Amanda F Lewis 1884 by SardonicMeow - Scale 1:48 - Chesapeake Bay pungy

[SardonicMeow]

Welcome to my build log for the Amanda F. Lewis, built in 1884.  She was a pungy, a type of schooner unique to the Chesapeake Bay.  This will be a plank-on-bulkhead build at 1:48 scale.  There will be lots of 3D design, there will be pirates, maybe a road trip or two, no doubt plenty of successes and mistakes.  I hope you will follow along.

 

Below: 1933 painting of the Amanda F. Lewis by Louis Feuchter, painting photographed by me at the Chesapeake Bay Maritime Museum.  It shows the vessel during her later years.

[Jim Lad]

A nice looking vessel, peter.

 

John

[Paul Le Wol]

Peter, I am looking forward to seeing you create this beautiful schooner. Good luck with her!

[ccoyle]

I once had a student named Amanda Lewis. She was born considerably later than 1884, obviously. 🙃

[JacquesCousteau]

I'm looking forward to following along on this build!

[SardonicMeow]

I order the Amanda F. Lewis plans from the Smithsonian.  The ship was surveyed as part of the Historic American Merchant Marine Survey in 1936 or 1937.  H. I. Chapelle drew the plans in 1956 based on that survey.

And, wow, they're big.  The scale of the plans is 1:32.  Hmm, if I made the model in that scale, it would be just about 1 meter from tip of bowsprit to tip of boom...  Tempting, but I think a model that large would trigger a spousal veto, so that's a no-go.  1:48 is what it'll be.

I put the plans on one wall and photographed them from across the room.  The various views were put into separate image files and brought into the Autodesk Fusion environment.

Offset planes were created for each station position.

As well as for each waterline.

And for the buttock lines and diagonals too, though they might not be used.

And with that, the 3D environment is ready for design work.

 

[MAGIC's Craig]

A very sweet-lined hull. I look forward to following along with your build.

 

Craig

[SardonicMeow]

Let's use the imported plans to create the shape of the hull.

 

I start by going into Fusion's Form environment, which allows the creation of smooth objects out of t-splines.  It begins with a single face, strategically placed between stations 7 and 9.

The face is tilted outward at an angle consistent with the deadrise at that point on the hull.

And then the face is extruded until there are five faces total.  I found through previous experimentation that five was a good number.  Fewer faces and I didn't have enough control points to create a matching curve for each station.  More faces and the curves started to get wobbly.

 

This picture shows how the grid of control points and lines (black lines) define the shape in gray.  In most of the later images, I have hidden the control grid so that only the hull surface is displayed.

Each edge was adjusted to conform to the hull curvature at the stations (7 and 9 in this case).

Here is the same viewed from a different angle.

Then the forward edges are extruded toward the bow to create the next section.

And the new edge is matched to the curvature.

 

And the same procedure was repeated for each station going forward.  Note that I subdivided the grid between stations 7 and 9, and between 5 and 7, so that the spacing between grid pieces would remain consistent.  Failure to do this caused the grid to abnormally stretch in a disproportional manner as new stations were added.

It's starting to get  a nice shape.

Trying to get the shape right at the bow was trouble.  There is probably a clean way to end the form in a shape that matches the curve of the stem, but I don't know enough about the Form modeling environment yet to do it.  Instead, I just continued to extrude the form out and tried to match the correct form at the bow.  There is some pinching and distortion of the form here, but that portion of the form is beyond the boundaries of the actual hull, and none of the shape at that point will be used.  So it doesn't really matter.

With the forward portion of the hull complete, I started the same process working aft.

Here it is after a few sections are completed.

And compete all the way to the final recorded station. I'll have to wing it later to capture the shape of the stern.

Now I have two halves.  It was necessary to work in two pieces separately, because if I tried to create it all at once, the forward pieces would, in a head-on view, obscure the aft pieces, making it impossible to view them as I worked on them.

There is a feature to merge edges, which I used to unify the two pieces.

After exiting the Form environment, it looks like this.

