The Ship Model Forum

Even if you used the Table of Offsets to set points in your CAD drawing you could expect a few bumps and strange curves.

An engineer did all of the calculations by slide rule and recorded the results by hand. Then a draftsman rewrote the engineers numbers on the blueprint. With thousands of numbers there were many opportunities for errors.

When I made my CAD model of the Cleveland class hull from the Table of Offsets, using Excel to create decimal inch equivalents of the foot-inch-eights numbers, I made a typos. I had about half a dozen "bumps" in the CAD lines. After correcting my mistakes I found four or five values in the Table of Offsets that were off by a foot, an inch or an eighth.

Then to get really smooth hull surface curves I had to do a bit of editing of the point positions on the section lines. It was a successive approximation process.

Phil

[quote="DavidP"]how did you go about getting the ship's frames from the drawing/plans to the cad screen?[/quote]

Placing the forward perpendicular (F.P.) on the origin, I offset planes along the X axis where to the aft of the ship. I created a canvas on the XZ plane that had the frames and generic shape. I also created a canvas on the YZ plane where I scaled (from conversations here, my scaling was off) the frames sketch and at each frame used that as my guide to trace. The sketches all matched the canvas, but when I went to loft between the frames there were a lot of issues with bumps and curves in incorrect places.

[quote="DavidP"]I would use the overall length of 673'5" divided by the scale to get 42.088" long overall. why are you using 1/144 scale & not the 1/192 scale as per your title?[/quote]

I will give that a try! And the 1/144 was a typo. I had been going back and forth between the two scales, but the 1/192 is what I am sticking to. Using that and doing measurements for where the waterline was on the previous rendering, at 20' I should see the waterline about 1.25" from the keel. It was 1.1". The length of the model i had was 40.1" so as you propose I think that might solve some of the issues I had with proportions.

I appreciate the challenge/suggestion!

[quote="DavidP"]sgrog04, how did you go about to get the frame measurements for your drawings?[/quote]

I think if I understand correct. I took the General Dimensions "Length Between Perpendiculars" which was 4'-0", then offset planes the length of the ship at 0.33" intervals (1:144 conversion), and then fit the the sketches in that X envelope. I also took the "Breadth Extreme" of 70' 9.875" scaled and did similar for the Y dimension. to get the Z dimension I knew the "Design Water Line" was 22', and scaled the Z direction for both plan sets.

[quote="DrPR"]The Booklet of General Plans is just an "executive summary" for people who can't tell the pointed end from then blunt end - for marketing purpopses.[/quote]

Best way I have heard it described by far. I'm more familiar with aviation blueprints as I've used them for WWII aircraft restoration, and professionally for work I use blueprints, but the naval prints are a little different then I am used to and appreciate the insight! Getting all reels will probably be the next step. The researcher I was working with mentioned there were over 30 boxes of items for the Saint Paul. I would have it all scanned, but the cost was a little prohibitive all at once. The more I dig into the ship the more questions arise.

Project is taking longer then anticipated, but the process has been fun!

The Booklet of General Plans is just an "executive summary" for people who can't tell the pointed end from then blunt end - for marketing purpopses. The drawings aren't very accurate.

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I don't recall much about the Baltimore Class blueprints. But the Cleveland Class blueprints were 19 reels of microfilm - mostly plumbing, wiring, furniture lists, key lists, nameplates over doors, and such.

If you are thinking of ordering blueprints from the National Archives try to get the index reel (usually reel 1). This lists all of the blueprints and you can find where the desired drawings are. Hull drawings are usually on the first reel, but things like propellers and turrets are on different reels. Unfortunately the Cleveland Class drawings didn't have a single index reel, but each individual reel had its own index. I had to buy all 19 in order to find all of the drawings I needed!

Note. The ships plans are in Record Group 19, and are listed on "reels." The Cleveland Class drawings are on reel 5537. However, this is a virtual reel, and the drawings are actually on 19 physical reels of microfilm. This can cause confusion! You can get the microfilm copied onto DVDs.

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Another source of plans is The Floating Drydock.

https://floatingdrydock.com/

Phil

[quote="DrPR"]sgrog04,

Did you use the Table of Offsets to create the stations in CAD, or are you working from the hull station lines drawing? Note that the Station 20/21 (midships) lines are not the same on the left and right sides of the drawings. There is a "step" or overhang on the right side but not on the left. Something strange there.

