⚓ Container Ship ⚓ ‿‿‿‿‿‿‿‿‿‿‿‿

My entry into the "Science: Make It Float challenge"

• The current featured photo is a float-test of a three-hull-section container ship with SIXTY rolls of pennies (8.311kg); 16 in the front section, 16 in the center section, 15 in the rear section, and 7 in the stern (for pitch balance), and 6 containers "on deck". Had to move to the tub; the ship won't fit into the cooler I was using anymore...
• In theory, this design can float an unlimited number of pennies, by simply adding more Container Hull sections, each of which can easily support the weight of 13-16 rolls of pennies.
• Videos
  • 60 rolls of pennies (8.311kg) floating in 3-hull container ship — final float test; That's all the penny rolls I have, and pretty much out of time. Lesson learned: lower the center of gravity.
    https://www.youtube.com/watch?v=ucUdUFSFkA0
  • Float test of 57 rolls of pennies (7.921kg)
    https://www.youtube.com/watch?v=lZGa6ZLCMuU
  • ✅ Successful float test of 47 rolls of pennies (6.531kg)
    https://www.youtube.com/watch?v=nlUAm5jXbFs
  • An early float test (one-hull-section ship) with 4 containers in the hold, each with a roll of pennies inside.
    https://www.youtube.com/watch?v=wgOmfVg2kX4
  • Adding 3rd Container Hull section / Assembly
    • Part1 — https://www.youtube.com/watch?v=iOW4JNv2nHk
    • Part2 — https://www.youtube.com/watch?v=9WbwUSZzHJY

See the Instructions for a narrative of the iterative discoveries, and design modifications that resulted.

See Updates below to see changes since first published.

This is definitely a "work in progress". Things may still change based on the ongoing printing, testing, and experimentation.

I normally don't publish my things until after I successfully print one myself and verify everything prints and works as designed. However, for this challenge, you get to "come along for the ride", and follow the progress, setbacks, redesigns, and hopefully, the ultimate success of this project. A chronicle of the process can be found in the Narrative section under the Instructions tab.

Concept

The first thing that came to mind when I read the challenge goal — to optimize the amount of weight your boat can support using coins in your local currency — was a container ship, having the containers hold rolls of pennies.

An object floats based on Archimedes' principle:

Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.                                              — Archimedes of Syracuse  

Therefore, in order for a ship to float, it must displace a volume of water that weighs more that the ship and its cargo.

So, the first thing I did was weigh a roll of pennies to determine the size that a container would need to be in order to displace a volume of water having the same weight.

The idea behind that, is that if each container itself is at least (neutrally) buoyant, then a ship's hull that would surround the containers should have enough buoyancy to float the hull and the containers in it.

That conclusion is based on the fact that the hull would displace the volume of all the containers in its hold, plus the additional volume of the space around the containers (weighing only as much as the air in it), and the thickness of the hull itself. Since the hull will be made of plastic, and not solid, the volume of water equal to the volume of just the hull itself should be enough to float the hull. i.e., If I filled the hull with water it shouldn't sink.

This would be difficult to calculate ahead of time (although, using the slicer's "filament required", and approximating the weight of that much plastic would probably be close enough. Note: I proved this to be the case experimentally once the hull was printed.

Penny rolls ranged from 127g to 133g. I looked up the weight of water — 1g/1000mm³ (it varies with temperature, and of course salt content in the ocean, neither of which should be factors for this model...). From that, I determined a "container" size -- having dimensions to surround a roll of pennies, and enough volume that the container itself should float with a roll of pennies inside. If each container is buoyant, then by definition, the ship itself should be buoyant if the containers all fit inside the hull, since the ship's total water displacement would be even greater. It should, in fact, be greater by enough to add a layer or two of containers on the deck, and still be buoyant. I didn't try to pre-compute that; I figure that will be done by simple experimentation once the ship is loaded and floating by adding containers to the deck. Of course the weight of the water displaced by the hull must be greater than the weight of the ship, and it's cargo — by enough to raise the deck of the ship high enough above the water's surface to avoid flooding the hull.

The design I came up with is modular so that

1. It will fit in the print volume
2. In theory, it is infinitely scalable by using one Bow, one Stern, and any number of Hulls/Decks (I'm hoping to print as many hulls as time permits to test that theory...).

The bow and stern make it actually look somewhat like a ship (vs. a square barge), and add some buoyancy since they are empty, which should allow for on-deck containers.

Another design goal is to only use printed parts (other than the penny rolls), without the need for gluing, and to have no parts that require support material (which, for instance, influenced the shape of the stern away from being relatively flat to be somewhat pointed (it prints on end).

