Model of Hunter 28.5 Sailboat. I Made It at TechShop

This instructable is going to describe the process of 3D modelling and then building a semi scale model of a Hunter 28.5 sailboat.  I own the full scale boat in the pictures which is why I am choosing this as the subject.  The model will be  a 1/10 scale model for radio control. The full scale boat is 28.5 feet long so the model will be 34.2 inches long.

http://www.techshop.ws

First step to making a model is finding an image of the side and top view of the boat.  This will be used to sketch on inside Autodesk Inventor.  The 2 photos do not need to start out at the same scale.  You can adjust them after adding them in CAD.

Create a sketch and insert the side view image.  Draw a few lines with known dimensions.  In this picture I drew lines for the overall length of the hull which in scale is 34.1 inches.  The draft of the boat is 6.26 inches in scale. I imported the image and then enlarged it so that the image is aligned over the overall length line and the the draft line.  

Next, add the top view in the same manner.  On a perpendicular axis to the side view, create another sketch and insert the top view.  Use your overall length guideline you made on the other view and create a box using the beam dimension to position the image.

Next I sketched the overall outline of the hull onto the side view.  I did this basically by tracing the outline with spline curves for the hull and straight lines for the keel.

Sketch some outlines to the top view.  Create the overall hull shape this way.

Create a section for the transom.  Create a work plane at the angle of the transom.  Then sketch the transom outline by looking straight down at the section.  You can trace by looking through the tilted workplane at the section.  I could not get Inventor to project the transom sketch onto the workplane in any manner other then normal to the plane which put it too far rearward.  I had to make new splines for the transom overlayed over the original transom sketch.

Create a workplane that is along the bow and sketch a profile section for the bow.  I find it easier to loft it the bow ends at a section instead of a line representing the front.  The bow on this boat has about a 4 inch blunt shape with radius corners on the full scale version.

Make cross sections to loft out the hull shape.  Use the top and side views to draw in about where things should go.  Make everything construction lines except what you want in the cross sections.  If you don't, when you loft it will do weird things and you'll go back hunting through sketches looking for non-construction lines to turn into construction lines.

Next create the loft from the cross sections.  This is where you'll find out if you forgot to turn any lines on the sections into cross sections.  If you go from one part of the loft to the next and it twists or does something weird, it's probably because an extra line is not construction and it's trying to transition into it from the prior section.  If everything goes smoothly you'll get something nice looking.  After you see the loft you may have to go back and edit individual sections if the loft isn't smooth and you've got a bulge somewhere you shouldn't. I had to edit the second to rear most section several times to get it to transition into the transom curve decently.

Use the patch surface to create the deck surface and transom surface.  On the real boat the deck has a couple of degrees crown on it.  I will redo the deck after creating the cabin and then I'll have intersecting surfaces/solids I can join.  You may have to switch a few lines from construction to regular to get the surface command to pick up the edges down the center line of the boat.

Sketch a few sections for the cabin top by projecting some lines from the drawing and also using project cut surfaces so you can draw the sections off the deck surface as it is right now.

Loft the cabin top surface from the sections you created. I just have a single line as the front section so it comes to a point. I created 3D splies down the corners and bottom edge.

I decided I wanted some crown on the deck.  I supressed the existing deck feature so I could make a second go at it without redoing the cabin top.  To start with I sketched a loft line across the transom.  Then I created a couple of new workplanes and sections to add curve to the cabin top. I tried lofting it at once but couldn't get it to use the deck edge as a rail for the loft and get it to follow that edge.  So I want back and just did a loft of the fillet inward.  

Next I made a patch surface to go from the loft I just made to the edge of the deck.  I set tangency from the new patch to the loft I just made so it will be a smooth surface.

I sketched on the back edge of the cabin and added enough lines to be able to make a surface patch to make the back surface of the cabin.  Then made a patch surface.

I sketched on the back edge of the cabin and on the rear transom edge to make 2 sections to loft the cockpit coaming.   I made the section extend down below the deck a little bit.  It didn't carry through into the loft for some reason.

