Figure out the Figures

Discussion in 'Boat Design' started by RumnCoke, Sep 4, 2013.

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RumnCokeJunior Member

Gentlemen,
The figures represented in the attachment are the actual math values in percents, inches, and decimals. This paper represents an actual model hull design. I know it is not the common way things were done back in the day when boats were designed without computers and 3d boating software, but it was a kind of short-hand representation. The guy did all the algebraic calculations the old fashioned way, with his brain. The man was an airfoil designer for Curtis Wright back in the day and then contracted by the Navy to do planing hull ship design. He designed many private craft boats in his day as well as cars and airplanes. This particular racing design has already been an established winner.
There has to be some of you out there who can still make sense of it. After staring at this for quite some time now can almost make complete sense, but it would be failure for me to try and tell someone else what it all means from an actual drawing perspective. This is what I need, a drawing perspective.
Let me start by saying that the first vertical column "Unit %", 0 down to 100 each represents a sectional station. 0 is the Bow and 100 the stern represented in incremental percents as it states at the top of the column.
The second vertical column header defies my interpretation, but I read each descending value as the actual distance "inch.decimal" from the bow. So the percent figure in the first column, is now turned into an actual value.
The third vertical column "Plan" I believe is the distance from centerline on the boat to sheerline.
Fourth column is pretty self-explanatory. "Sheerline" vertical profile values at each sectional station.
Fifth column "Profile". I believe is Keel line values from centerline.
All that remains are the actual radius values at each station. This is where is gets a little fuzzy for me. The percent header values either work down from the center line or up from the keel line or at some distance in between. I am not sure where the line actually starts. Where it ends, of course, defines the sectional hull curvature between sheer line and keel line .
There are two sections of figures remaining on the paper. The middle section is describing radius, but I am not sure if it is a horizontal radius line running from bow to stearn or whether its just actually a Cross-sectional value describing radius at that point. The third section of headers has a big C.S. at the top which leads me to believe that these sets of values are the cross sectional values. So one section reads from a profile point of view and the other a cross-section point of view?
So is it one boat or two with just different radius values?
I know some of you "Heads" have got to catch on lol. Please it means a lot to me.
I will try in my layman terms to answer any questions.

Best,
RumnCoke

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2. Joined: Aug 2007
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rwatsonSenior Member

You probably don't want to hear it, but the quickest way to decipher the solution is to put it up in 3d boating software. That way, you can see the result of the numbers instantly, and adjust the interpretation until it works.

I can read the figures, it is not too dissimilar to many manual lofting instructions.

I would love to take it on as a project, but I cant drum up the enthusiasm. You may have to 'inspire' someone with money to get it done.

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Mr EfficiencySenior Member

Talk about having a "head for figures" ! I would find it very hard to believe that all those numbers were arrived at without reference to a drawing of some kind.

4. Black The MacPrevious Member

Mr. E,

I couldn't agree more.

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TANSLSenior Member

table of offsets

Obviously that's what you need to do, in 3D with a computer, or 2D drawing it on paper. To do that the first thing to know is what each row and each column mean as well as benchmarks for each measure, which is PRECISELY what RumnCoke is wondering.

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rwatsonSenior Member

Yes, he is asking for interpretation of some items, but doing it on paper and/or 2d would be oh so tedious.

With 3d, you can see it in real life as the figures get interpreted.

Many of those figures are very straight forward, and will serve as a baseline.

The ambiguous sections can be entered, and if they don't conform to the understood figures, you can experiment with the numbers until they make sense.

"All that remains are the actual radius values at each station"

How tedious it would be to see if an 'arc' fits, and where it starts, and if it creates a fair hull if you were doing it in 2d ? Its all about the amount of work you want to do.

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nzboySenior Member

Its just a normal table of offsets. Im a bit busy with work now But maybe its about 90 minutes of work to plug the numbers into freeship for example. Im sure some one else can do that before I can get around to it . 1988 wasn't that long ago .You know we actually had calculators so did not need to use our brains While hull programs are great to get a 3d of the hull I find it easier to draw cabins in 3d on a drawing board than computer

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TANSLSenior Member

rwatson, I see that you have very clear ideas which, unfortunately, is not my case. I've only got what appears in the figure below. And for that, I had to work the 2D frames because the frames are flat elements. Then place them in their true position in space is a cinch. Could you, please, tell us what you get with your procedure and explain it a little further?. Thank you

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9. dskiraPrevious Member

Is the "guy" was Rabl by any chance? He used this technique to design ship, but always starting with the coordinates from an other ship. It speeded up the process and made it more accurate.
Rabl used to work at the design and lofting for airplane as well.
Several shipyard used their own mathematical formula to fairing the hull, speeding up the lofting process on the floor.
When a ship was designed, due to the scale, the most important process was to fair the line, since it was the most time consuming work on the floor. Every bit of help by mathematic during the design stage was welcome by the loftman.
But I can mistake and misunderstand what you are asking.

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TANSLSenior Member

The problem, in my opinion, is to know what represents each row or each column and from which point are measured coordinates each cell of the table represents.
Lets assume, for example, columns 7 and 11 in row 5 are half breadths of the frame which is 0.492" from the aft end. According that its lowest point is 0.16" from an origin, which is unknown.
If we go to column 5, which seems to be the coordinates of the longitudinal profile, at the distance of 0.492" from aft end, the profile height is 3.761". That point should coincide with that of the previous frame. But not so.
How to interpret this?
A very interesting problema than, perhaps, technicians before the time of personal computer can solve more easily. Let me add the following comment, that no one has asked me for : it is always necessary to know how things are done manually in order to make them correctly with your computer.
Cheers

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RumnCokeJunior Member

Yes, Ted had some "Power Curves" he used to design the hull. These curves are what he derived from Flow in model testing.

@Nzboy-- Yes it is just a normal table of offsets. I have a paper that describes the values of the offsets he was using. I can post them in a moment if that will help.
These should only be used as samples of his method.
My goal is to put these figures to Boat Design Software but until I understand as Tansl is wanting to understand it will not be possible. The ultimate goal here is to put this design into Software then into CNC format for a plug.

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SamSamSenior Member

Here's my contribution. In the last column, the second row up from the bottom, I think the number should be 2.034.

Yes, post the offset values please.

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RumnCokeJunior Member

@Dskira-- Well at least you see it for what it is. His name was Ted Thorsen. Yes, he did much the same work for both Airfoils and Planing Hulls for the Navy.

This is the hull that is under discussion. It is about 90 percent true to the Figures on the paper. It had been modified a little so its not 100% true.
You can see the shapes for reference though.

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14. Joined: Sep 2011
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TANSLSenior Member

Yes SamSam, you are right, the last column and the 5th one should be equal.

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rwatsonSenior Member

I am not sure what you are meaning here.

The picture you posted is 3d cad - I can see the Z co-ordinate in one window, so I am confused about your reference to 2d.

Your representation of the hull form based on flat frames is exactly what I was talking about.

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