The Ship Model Forum

Finally, after thinking about and posting here two years ago, I want to begin building a 1/120 (88.7") BB61 as part of a model railroad module: (Wisconsin at ammo dock Port Earle) http://www.navsource.org/archives/01/016436.jpg

This will be my first ship model, scratch-built. I hope to get involvement here from interested modelers who can point the way for me and, while doing so, other newbies might profit, too. Wish I could be speedy like Song! But, my project will be slow to develop, at least at the beginning.

I have tabletop CNC mill and lathe and other tools that I wish to use extensively in this project. But, my first question is, how to proceed? Song built a drop dead gorgeous Iowa class model from wood. Do I want to use this material, too, or wood plastic work for be better, I wonder?

Do I want to draw a CAD hull form first, or just start with bulkhead cut outs over which a skin will be applied? Should I start with a keel is it that necessary? (I first thought I would go for a waterline model but now am leaning to full hull.)

Anyway, sure hope some of you will guide me along my path and pounce on me as necessary when I'm about to make a misstep.

Thanks!

Brian Chapman
Cedar Rapids, Iowa / USA

go with the keel & ribs as you will be doing a full hull.

You might want to consider changing your scale to a more common scale such as 1/125, 1/128, 1/100 or 1/96 as there will be fittings available.
I don't think anyone produces any fitting for modern USN ships in 1/120 scale.

https://www.shapeways.com/shops/model_monkey?li=pb

James

You could proceed in a couple of ways for the hull. You can make the frames and keel and "plank" the hull. Or you could make a "bread and butter" hull with layers stacked like the layers of a cake.

1. Planked hull. Since you have a CNC mill - and presumably a CAD program to drive it - you can draw frames in CAD and let the mill carve them from wood or plastic. The same goes for the sides of the superstructure. Of course the mill must have sufficient XY motion to cut the frames. I think at 1:120 the maximum beam width will be about 10.3 inches.

Many people use ordinary acrylic Plexiglass that is used for storm window glazing (typically 1/8" thick, or doubled up to get more rigid frames where necessary). It is easily glued together with acrylic solvent. Plexiglas is also good for the decks and superstructure.

Another option is to order 4'x8' sheets of polystyrene from a supplier like McMaster-Carr. This is MUCH cheaper than buying smaller pieces from hobby shops. You can mill frames and superstructure parts from these sheets. The styrene can also be used to cover the hull. It is easy to work with. Some time back a fellow posted on the Forum a build of a large scale destroyer escort made entirely of styrene. It was beautiful work. For finer detail parts the hobby styrene can be used (you can also order many of these pieces from McMaster or other on line suppliers).

Wood is another option, but I think it would be slower work than plastic, and require more work to get a good finish. But even if you make the model with plastic you might want to use wood for the wood decks.

Whatever the material the planking process for the complex curved surfaces at bow and stern will be a tedious process. Just assume that you will need to use auto body filler compound to smooth out uneven joints between planks.

2. Layered hull. If you opt for the layered hull you can cut short sections of the hull length to make up each layer. The CAD program and CNC mill would provide good accuracy for the section shapes. Just cut the pieces so the join between parts of one layer do not line up with adjacent layers in the layer stack. You can cut away the interior (leaving occasional cross frames for rigidity) to make a hollow lighter weight hull, with sides about 3/8" to 1/2" thick for good rigidity. Then sand the "jaggies" between layers to get a smooth hull surface. This would be a quick and easy way to get a good hull shape. It is an especially quick and easy way to make a waterline hull.

****

If you use CAD and the CNC mill to create parts of the hull (frames or layers) you should use the Table of Offsets instead of hull line drawings. The table is much more accurate than hull line drawings, and for a large scale model this is important.

The Tables of Offsets gives the numerical dimensions of the hull, perfect for CAD work. The Table gives points on the hull sides as XYZ values, where X is the length along the keel (or Base Line), Y is the width of the hull at Z elevations (you might want to make the Y value the elevation and the Z value the hull width).

The Table values are in the form F-I-E, where F = feet, I = inches, and E = eighths of an inch. So 10-7-3 is 10 feet, 7 and 3/8 inches, or 127.375 inches. Occasionally you will see a value like 5-9-7+. This is 5 feet, nine inches, and a bit more than 7/8 inch. I usually add 1/16 inch for each "+" so 7+ would be 15/16 inch.