How accurately does the shape conform to the lines of the hull?  Well, we can validate it by generating new lines and comparing them to the plans.  Fusion has a great feature that lets you plot the intersection of a form and a plane.  Let's do that, first with the section lines.  In the image below, I have already plotted stations 1 and 2 (purple lines) and I'm currently plotting the intersection of station 3 (red line).

After plotting all the forward sections (purple lines) they can be compared to the plans.

And the same for the aft stations.

It looks good.  Let's check the waterlines too.  Below, I waterlines 1 and 2 (purple lines) have already been plotted, and I am plotting waterline 3 (red line).

Now all the waterlines are compared to the plan.  It's not 100% perfect, but at this scale, the deviation is no more than a millimeter.  I'm satisfied.

So, what's the point?

 

First, let's mirror the hull shape.

Let's consider how this can be used to create a plank-on-bulkhead model.  I can choose any point along the length of the hull for a bulkhead.  At the point where I want a bulkhead, I can plot the intersection of the hull form and the bulkhead plane.

Add the deck camber and a notch, and I have a pattern for cutting out.

So I'll need to decide how many bulkheads I want and where they will be.  I also need to sort out the exact camber of the deck.

 

But there is one big problem with my hull form that means I can't use it until it's addressed.  If you've been reading all the notes on the plans, maybe you've noticed what I need to take into account.  This has been a big update, so that issue will be saved for next time.  Thanks for reading this far.

 

Edited May 18 by SardonicMeow

[SardonicMeow]

Last time I created a hull form in Autodesk Fusion.

At the end of that log, I alluded to an issue with the work I had done so far.  The problem that I have, is here on the plans.  The lines are to the outside of the hull.  That means that if I use the hull form as it is, create bulkheads with it, and then plank the model, it will be wider than it should be.  Instead, I need to create bulkheads that represent the hull form at the inside of the hull planking.

Fortunately, Fusion has a powerful feature called offset that handles this.  It can create a surface offset by a given value that is normal to that surface.

So I select my surface and create a new surface offset by the plank thickness.

Here are the old and new surfaces.

I generated station lines for the old a new surfaces at three points on the hull to show how the thickness is maintained.

This diagram from the plans shows a cross section of the hull.  You can see how the hull and deck planks lay.  Note also the wale or "bends", above which the planking is thicker.  The underside of the deck meets the hull planking at the gunwale line.  I want to create bulkheads that match the inner side of the hull planking and the underside of the deck planks.  I have shaded in green the portion of the target bulkhead shape.  The next task will be to define the underside of the deck.

Here is a view on the plans from the side.  The gunwale is clearly marked.  The deck at the center line is indicated with a dashed line.  Is that the top of the deck or the underside of the deck planks?  I can see that the mast coats are above the dashed line, so it must be the top surface of the deck.

Because I need the underside of the deck, I just traced the line of the deck surface at the centerline and then created a new line offset down the thickness of the deck planking.

Then I found the intersection of the edge of the underside of the deck at the waterway by intersecting the gunwale curve with the hull form.  (I mirrored the hull form before doing this, so I could get the curves on both sides.

Then I found the points where the odd numbered stations intersect with the gunwale and centerline at the underside of the deck.  I joined these points with a curve.  Here it is at station 1.  There is almost no deck camber here at the bow.

And these are the camber curves (black lines) for all the odd numbered stations.

Using those curves, I created a surface which represents the underside of the deck.

The surfaces are displayed here.

And here is an example bulkhead (light purple lines) created by finding the curves at the intersection of the hull and deck surfaces.  (As you can see, I also added some dowels for the masts.)

This is good progress.  I'm just about ready to create bulkheads.  I still need to work out the form of the stern, which I dread, so I'll be putting that off.

 

 

[SardonicMeow]

I created cylinders of diameter equal to the dowels I will use for the masts.  They were placed at the correct rake and ended where the dowels will end in the hull.

I was not satisfied with the hull from before, so I gave it another go.  The bow is cleaner and I also extended the shape aft beyond the last station on the plans.  This will allow me to identify the shape for a bulkhead as far aft as I'd like.

I also extended the deck surface fore and aft so that it would be available for finding the top surface of bulkheads wherever I choose to place them.

