Keel ballast

[Antonello]

Hi all.
My name is Antonello and i’m writing from Sardinia Is., Italy.
I’m interested in model boats and I have recently dowloaded D.S. wich is a powerful tool to design them.
I think the program is quite straightforward, almost in its basics, but I had some trouble trying to design the “torpedo” keel ballast.
Some suggestions?
Many thanks in advance
Antonello

[Martin]

Can you send a picture of “torpedo” keel? I don’t know what you think. 😉

[Antonello]

Thanks for the reply.
Hope it helps…

Ballast is missing and must be added:

[Terrance Egolf]

Hi Antonello.

If I were given this problem, I’d probably use the “brute force” method, since I’m a fairly new user myself. Others here might be able to propose something more elegant.

First thing I would do is create a scale schematic of the ballast. This can be done on paper or a CAD program. Add sufficient stations along its centerline to define its shape. More stations will be needed where the curvature is high. Measure the position of each station from some longitudinal reference point and note these on the drawing. Also find the scale radii of the ballast at each station. I would also find the ratio of all station radii smaller than the max radius to the max radius (R_station/R_max). Write these ratios prominently next to each station on your diagram.The reason for this will become apparent soon.

DELFTShip has an Add Cylinder tool in the 3D Primitives menu. Make the radius of the cylinder the same as the max radius of the ballast. I’d specify enough points to make a smooth cylinder (e.g., 12). The cylinder length doesn’t matter because you are going to delete everything but one circular end surface after it’s created anyway. Set the start and ending coordinate along the DS x-axis and place it at the z-location corresponding to the axis of the ballast in the DS model. The cylinder’s y-location should be 0.00.

After deleting all points and lines except for one circle, move the circle (a disk, actually) to the position of the max radius station of the ballast in your model along the x-axis.

Next, select all the edge segments of your circle (and nothing else!) and use the Extrude edge tool to extrude the circle to the first station x-position.

Then select all the edges and control points of the extruded circle (and nothing else!–I am always forgetting to deselect a random line segment or control point when moving, splitting, or deleting …), then scale them to the scaled radius of that station using the Scale tool in the Transform menu.

Repeat as many times as necessary for each station in both directions from the max radius station. The ends of the shape can be modeled as very small circles rather than trying to model hemispheres or whatever (this is why more stations are required closer together where the curvatures are highest.)

You should end up with a fairly accurate representation of a torpedo-shaped keel ballast. If you created this ballast in its own layer. You can turn off the rest of the model while creating it, which will make things easier to see.

Hope this helps. As I said, this is a pretty crude way of dealing with this problem.

Terry Egolf
Greenville, South Carolina, USA

[Martin]

There is nothing I can add. Maybe I have one tip for you only. I prepare a bulb in software BulbCalc: (http://www.onemetre.net/Design/Bulbcalc/Bulbcalc.htm)
This software help you to do a blueprint of bulb what you create by primitives as tegolf wrote.

[Antonello]

Many thanks for your most kind replies, this metod seems quite straightforward. Good manners are always paying but sometimes a litlle bit of a crude force can be extremely useful. 😉
I will let you know about the results
Cheers for now
Antonello

[Antonello]

Thanks to your help the problem of the design of the ballast has been solved. The solution, as said, could not be very elegant but it is valid to all practical purposes……..
Well, now I can start building the hull.

[Antonello]

Thanks to your help the problem of the design of the ballast has been solved. The solution, as said, could not be very elegant but is valid to all practical purposes……..
Well, now I can start building the hull.

[giorgio zuppin]

Hello there.
A nice way to use NACA sections as in BulbCalc, AND remaining in DS:
Use keel and rudder wizard in Tools, then with a bit of tweaking ( or black magic as you like ) it is possible to model a nice bulb, even one with a castor tail shape,
Here it is:
torpedoballast.pdf
I omitted some steps of course, if you need help, just ask.
Bye, Jurgen.

[Antonello]

Thanks Jurgen,for you patience in doing this extremely nice tutorial, in the next future I will put the patience of the members of this forum to stress when I will ask for some explanations how to model a ship from exixting drawings…

I will try also to model the ballast this way.

