch my breath. Nobody told me that sailing a tall ship is hard physical work.

We spend 4 days cruising around the San Juan Islands and had a few times some pretty good wind. Now I sailed quite a bit on modern yachts from 40-52 feet but the size of the sails on the schooner and its size (~200 tons) feels very different. Everything happens a lot slower but when it happens you can almost feel the massive power and force the sails generate. You can hear the boat squeak and crack, see the tension when the ropes stretch and feel the boat slowly picking up speed purely powered by the wind. Its just an awesome display on how to convert the winds energy to propel a very large ship through the water.

So after 4 days on the boat my girls started asking when are we coming back. Well, a few month later in August the Zodiac’s first mate Chris called me one day asking if I want to go to Desolation Sound with them. I was confused and asked “are you looking for more passengers?”. To my surprise the response was “No, No, No we want you to come as part of our volunteer crew”. But the catch was I had to leave on the 12 day trip in less than 3 days. So I got busy quickly and told my boss I have to take an immediate unplanned break from work which he wasn’t happy about but ultimately agreed to.

Three days later I reported for duty on the Schooner Zodiac, met the crew and got busy getting the boat ready for passengers. Now I had to remember everything I learned on the first trip and figure out how to teach passengers not to get their fingers drawn into the pin when working the ropes. It did help that I do have a fair amount of sailing experience skippering bare boat charters but sailing a tall ship is just different. But after a few days and a few minor mistakes I got the hang of it and just enjoyed this experience.

Being a technology geek of course I couldn’t go without a couple of gadgets. My iPhone was loaded prior to the trip with a marine navigation app with updated charts, a tides and current app, and my favorite an app called Ship Finder which lets you point the iPhone towards any commercial vessel. The app then tells you the name, size, destination, current curse and speed over ground, where it is registered and what it transports. Oh yes, and how far away it is from you. The crazy thing is you don’t even have to actually see the vessel. It will plot it on a chart in reference to your own current position. So over the next few days people keep asking me questions about where we are, how fast are we going, what is the tide situation, and yes what’s the name of this large container ship out there. And my response always was “well, there is an app for that”. Even the captain started to notice jokingly that I seemed to have an app for everything. Well, a few hours later we crossed commercial traffic lanes  and two large vessels came towards us. I could see the captain and first mate getting busy trying to figure out if we will be getting to close soon. So I just casually mentioned the name, course speed and distance for each vessel after a brief look at my app. But I also added that this data might be 10-20 minutes old and should not be used for navigational purposes. We are a passenger vessel after all and the rules are pretty strict. Captain Tim’s look was disbelief because usually he is always 20-30 minutes ahead of everybody else on the boat.  In any case to make a long story short “there is an app for that” became a standing phrase on the Zodiac.

During this trip I learned from the crew that there are no blueprints or plans for the Zodiac. The initial set burned in a fire in the boat yard that build the schooner. A few years later the remaining set of plans got lost when the marine architects offices burned to the ground. The only plans that exist are a set of hull lines which were created many years ago using manual templates when the schooner was in dry dock. These plans were needed to pass the basic Coast Guard stability certification which is necessary to transport passengers. These plans also assume a symmetrical hull which is most likely not the case as Captain Tim explained. The Zodiac was used for 40 years in San Francisco bay as a pilot boat bringing pilots to large vessels way outside the Golden Gate bridge. To transfer the pilot the Zodiac had to come alongside the vessel under any weather and wave conditions and that often caused the Schooners port side to slam into the much larger cargo ships. During restoration of the Zodiac the crew discovered that the port side hull structure had far more signs of wear and tear and even additional bracing that was not present on the starboard side. Captain Tim also noticed slightly different sailing performance and behavior on a port or starboard tack which could be explained by a non symmetrical hull. But nobody really knows which is what intrigued me. I asked Tim if he considered a hull scan when the Zodiac is in dry dock and he said yes but he simply can’t afford it.

This is were coincidence and proper alignment of the stars come into play. It turns out one of our passengers on the Desolation Sound cruise, Ross from Toronto Canada, is a 3D scanning engineer who usually scans parts for quality control purposes. So we started talking about how we can make this happen. What equipment do we need, how can we conduct the scan within the tight quarters of a dry dock, and how do we process the massive amount of data generated by such a hull scan. And most important, how can we do this on a minimum budget. So by the end of the cruise Ross and I had a plan to do a hull scan when the Zodiac is in dry dock in March 2013. Ross will handle all the scanning and data acquisition and I would finally put my German engineering degree to work to figure out how to process and align the point cloud data and how to turn that into a hull surface model that we can then analyze and use for a full CAD model of the Zodiac.

Up next, I got my hands on a 3D printer and a bunch of CAD and point cloud management software.