Now it's time to create the bulkhead shapes.  First, I need to choose where the bulkheads will be.  There are few restrictions.  I started by placing the bulkhead locations on either side of the masts to be sure that there would be space for the bottom ends of the masts.  After that, it was generally even spacing, with bulkheads closer together at the bow and stern.  This is a lot of bulkheads, but I hope it will make it easier to plank the hull.

The process of creating the bulkhead shape is straightforward:  Start a new sketch on the plane of the bulkhead.  Use the Project/Include -> Intersect tool to acquire the lines of intersection with the hull and deck shapes.  (The red line in the image below shows the plane of the bulkhead intersecting the hull.)

The result looks like this.

I add the notch at the bottom.  It is sized to match the thickness of wood sheet.

The superfluous overlapping lines are removed.

Repeat the process until all the bulkhead shapes are formed.

I can thicken these to get an idea of how it'll look.

And I quickly sketched out the keel to get a better idea of the final form.  This was just a quick shape to visualize how things will look.  The final stern post / keel / stem will be a little different.

To do next:

Add some shapes at the bow to help define its shape.

Add pieces to form the transom and stern.

Inscribe fairing lines on each bulkhead piece.

Inscribe lines on the bulkheads to indicate the line of the wale.

Add pieces to hold the masts in place.

Finalize the shape of the false keel, add the rabbet, etc.

 

Edited May 26 by SardonicMeow

[SardonicMeow]

I'm working on refining the 3D design.  I now have what lots of kits call a "false keel" - the internal piece that the bulkheads are glued to.  And I traced out mock-ups of the stem, keel, sternpost, and rudder, though those aren't in their final form.  Note the thin gap between keel and body.  When I build this, I will place a thin 1/16" x 1/16" strip in that gap to act as the rabbet.

I'd like some extra surface at the bow on which to start the planking.  Using the design at this point, I could place two pieces at the bow as shown.

I'd like to see how that will work once the bulkheads are faired.  I can visualize that by first finding the intersection of the bulkheads with the hull inner surface.

And using those intersection lines, I can trim the bulkhead pieces so they appear as they will be once faired.  Here, the first bulkhead and the two new pieces are faired.  First, it seems like there isn't much point in having the first bulkhead so far forward.  Also, the new pieces are so small that they only help for the uppermost hull planks.

Instead, I thought to add much larger pieces at the bow, as shown below.

This shows the design with the new pieces as well as the first two bulkheads faired.  The forward-most bulkhead has been moved aft slightly.  I think the surfaces now will make things easy to handle all the hull planks at the bow.  I still need to cut out new notches in the pieces to accommodate the new form.

[SardonicMeow]

Let's look at the stern.  The aft-most bulkhead has a problem.  The notch I originally planned isn't correctly sized, and any notch I do make will leave little to no room for the pieces to join.

However, I wanted to add some pieces anyway that would define the end of the transom and provide a surface for the stern piece to attach.  They can also strengthen the whole aft structure.  And they provide a solution to the issue above, because the final bulkhead can be attached to them.

The aft-most bulkhead still needs a notch so that there is room for the stern post to rise behind it.  (The stern post appears in the picture above, but not the one below.)

Next I worked on determining the fairing guidelines of each bulkhead.  This was done by finding the intersection of the hull surface with the forward or aft edge of the bulkhead.  An example of the final design of a bulkhead piece is below.  Note the short horizontal lines on each side.  Those were added to mark the lie of the wale on each piece.

Using the fairing lines, I created faired versions of each bulkhead piece within Fusion.  The animation below shows the difference between the pieces before and after fairing.

Let's check by todo list.  Some items are complete, and some have been added.

 

Add some shapes at the bow to help define its shape.

Add pieces to form the transom and stern.

Inscribe fairing lines on each bulkhead piece.

Inscribe lines on the bulkheads to indicate the line of the wale.

Add pieces to hold the masts in place.

Finalize the shape of the false keel, add the rabbet, etc.

Add the remaining notches so that the whole thing fits together like a puzzle.

Save designs and create laser cutting layout.

Take it to be laser cut.