The Table values can be used to generate the cross sections of the hull at each "Station" (X value) along the hull length for model frames. Or you can use the "Water Line Half Breadths" to generate the outlines of the hull at various elevations (waterlines). Think of the waterlines as if the hull was in a drydock and water was flooding in. Waterlines are where water meets the hull at different depths as the dry dock fills.

If you continue to post in this thread you can ask for advice about how to do things and get answers from others who have already been there, done that.

Phil

_________________
A collision at sea will ruin your entire day. Aristotle

I'm determined to do 1/120 scale since that's the railroad scale I'm working in. Kinda want to see how far I'm able to carry the scratchbuilding approach. Iowa (which I've been fascinated with for years and visited on three occasions) will be the centerpiece of the layout sections I wish to build.

I'm foolish to think about building a full hull. The scene I wish to model will have Iowa at pierside. I should model from the bottom of the boot upward.

I remain puzzled about the path to take building the hull:

1 - The Frame/Section approach with planks. (I know there's a difference between frames and sections but forget what at this moment.) As the stern and bow make their curves, will not the bulkhead edges need to be shaved to accommodate the skin? So that the bulkhead outer surface lays flat against the curving skin?

2 - Might be able to do a bread and butter layer hull by doing it upside-down. That way I could CNC cut the material to hull shape, which is broader at the main deck, narrower at the bottom fore and aft.

Cad drawing the hull:

1 - Table of Offsets - Searched online, perused the several ship plans (including TFD 1/96 1985), books and articles I have, nada. Do TOO exist out there somewhere?

2 - Table of Offsets would be ideal because then I could establish bulkhead shapes with precision and loft a shell over those points. Then proceed to draw bulkheads that perfectly mate with the shape of the hull.

Love the help I'm getting, thanks much!

-Brian

I loaded this graphic into a CAD program, sized it at 1:1 scale, and carefully traced the hull contours with spline lines (dark blue).

Please let me know what the vertical contour lines, numbered 1-20, indicate. A newbie question I know, but, then, I'm a newbie

The light blue horizontal line is where I'm thinking will be the hull bottom for this model.

Say, what do the letters 'KNU' indicate?

-Brian Chapman
Cedar Rapids, Iowa

Do you mean 11 to 20 on the left half of the diagram? They're for the aft half of the ship. The ones you've done in blue are only for the area between the bow and midships.

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De quoi s'agit-il?

The vertical numbered lines are "stations" spaced at intervals along the length of the hull. For US Navy ships there were typically 20 stations between "perpendiculars" along the hull length. The perpendiculars were the normal load waterline at the bow and stern - the length of the hull on the load waterline. Where the bow met the load waterline was called the "Fore Peak" (FP) and at the stern was the "After Peak" (AP). Station 0 (zero) was at the Fore Peak and station 20 was at the After Peak. Half stations were spaced between full numbered stations, typically forward of the Fore Peak and aft of the After Peak. Stations were just conceptual lines that were used to create the initial design. They were not actual parts of the hull construction. However, they are useful for modeling the hull.

The engineers drew up the initial hull line drawings using station lines and then used formulas or models to generate the mold loft numerical values for the actual frames. These are the numbers in the Table of Offsets. Frames were spaced at 4 foot intervals, with half frames below the normal load water line at 2 foot intervals. There were 216 frames between the FP and AP on the Iowa class ships.

I checked my blueprint drawing manual and found no mention of "KNU." A "knuckle" is a distinct sharp line or edge in hull plating. However, on your drawing there are no sharp transitions in the hull plating surface.

On the New Jersey drawings the 34' - 7 1/4" waterline is marked the "DWL" - Designed Water Line - where the ship would float without the normal load (fuel, ammunition, personnel, etc.). When loaded the ship would float a bit deeper. Your blue line is a bit too far down.

Phil

_________________
A collision at sea will ruin your entire day. Aristotle

Timmy C, yes, those numbers. I just haven't got to the aft half of the drawing yet.