• Note: In the end, the bow (second version) required support material; see Narration in the Instructions about that.

The hull part is sized to fit a dozen containers (4 wide × 3 high) based the dimensions described above.

I also incorporated a keel into the hull that can hold a roll of pennies to add weight at a the lowest point to aid in lowering the center of gravity, in an effort to increase lateral stability (to prevent the ship from rolling over).

In order for form a (reasonably) water-tight seal between the modules, there is a groove running the length of the joining edge of each piece. I employed a "gasket", printed with flexible filament, that is forced into the grooves, and the modules are then clipped together using 12 clips (ABS has enough "flex" to allow them to snap into place, while being rigid enough to hold tight).

• Note: The flexible filament turned out to be too rigid to form a decent seal like a rubber gasket would. I wound up using a different solution — see the Narration section in the Instructions.

Updates

• Jul 19
  • Added videos of 57- and 60-roll float tests of 3-hull-section ship.
• Jul 18
  • Added video of 47-roll float test of 3-hull-section container ship.
• Jul 17
  • Added 3rd Container Hull section
• Jul 15
  • Added 2nd Container Hull section
  • Floated TWENTY SIX rolls of pennies (new photos)
• Jul 14
  • Added a "12 Container Replacement" consisting of a "grid" (print 2), and a "bar" (print 4).
• Jul 13
  • Second float test (using plumber's putty between the hull seams) — success ✅ (new floating photo).
  • Deck Plate printed photos added.
  • New Bow printed, photos added.
• Jul 11
  • Uploaded new, shorter, Bow, Bow_108.stl — it fits within required build volume limits. I left the original, Bow_68.stl for reference, and an option if your vertical print volume is not limited to 150mm.
  • Uploaded new Bridge halves, that are not as tall (as printed)/wide (as assembled)
    • Needed to reduce the print height to fit into the MakerBot's printable area (150mm).
  • Uploaded new Hull Joint Clip
    • Stronger (provides more pressure)
    • Does not interfere with the containers (is not wider than the "seam ridge".)
  • Uploaded new Joint Clip
  • It floats! (see pictures)
    • Of course, it leaks too...
• Jul 9
  • Uploaded new (thinner gasket)
• Jul 8
  • Bridge pictures
• Jul 7
  • New (lighter) Container & Container Door)
  • new Penny Roll Holder (larger hole for roll, chamfered corners and slightly smaller outside dimension for easier fit into container)
  • new Container Door (looser fit, ridge on top for easier opening an look)
  • picture of completed container hull (one of hopefully 2 or more...)

Printing Progress:

• ☑ (1st revision) Bow
• ☑ New (2nd revision), shorter Bow
• ☑ 1st Hull
  • Containers (12) ☑ ☑ ☑ ☑ ☑ ☐ ☐ ☐ ☐ ☐ ☐ ☐
• ☑ Stern
• ☑ Gasket
• ☑ Hull Couplers (2)
• ☑ Hull Clips (12 per joint)
  • ☑ Bow/Hull (12)
  • ☑ Hull/Stern (12)
• ☑ Bridge
  • ☑ Port Bridge
  • ☑ Starboard Bridge
  • ☑ Bridge Couplers (2)
• ☑ Stern Deck
• ☑ Crossbars
  • Bow Crossbar ☑
  • Container Hull Crossbars ☑ ☑ ☑
• ☑ Deck plate
• ☑ Re-designed container
• ☑ 2nd Hull
  • Containers (12) ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐
• ☑ 3rd Hull
  • Containers (12) ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐
• ☑☑ ☑ 24-container replacement penny roll holders (3)

To-do

• ☑ Redesign Bridge
• ☑ Redesign Bow
• ☑ Redesign container (see narration)
• ☑ Design "Clip" used to fasten the hull modules together
• ☑ Print second (container) Hull
• ☑ Test flotation
  • ☑ New Container (success ✅)
  • ☑ (original) Container only, with pennies (fail ⛔)
  • ☑ Photos/video
  • ☑&☒ Is ship balanced?
    • The new bow is lighter, and displaces less water than the original.
      ☑ The ship floats level when empty.
      ☒ When loaded with 26 rolls of pennies, the bow sinks further than the stern, since the stern has more buoyant force being applied to it due to the greater displacement than the bow.
    • Shifting 4 rolls from the front container section into the stern leveled the ship.
  • ☑ Is it laterally stable, or susceptible to rolling? (I have a plan if it is unstable...)
  • ☑ Determine how many containers can be added on-deck, and keep the deck above the waterline.
• ☑ Print more Hull sections (time permitting)
  • ☑ 2nd Container Hull section
    • Containers ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐
  • ☑ 3rd Container Hull section
    • Containers ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