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 Sunday at 09:10 PM 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.