I found a similar peculiarity in the Cleveland class hull lines drawings. These hull lines drawings were mostly for show, and for the engineers to use for calculating the Table of Offsets. The actual hull construction used the Table of Offsets to loft the frames.

I did a CAD model of the Baltimore hull about 15 years ago. The knuckles are tricky. In my CAD program you have to mark points on the station lines where there are knuckles to cause the program to create the knuckle and not smooth it over.

It appears the knuckle is displaced high on part of the stern quarter.

Phil[/quote]


I do not have the Table of Offsets, only the hull station line drawings. I am thinking of putting in another request for data at the National Archives, and open to any drawing documents that may be useful. Right now I only have the Booklet of General Plans, and deck logs from 1966-1968.

It does look like it displaced high on the stern quarter. I think part of it is my frame spacing of 0.38" vs what should be 0.33" spacing. Minimal, but may account for the distortion partially. The other thing I am seeing is that my inboard profile goes from 2 to 164 for frames (with F.P. and A.P.), but the station line drawing goes from 1 to 39.5 -- Roughly the same number of stations, but the frame spacing looks off. Especially when doing a curvature analysis.

I think I will start from scratch again and try a new approach.
[attachment=0]Draft Analysis.jpg[/attachment]

sgrog04,

Did you use the Table of Offsets to create the stations in CAD, or are you working from the hull station lines drawing? Note that the Station 20/21 (midships) lines are not the same on the left and right sides of the drawings. There is a "step" or overhang on the right side but not on the left. Something strange there.

I found a similar peculiarity in the Cleveland class hull lines drawings. These hull lines drawings were mostly for show, and for the engineers to use for calculating the Table of Offsets. The actual hull construction used the Table of Offsets to loft the frames.

I did a CAD model of the Baltimore hull about 15 years ago. The knuckles are tricky. In my CAD program you have to mark points on the station lines where there are knuckles to cause the program to create the knuckle and not smooth it over.

It appears the knuckle is displaced high on part of the stern quarter.

Phil

[quote="DavidP"]these areas circled in red do not look right. does this look something like what you are using to get the shape of the frames?[/quote]

I definitely agree with that. And that does look pretty close to what I am using. The sketches match right, but when lofting that is where I run into troubles. The first 6 stations on the bow really need a lot of work.

Been away for a bit working on trying to get the hull form sorted out.

Turns out the bow is a quite complex! Main hull and stern turned out decent. Not 100% satisfied with the forecastle/bow, but it looks like it should work (nothing a little sanding cant fix). Open to thoughts, opinions, or feedback. To get this result, I used the hull lines, and placed at the correct frame, and manipulated the curves to get the right shape (more or less)...

[attachment=0]Hull V4 Bow.jpg[/attachment]

[attachment=1]Hull V4.jpg[/attachment]

Now with that done, working on the various components for the propulsion system, and for the superstructure I plan on making that as one detachable unit. Probably get the propulsion and internals done first so I can start printing and hopefully get testing done this winter season still!

We called the iron spheres used to compensate the compass the "Navigators balls". In aircraft a similar procedure is used to swing the compass, generally on a "compass rose". A compensation card is created giving the deviation between indicated and actual magnetic direction. Even the 747 had a small whisky compass (filled with alcohol). However the main magnetic sensing is done with a "flux gate" which senses the alignment of the earths magnetic field.

Have fun!

Actually the term is "swinging the ship" to align the compass. The vessel is turned through 360 degrees, stopping eight times so the ship's bow points to an object on shore of known position. After the ship's actual position is determined (compass readings, radar, GPS, etc.) the bearing to the distant object from a chart is compared to the compass reading. A deviation plot is created from these readings. The magnetic compass has several iron pieces that can be adjusted to compensate for tilt and magnetic anomalies caused by the ship's structure.

To turn the ship around a point engines on one side (port/starboard) are run forward and those on the opposite side are run in reverse. [b]The thrust from the ship's propellers (forward and aft) passes through the ship's center of gravity/mass.[/b] The trick to swinging the ship around a specific geographical position is to get the same magnitude force in the forward and aft vectors through the center of gravity. Since propellers typically are more efficient pushing forward than aft it is necessary to adjust the RPM of each engine to get the ship to spin around a single point. This is tricky and requires careful coordination with the engine room.

