Question on hull scaling?

[bigdave]

OK all you members out there in the know.
I have a question.
Let’s say I have a hull and it is small in size and I would like to make rib patterns that I can scale up.
Are you with me so far??
Let’s say I do not want to cut sections out of my expensive smaller model and scan them.
What would be the best way to make the rib patterns without destroying the model??
I mean I could probably figure out a way to do it but I find it is best to ask the question first to see if someone that has done this is out there.
Also asking the question is a good way for people who may want to do this someday to find out as well.
All answers will be greatly accepted. Thanks, BD.
BTW- It is not a round type sub hull. It is a boat hull.
Yes I said boat!

[raalst]

I'm not sure what you

I'm not sure what you mean by rib patterns. do you want the hull look battered with the ribs showing thru ?

[Guest]

I posted this over at

I posted this over at Sub Pirates sometime ago.it was aimed more at those wishing to make a sci-fi type boat, which are often difficult to nigh on impossible to find drawings for.

If you fancy modelling a particular subject, but drawings are either impossible to obtain or non-existent, i.e. many science-fiction boats, what can you do?

Well you have a couple of alternatives.

1. Gain as much photographic evidence as possible either from film frame grabs, stills etc, and extrapolate data from that using paper and pencil to produce some working drawings.

2. Look to see if there are any commercial models available, in a smaller scale perhaps. Plastic kits, diecast toys etc. all fit into this catagory. These can often be inaccurate, after all the modelmaker making these often has to use quite crude methods to obtain any reference material, so it’s often wise to compare any model with reference material gleaned using method 1.
From these models, measurements and profiles can be taken that enable us to produce a working set of drawings that will allow us to scale up or down and produce a model suitable for our needs.

3. Give up and go down the pub.

Sometimes the last suggestion can prove less taxing. But assuming you're hellbent on making your life complicated then to obtain measurements I use the following equipment and techniques-



Most items should be fairly familiar. We have a profile gauge, a reel of solder, a set of callipers, rule and a propelling pencil. You could get by without a set of callipers or a profile gauge, but they are useful sometimes and not expensive to purchase.

If you have access to a 3D scanner, then you don't need any help from me. However such a sophisticated tool isn't really required for building, especially if you will be makign a master using hand techniques.

One item not pictured, but the most important tool of all, is what Dave refers to as the MK 1 eyeball. Measurements can often be misleading, or errors can creep in, so if your gut tells you something isn't right, trust it.



The model master shown here should be familiar to any baby boomer, it’s the Yellow Submarine. I wanted to produce a model about 18” long, small enough to make it easily transportable, but big enough to fit RC equipment in.

I purchased a small plastic kit off ebay, which was reissued by AMT/Ertl in the late ‘90’s. I also purchased a DVD of Yellow Submarine to obtain some frame grabs of the film.

The AMT/Ertl kit featured a few inaccuracies, but they were very minor, and would be easily corrected.

As the kits hull comes in two halves, obtain a keel outline would be straightforward, and I merely used one hull half as a template and traced a line around it as shown-





I then required loftings at intervals along the keel. These give the cross sectional outline of the boat. I find it’s a good idea to either use natural markings on the boat to mark points at which you will take a profile, and/or add additional marks with the aid of the propelling pencil. The outline can be taken using either a profile gauge, or some solder. The pictures paint a thousand words-





I find the solder works better for smaller models. Having taken a profile, you can then transfer this to paper. This technique can also work to obtain the keel outline if you’re unable to split the model in two like I did.



Once all the outlines have been taken, you can tidy them up, then either scan them into a computer, take them to a photocopier or scale them up using traditional draughtsman techniques. Here are my working drawings. A little rough and ready perhaps, but they were good enough to do the job. I printed these out at 200% and transferred them to a sheet of plywood.



Further reference and measurement can be made by taking shots with a rule up against the model, like so-





Andy

[steveneill]

You could wax it up

You could wax it up inside and release it so that you can slosh in some Alumilite and remove it barring there's no under cuts or negative draft BD.

Then pull that out and cut it up.

The other crude way would be to build up little pieces of card board and glue at the cross sections you want gradually building up the contours. Then clean it up. I have done this before and it works. Both in fact.

Steve

P.S. Another way is to cast in a flexible polyfoam. That will allow you the under cuts and still be able to remove it. That works too. Burman Industries carries it.

[davinci]

Do you have access to

Do you have access to the interior of the hull, or most of it?

If so, then cutting cardboard templets to fit inside hull, is one way.
In areas with less access, modeling-clay or putty or similar material could be pushed in to get shape of half hull (from keel to gunnel).

If not, making templets from cardboard or clay on Outside of hull could be done and then corrected (reduced) for difference in inside and outside of hull.

[scott t]

How about using a laser

How about using a laser level to project hull sections on the side then
photograph from the bow on (or stern) position. If the hull and camera stay
stationary and you move the laser down the hull to each station and
take a photo. Then scale the photos up or down and print out and
cut out as patterns.

Never tried it so not sure it will work. Just thought of it from seeing
people using laser level lights to mark straight lines on there hulls.

Scott

[bigdave]

Thanks for all the great

Thanks for all the great suggestions guys.
Some great ideas.
Scott
I will have to read yours a few times.
Not sure I get your drift. BD.

[bigdave]

BTW- I case anyone was

BTW- I case anyone was woundering.

[scott t]

Here you see a laser

Here you see a laser shining on a model. Good for drawing straight
on a curve. Here is the web site these photos belong to.http://www.propellor.tv/SAS%20fuselage%201.html


If this is what it looks like from the side view what do you think it will look like from an end view? Maybe a hull section.
Now if it apears as a hull section to the eye maybe it can be photographed.
Then print it out and start enlarging the image with a computer printer or copier.

There was a image here on SC showing someone working on the nose contour of there sub trying to make it symetrical using a laser
line to see the difference side to side but I have not located it yet.

Scott

[bigdave]

Interesting concept. I see what

Interesting concept. I see what you mean now.
From an end view any point less than the widest point of the hull would show the laser line.
Not sure if it would work in the real world, but it is worth a try sometime. Thanks, BD.

[Guest]

Re: Yellow Submarine

I would love to build a diving Yellow Submarine if someone offered a fiberglass model that was over 54" in length.

Mine is a bit small for you then at about 19".

But why so big? A 54" hull would be a very chunky proposition indeed,and would pose quite a challenge to find a suitable venue to sail in, as it would be over 30" in height from the base to the tallest periscope, assuming your using the AMT/Ertl kit as a reference.

My own preference is to aim for a model which can fit comfortably in the back of a car AND is around a foot in height or under.

Models this size are easy to transport and can be sailed in most ponds and lakes.[/quote]