Phil, stations, then (20 of them) are arbitrary and do not relate to frames or physical markers, they're for initial design reference only? So, iirc, the length of the ship between FP and AP (which I have marked on the side view of Iowa) is 860 feet. 20 stations divided into 860 feet is 43 feet between contours?

From this information, I can CAD plot the different horizontal WL levels of the hull's 20 stations by plotting where the WLs meet the hull, correct?

The Blue Line indicates the next WL below the top of the Boot, just wanted to make sure all the boot was included. Is this an adequate WL for the bottom of the hull on a WL model?

Thanks again. -Brian

I am working on an APA in 1:120 scale. Actually a rather easy scale to work in, digital caliper can be read directly in ones mind in feet and tenths of feet. My opinion (decidedly minority) is that scratch building should be just that with too much reliance on purchased parts.

It will be a large ship! Frames from plywood will be more rigid than plexiglass or whatnot, though I build a quite nice waterline Alaska in 1:192 from frames of styrene sheet covered with styrene sheet. Using thinner covering bow and stern made making the bow flares and so forth fairly easy.

Check out Hank Strub's build (completed) of the NJ when he served on her during Vietnam.

The stations were just for the initial design. They were not used for the actual construction, so if anything was placed at a station it was coincidence. Looking at the Booklet of General Plans for the USS Missouri BB63 (1950) the AP is at about frame 215. 215 x 4 = 860. 860/20 = 43 feet between stations.

The top of the boot topping is 37' 6" above the bottom of the keel. Lower limit of the boot topping is 26' 6" above the bottom of keel. So the boot topping was 11 feet high. Design Water Line (DWL) was at 34' - 7 1/4" above the Base Line, and the Base Line was 2" above the bottom of the keel. So the DWL was 34' - 9 1/4" above the bottom of the keel.

Most elevations (including water lines) are referenced to the Base Line, and not to the bottom of the keel.

You can use the station lines and water lines to plot the shape of the hull. But keep one thing in mind - the station lines show the INSIDE of the hull plating. This is called the "molded shape." So the actual width of the hull at the station lines would include the thickness of the hull plating. The plating was not the same thickness everywhere. To get the exact dimensions you will need the hull plating drawings. Generally, the plating is thickest midships, and thickness generally increases from the top of the hull toward the bottom - but there are exceptions. Also, station lines do not show any external armor belts, but the Iowas didn't have external belts..

At 1:120 scale the difference in thickness between 1 1/2 inch and 1/4 inch plating is about 0.010" or about the thickness of three sheets of notebook paper. So it isn't worth worrying about.

Phil

Note: Since you are building the model as a part of a model railroad layout, and it will always be indoors, you don't have to worry about thermal expansion.

But if you ever build a large scale model to be used out doors DO NOT mix wood and plastic! Wood has a very low coefficient of thermal expansion (doesn't expand much with heat) but plastics have huge coefficients! A three yard long piece of acrylic (Plexiglas) will expand about 1/4 inch in length when moved from indoor room temperature to outdoors in direct sunlight on a hot summer day. The forces produced by expansion are very large. If the plastic is fastened to a wooden frame something will have to give!

There are two posts (at least) on the Forum about 1:72 scale RC aircraft carriers where either the flight decks or sides buckled significantly when in direct sunlight.

_________________
A collision at sea will ruin your entire day. Aristotle

I've learned how to create the Iowa Class body shell using Fusion 360. I'm very pleased with the half-length hull I've created so far. The hull bottom curve about mid-way along the length looks squirrelly so might have to deal with that later. Although, I'm likely to do a waterline model.

I used stations 1/2 thru 11, this section measured 453 feet-plus. Spacing between sections is 43.2 feet.

Here are a few screen shots of the hull.

Brian Chapman / Cedar Rapids, Iowa

Looks to me as though the bottom curvature needs a consistent radius of curve all along the edge. I'll edit those to make them the same, which, I hope, will eliminate the bulge at the middle of bottom outside edge. And, then, maybe that will reduce the pinched area of the bow (terms, I'm still learning).

Brian C.

Looks a lot better than some of my attempts at Fusion. Looking forward to following further.