In reality water and air currents influence the ship's motion, as does the resistance to movement through the water of the forward and aft parts of the ship. The actual "point" about which the ship spins varies, but is fairly close to the center of gravity.

Phil

Having recently used a 3rd party to get a detailed print done in resin (Amateur Radio project), the cost would definitely be well justified for a larger project like this. It is definitely high on the list of things to investigate further while I draft everything in CAD.

The port/starboard separation makes sense. As I get the hull finalized, I will be looking at several drive systems. That is good advice to keep in mind!

For maneuvering it is best to have separate speed/direction controls for port and starboard engines. This is especially true for maneuvering to and away from piers and moorings. It is common to use a combination of forward/reverse engines and rudder to swing the stern of a ship away from the pier when getting underway.

With careful application of forward and aft engine controls it is possible to "twist ship" to cause the vessel to pivot 360 degrees around the center of gravity without moving forward or backward. This procedure was used to align the compass with known points on land around a harbor.

Phil

Just my opinion, but you might want to acquire a resin printer for detail items. The string printer probably better for hulls!

[quote="Fliger747"]There is some caution that going for too large a ship may result in a project that never gets finished.[/quote]

I fully agree with this!

Initially I was planning on a 1:192 scale as the Book of General Plans I have for the vessel would be a 1 to 1. Ultimately I wanted to maximize stability and scale size for being able to add things in the future (electronics to turrets, cameras, etc). To see if it fit in my constraints (wall mount, and in the back of my car) I made cardboard cut outs at the different sizes and the 1:192 and 1:144 both fit, the 1:96 scale was to large for my constraints. I also test printed parts at the three scales on my 3D printer, and the resolution was okay, some of the detail issues could be solved by using a .2mm nozzle and having finer resolution (small widgets like hose reels, 3"50 turrets and radars/electronics).

I have a workbook I created to compare the sizes, and take around 30 known measurements and come up with scale equivalents.

In terms of current steps, I am jointly working on Rev 4 of the hull, and working to determine what level of detail I want as it will be "mounted" for display in my house and will be a lake worthy model (along with future projects of USS Nashville CL-43 and USS Minneapolis CA-36). Ill probably try to incorporate things like ladders, antennas, search lights, but not sure how much detail I will include.

Not rushing the design process as I want to sort through as much ahead of time before building to try and save some headaches long term.

There is some caution that going for too large a ship may result in a project that never gets finished. As you have Fusion 360 and I presume a printer, you will find that you will probably desire to make all the other components yourself. The scale will become irrelevant. A 144 ship will be about 2.4 times the volume of the 192 version.

Good luck!

That would probably make for a simpler drive train, and be better for steering I would imagine too. All good feedback!

It has been a minute, and several dozen hours drafting away in Fusion 360. Currently I am on version 3 of the hull (I am good with nice simple geometries like bikes, or RV trailers), the complex geometry, especially of the bow and stern are proving to be quite a challenge (I will get there eventually)! Mechanically and widget wise, things are coming along decent!

Due to part availability, and ease of fitting into my work space, I found that 1:144 scale will work better then the 1:192 scale initially planned. Plus it will be a little more stable on the lakes near me (Reality, anything more then a light breeze will be like being in a sea state of 10 or higher, so Ill have to find calmer bodies of water - Some get up to 6 foot waves, probably a good day to leave the model in the shop).

In version 2 of the hull I started working on the superstructure, but want to hold off until I can get the hull ironed out. I found a great hull tutorial/guide here: [url]https://modelshipworld.com/topic/28912-how-to-design-ships-in-fusion-360-and-3d-print-them/#comment-825624[/url]

Propulsion wise, I am looking at using two brushless motors powering a gearbox with one motor going to the two outboards, and one combo going to the two inboard propellers.

Image should post with this here, not my best work, but it is a work in progress, learning a lot along the way, and finding out about all sorts of history, and going down the rabbit hole (Plan to build the USS Nashville CL43, USS Minneapolis CA36, and maybe the USS Duluth CL87 - notice a slight trend towards cruisers?).

[quote="DavidP"]digital version of the Booklet of General Plans or paper?[/quote]

Digitized version of the Booklet of General Plans. I worked with a Research Consultant.