Cheers for now.
Ciao
Antonello

[Antonello]

Hi all
with the previous version of Delftship I was able to design the keel ballast, as shown in the #4318 post, in a very straightforward way, simply creating a cilinder, extruding one face, ten scaling it to have a cone and so on. Everything went very well.

After a couple of months I have to design a different keel ballast for my new RC sailing model but this time I did not sort it out in any way.

I’m myself that doesn’t remember the correct procedure I used then (getting older…) or, in this new version, the procedure, in particular for the “Scale” command, has somewhat changed?

With thanks
Antonello

[giorgio zuppin]

Antò, fa caldo… – sorry, I promise, no more Italian –
I’ve made a quick check: no changes is SCALE et al.

Try again and let me know.
Bye, Jurgen.

[Antonello]

Ciao Jurgen!

fa caldo…. e andiamo in spiaggia a mettere le barche in mare!

Thank you for your kindness: I will check again (I’m trying to do a detailed step by step report of the method I’m trying to use) and will let you know ASAP.

Thanks a lot

Cheers for now

Antonello

[Antonello]

(Wrong) Procedure to design a bulb

Step 1
First of all I draw the ballast, using Bulb calculator and drawing a schematic on Autocad.
Pic. 1

Step 2 –
Project opened in Delftship.
Pic. 2

Step 3
Draw the bulb. Starting from n° 3 part and placing it in a convenient place so that the bulb is in line with the bottom of the keel: z= -60, lenght is 3,77 so I place start point 50,00, end point 53,77, max diam. 2,56, min. diam. 2,27, y = 0
Pic. 3

Step 4 – First cilinder, or better, cone, is created.
Pic 4

Step 5 – Left points selected as I will try now to extrude part n°2. Longitudinal direction 1,84, transverse direction 0,00, vertical direction 0,00 and OK.
Pic 5

Step 6
Second cilinder extruded. First perplexity: why the extruded ciliber is green color? Shouldn’t it be grey?
Pic. 6

Step 7
Trying to scale the left side of the extruded cilinder.
Left points selected
Pic. 7

Step 8
Values to scale added: left side of the cone should be of 1,80 in radius while the right side is 2,27: so 1,80/2,27 = 0,793. Longitudinal = 1.
Pic 8

Step 9 – OK, and this is the result:
Pic 9

I tried several times, but with no results, and I can’t find where my error is….

[Icare]

Hi Antonello!

STEP 6: Why is the extruded cylinder’s color green instead of grey?
I assume you created a new layer for the bulb, but when you extrudied it the HULL layer was still selected, so the new surface was drawn on the HULL layer. Toggle the HULL layer invisible/visible, I guess the bulb will disappear/appear, too. :whistle:

STEP 9: Why does the SCALE operation moves the selected items?
The SCALE operation uses the coordinates’ origin point ( 0,0,0) as reference point, NOT the center of your selection. If you want to avoid this translation you must move the selected circle to the (0,0,0) coordinates, scale it, then move it back to its final location…
But the best way would be to design the whole bulb around the (0,0,0,) coordinates (either in your final drawing, either in a specific file you’ll export/import as a ship’s part) then to move it to its location.

I hope it’s clear enough… 😉

[Antonello]

Thank you Icare for the kind reply.

Step 6 – No, the bulb is on a separate layer and, being the extruded cilinder below WL it should be grey, exactly as the cone, AFAIK.

Step 9 – I will try the metod you suggested.

[Antonello]

Sorted out, thanks to all who willingly and patiently answered my question.
As Icare suggested, it is of the utmost importance to build all around the 0,00 line, a thing that probably in a previous design I did absolutely by chance.
During the construction the colors seem to appear at random and shape is very rough as more sections will be neeeded

but once collocated the ballast in the actual location the colors went OK

and all the hydrostatic calculations are fair.
Now I will do a detailed tutorial to bear it in mind.
Thanks again.

[Antonello]

Tutorialfinale.pdf

I did this small reminder to bear the method in mind in the future ( at 64 memory is running out…) and thanks to Taby, Tegolf, Jurgen 54 and Icare that replied my posts and gave me their help. Of course I will be grateful to all those who will signal errors or more elegant ways to solve the problem.
Cheers for now
Antonello

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