Matt

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In the yards right now:
1/350 USS Portland CA-33 1942
1/350 Trumpeter Texas with a twist

Hey, Matt,

Been waylaid several days now by something nasty from the planet Virus. Wanted to experiment more with the shell but haven't been up to it.

Where sides meet bottom, in the middle of the length, something doesn't look right, even though I precisely traced the station lines in CAD. Looks like the radii become larger, extending the radii up the side of the hull.

Not sure what to do about that.

Brian Chapman
Cedar Rapids, Iowa

Brian,

Looking at the hull sections in the USS New Jersey BB62 Booklet of General Plans it looks like the radius does get larger gradually forward of the vertical sides, and then the radius gets shorter again near the bow, so maybe your hull isn't wrong here. Most other battleships don't have the vertical sides, but American ships had to pass through the Panama Canal with locks only about 105 feet wide, so our battleships and carriers had the sharp radius at the bilges and vertical sides. But forward and aft of the widest beam the hull shapes were "normal" with varying radii at the bilges.

It does look a bit "pinched" aft of the bow, but the hull actually does this a bit because it is concave and wider at the upper flair and the bulbous bottom near the bow. It looks "pinched" to me because the transition from concave forward to convex aft seems to be too sudden. This could be due to a simple misplaced point on one of your station/frame curves. Been there, done that!

Just looking at the hull lines it would appear that the sharp transition is somewhere between Frame 13 (deep concave) and Frame 46 (wider radius and flat side).

However, this appearance may change as the hull is rotated and lighted at different angles. Your hull may be correct and just looks "pinched" at certain view and lighting angles.

One trick I have used to verify the curvature of a hull surface is to generate "contour" lines where horizontal planes intersect the hull at different elevations - the same as waterlines in hull line drawings. Any sharp kinks in a contour line indicate where a point in a frame/section line is out of place. This is especially useful when generating a hull surface from Table of Offsets numbers, because those hand drawn tables often contain slight errors. When the draftsman was copying lots of numbers from the engineer's notes there was potential for transcription errors!

Phil

_________________
A collision at sea will ruin your entire day. Aristotle

I feel as though I'm being rude, I've asked for help with my Iowa build and help has kindly been put forward. Yet, I'm missing from the board for days at a time. I'm still under attack from a viral URI and am without energy or clear thinking at the moment.

Thanks, fellas, for all the help. Phil, looking forward to digesting your latest message.

Brian Chapman
Cedar Rapids, Iowa

Matt, thanks for the encouragement!

In recent days I've been working on stations again in CAD, minutely correctly radii where the hull curvature meets the bottom of the hull. I'm going to start over in Fusion 360 and do the entire hull this time.

Phil, thank you for your insights. I'll have to learn a bit more about lighting in Fusion 360 and test more viewing angles. And, your waterline contour lines method to verify hull shape is very helpful.

I do not understand to what the half-siding lines, bow and aft, refer. Googled the term using ship design in the search term but returns were not enough for me to understand what they are.

–Brian Chapman
Cedar Rapids, Iowa

Speaking of the Panama Canal, one of my favorite photos: The 108-foot beam of Iowa edging through the 110-foot wide locks.

https://i.kinja-img.com/gawker-media/im ... h8rch4.jpg

Nice work, Brian, enjoying the discussion and your efforts!

If there are any Model Monkey products you would like made available in 1/120 scale to save you some time and effort, just let me know. Products in big scales can be done. For example, a client in Washington state is presently building a USS Iowa BB-61 model in 1/48 scale. Yes, really, 1/48 scale. The turrets, directors and some fittings for his ship are all Model Monkey designs.

Here are the 16"/50 barrels for his model:

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Have fun, Monkey around.

-Steve Larsen

Catalog of over 2000 products for scale modelers, most in 3D-printed gray resin - https://www.model-monkey.com/

On WWII era warships the very bottom of the hull often consisted of a flat keel plate (part of a large "I" beam) with additional plates welded to it on either side. These additional plates were called "half siding." Outboard of these were the "garboard strakes."

On flat bottomed ships the half siding was just half the width of the keel plate. On ships with upward slope of the plating outboard of the keel (dead rise) additional half siding plates were often welded to the bottom keel plate, at an angle equal to the angle of the dead rise.

Phil

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A collision at sea will ruin your entire day. Aristotle