Table of offsets – Import/Export

[John Owles]

Has any body managed to use the import/export of Offsets facility in Delftship?

My business (see http://www.rovcom.co.uk) specialises in the restoration of old wooden vessels which range from 14ft fishing boats through classic yachts to 34m German Schnellboot from WW2. Often the work entails producing lines plans either at the start or upon completion.

I noticed that Delftship has the facility to import Offsets so I downloaded a copy. Having studied the manual I tried importing Offsets from a 1912 30ft gaff rigged dayboat that we are about to work on.

Having taken the lines, I imported them to see what happens. A mess! At first I thought that I had set up the txt file wrong but on checking the offsets should be readable and OK for fairing.

When imported some stations and water lines were discarded. I assumed that there must be a restriction within the free version, although this is not mentioned.

Out of interest I just downloaded Classic 51 from the database, opened it, exported the offets and then imported them. Total mess, the program played exactly the same game. Nothing at all like the original with station lines and waterlines going everywhere.

If you export any offsets and then import them again they change each time so I think something is not at all correct here.

All a bit tricky if you need to archive a bit of history.

Any ideas?

John

[Marven]

Is it possible for you to post the file with offsets here, or is it classified?

[John Owles]

Nothing classified, just a rather beautiful old gaff rigged day boat from around 1912.

The units are imperial feet.

I have no doubt I have probably done something daft or not done something that I should have done. Anyway see what you think. Any help will be very much appreciated. [file name=Halcyon1912.txt size=1147]http://www.delftship.net/delftship/media/kunena/attachments/legacy/files/Halcyon1912.txt[/file]

Attachments:

• Halcyon1912.txt

[Marven]

This is actually the preferred way of doing it, since you have more influence on the placement of control points. Usually I take as few control points as possible, then first model the deck line and profile so it matches your design. Once this is done start modeling the frames aft to front. Once you’ve done the frontmost station you’ll notice the aft station has probably changed sit the shape is not correct anymore. In this case repeat the process until you’re satisfied. If you fond that in some case you can’t get the shape right, you’ll probably need to insert some additional control points.

Your model had quite a few irregular poins. I’ve inserted some new points to make the control net regular again and also to have a better control over the shape in some areas. I’ve faired it a bit and it seems better now. I gues it took about 10 or 15 minutes. [file name=miller_xyz_modified.fbm size=33737]http://www.delftship.net/delftship/media/kunena/attachments/legacy/files/miller_xyz_modified.fbm[/file]

Attachments:

• miller_xyz_modified.fbm

[Marven]

Yes. You can view those with the inclined hydrostatics extension.

[John Owles]

I’m afraid that you have lost me now, or perhaps I was never found! I am not sure how to import the control points from the offsets that I have taken off the boat.

Also, I don’t understand how you can export the offsets from a perfectly fair hull such as the Classic 51 which, when subsequently imported do not produce the same model. Doesn’t seem to make any logical sense to me.

Still Confused

John

[Marven]

John,

Basically there are two ways to recreate an existing design:

1. By importing offsets from an offsets table, or a similar file format. In this case the software will create a surface that approximates the given points as closely as possible. To obtain the best fit of the surface the generated control points may be scattered, which is not very intuitive to work with. In almost any case it still requires additional manual fairing and stitching, depending on the shape of your ship and the number of points in your offsets table.
2. An alternative way which requires slightly more work but gives better results in almost any case is to use markers or an image as a background reference. You can start a new design and model it to fit your reference lines, as described in my previous post. Personally I prefer this over importing offsets since the distribution of controlpoints is in your own hand which makes it easier to fair the surface.

To better understand the problem of exporting/importing offsets you need to consider the fact that offsets or generated only at the intersection of waterlines and stations. A lot of crucial information, such as the shape of your keelline, the startpoint and endpoint of waterlines cannot be specified according this format, so by importing an offsets table a lot of information is lost.

Now in the old days this wasn’t really a problem since the loftsman would fill in the gaps. A computer system in most cases misses the intelligence to do this in an estethically pleasing way, and it also has the disadvantage that the surface must comply with the mathemathics behind it.

The second method above overcomes these problems, but it requires slightly more work.

[Jeffry Fontaine]

I am experiencing some problems with the importation of the data as a text file for the hull lines and offsets function.

I have the information saved as the attached MS Word.doc file and my question is what am I looking at in this document?

I can decypher some of the data but the groupings of numbers have me a bit stumped as to what values they are supposed to represent. Can anyone assist me with this problem. I am trying to create the Nasty/Tjeld class FPB hull and up till now my previous attempts have not been what I had expected.

Is the data in the document that appears as numbers separated by a “-” supposed to represent Feet, Inches, and Fractions of an Inch? Or some other values? By trial and error I have found that the “+” must also be removed even though that represents a fraction of 1/16th of an inch. How do I address this measurement if the symbol is removed?

I would really like to get this as close as possible to what the original designer had created.

Thanks in advance for any assistance you can provide,

Jeffry Fontaine
Bremerton, Washington

[file name=Nasty_and_Tjeld_Class_Lines_and_Offsets.doc size=137728]http://www.delftship.net/delftship/media/kunena/attachments/legacy/files/Nasty_and_Tjeld_Class_Lines_and_Offsets.doc[/file]

Attachments:

• Nasty_and_Tjeld_Class_Lines_and_Offsets.doc
• Tjeld_and_Nasty_Class_Hull_Project__created_with_DELFTShip__005.png

[Marven]

The second line on the first page says:

Table of Offsets (to outside of planking) in Feet, Inches, and Eighths “+” indicates an additional 1/16.

I think there’s your first answer. If the additional Plus is not there, then treat it as zero, otherwise simply add anothe 16th of an inch.

[Jeffry Fontaine]

So the data displayed as number – number- number in each of the columns represents the x – y – z coordinates of each frame.

It looks as if I need to try and manually create this list of offsets from the spreadsheet. I am experiencing some problems with the spacing on the text file. How many spaces are required between columns to physically separate them as you read down.

Sorry to keep pressing the subject with silly questions but I thought it would be a simple conversion by copying the data to a text file and importing it to the DELFTship program. So far it (DELFTship] refuses to recognize the text file as a table of offsets. I even attempted to modify an exported table of offsets with the data and import it and the results went terribly awry when the hull appeared on the screen with a definite boomerang shape to it which was not very boat-like at all.

[Warren Smith]

Since the last post to this thread is over a year ago, I’m not sure anyone is still posting…But if you are.

A couple of questions.

1. I have looked over the docs and sample offsets table description but don’t find how one describes the flat of bottom. All the examples have a 0 for that line – indicating the flat of bottom is not described in the offsets file. So where does the flat of bottom go.

2. I have also seen issues with the offsets table import and export. If I import an offset table (a good one) it comes in just fine. If I then export that offset table, it seems to export ok (that is the correct format but not necessarily the offsets themselves). But if I import that exported offsets, the body, plan, and profile are all messed up.

what gives.

[Warren Smith]

Also, I meant to ask in my last post how to deal with Feet vs metric when importing table of offsets.

When you import table of offsets it starts a new project and it automatically reverts to metric, yet the table of offsets in in feet and fractions of feet.

It is simply a matter of changing the project defaults once you have imported the data? That doesn’t seem to work for me.

[Anji Reddy D]

Hi

I am facing problems to preapre offset table format for DELFtShip with Flat Keel. Pls provide any Sample file.

[Author]

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