Next I made patch surfaces to fill in the half shape of the hull.  A couple of 3D lines were needed for the missing edge on the bow and transom surfaces.  Then I stitched the surfaces and created essentially a half hull solid.  I did the same thing for the cabin top and cockpit coaming.   When I finished this I had 3 separate solids.

Next, I combined all the solids into one big solid.  I had to extend the cockpit coming surface down because it wasn't intersecting the deck surface in a meaningful to inventor manner.  I did that by using the move face command and dropping it 0.1 inch.  At that point I could combine all 3 solids together.  I am going to sketch the keel next and add a few more features to the cockpit area.  I am going to shell the completed solid and leave it open facing the middle.  This time I am going to make the inside structures and sections from just half the hull model.  It will make it easier to visualize the sections without trying to create them inside and enclosed complete hull.

Next I started working on some cockpit detail.  I created a workplane at the forward inside corner of the cockpit coaming and started a sketch. I projected the edge of the coaming and cabin to get an outline for the cockpit.  I created another parallel workplane .4 inches lower since this is roughly where I wanted the top surface of the seats to be.  From here I projected the cockpit outline and extruded it upwards as a cut to remove the material above the seats.

Next I sketched on the seat surface to make the cockpit floor shape.  This has a T-Shaped cockpit with the back portion angled forward.  I did 2 more cut extrusions to make the final floor shape.

Next I started working on the keel shapes.  I first sketched an outine off of the original boat image.  After that I went to work making 3 sections for the 3 profile areas.  I extended the keel lines up into the hull a ways so that I could have a shape to join with the hull.  I didn't want any surfaces of the keel to end below the hull and leave a gap.  

I couldn't get the keel loft to go with all 3 sections at once.  It always had an issue trying to use a rail with that much angle at the middle section.  I made 2 lofts.  The lower half and then the upper half and everything came out pretty smoothly then. 

Next I made the keel a solid by making patch surfaces along the bottom, top and rear edges.  Then stitched everything into a solid.  

Next I joined the solid of the keel to the solid of the hull.  That's pretty much it for modelling the hull.  I could add more detail but it isn't really necessary for building.  The actual boat is more rounded then this.  I plan on just adding some sticks around the corners so sand in smooth corners in the finished model.  I mirrored it just to get a look at it.  No other real reason.  I undid the mirror after taking this screen shot.   I have had no luck trying to shell out the hull surface.  I am thinking of exporting it as line data and importing it back in to lose the history now and just have a solid object to see if that will work.  It's not the end of the world either way.  I can draw internals off sections cuts either way.  I will just need to offset the outer surface cut geometry for every section instead of shelling if I can't get a shell to work one way or another.

In the mean time I have decided I really wanted this to be larger then 34 inches when it's finished.  If I'm going to go through the effort to build it, it won't take any more effort to go a bit bigger.  I took the finished half hull form and I exported it as a .stp file to have the solid with no history.  This is to make things a little easier and to not have to see so many error messages popup every time I update any part of the drawing.  From here on I only need the hull solid to work with.  I will end up bringing the image back in later on and scaling it to match the solid to get the mast locations and draw the rudder.  I used the derive command on the new solid to scale it up to roughly 1/8 scale instead of 1/10 scale.  The finished boat will now be 42 inches instead of 34 inches.

Now I start the task of drawing the first part.  I am making the longitudinal former first.  I am going to make all parts out of 1/8" lite ply for the formers and bulkheads.  In my smaller test project boat, I made some bulkheads out of 1/8" balsa to try and save some weight and had a lot of problems splitting and cracking them during construction.  Lite ply is much more durable without much of a weight penalty.  I tried to keep the spacing for the bulkheads to 2 inches or less.  More then 2 inches seems to make strip planking a much more difficult task.  The more bulkheads there are, the more glue spots you get to hold everything in place and keep the curves you want.  This part took several hours to draw and I think it's finished now.  

It's time to extrude the first piece.  It goes as a seperate solid from the boat hull.  I actually test made this part many times while drawing the former to make sure that I didn't have any extra non-construction lines in there messing up the section shape.  It's easier to catch it when you know what you just did to mess it up.