Scaling a linesplan on computer (Mermaid Sailing Canoe, FREE!Ship/DELFTship)

[Bruce Taylor]

In another thread, Robmill0605 asked about methods for making up a set of plans from an old lines drawing with no offsets. I mentioned that I use FREE!ship / DELFTship to do the job, and he expressed an interest in a quick tutorial.

There are many ways to resurrect an old linesplan, of course, and each has its advantages. It can be done on the drafting table, with dividers and a scale rule; and any decent CAD program can be used to line up splined curves against a background drawing.

I'm partial to FREE!ship / DELFTship for three reasons. First, it's extremely quick. I find I can take a linesplan to a finished model in less than half an hour (although, if I want to, I can spend much longer fairing and fine-tuning, afterwards). Secondly, in addition to drawing up the lines & providing offsets, it renders the hull as a 3D model that can be inspected from all angles, or exported to full-featured 3D rendering program like Rhino or Blender. Lastly, various versions of the program are available a low cost (or no cost at all).

In the examples below, I'm using DELFTship Pro, but most of the procedures I describe are nearly identical on FREE!ship 2.6 (the last stable version of FREE!ship produced by the original developer, Martijn Van Engeland). A free version DELFTship (with some features disabled) is available here: http://www.delftship.net/ . FREE!ship 2.6 is available here: http://www.softpedia.com/get/Science-CAD/Freeship.shtml

I'll use the Mermaid sailing canoe as an example, because (as far as I know) the lines are available but the offsets are not.

The Mermaid sailing canoe was something of a legend, in her day. She was designed in 1913, for the express purpose of defeating the Canadian Ralph Britton, who had won every event in 1912. Leo Friede of New York asked W. F. Stevens to design a racing canoe that could beat Britton.

As F. H. Froling put it in 1921:

Stevens found no easy task before him, but his genius asserted itself, and the result was the "Mermaid," a perfect creation from the viewpoint of naval architecture. In the trial races, to the astonishment of all, the "Mermaid" outsailed a fleet of the fastest canoes of the American Canoe Association.

Friede's Mermaid remained a formidable competitor for the next two decades, giving Uffa Fox's Valiant / East Anglian stiff competition for the American canoe championship of 1934.



Mermaid's lines were reproduced in Schoette's Sailing Craft (Macmillan, 1937), as follows:

[Bruce Taylor]

First, I scan the original, and use the freeware image viewer Irfan view to crop out the various views.

Bodyplan:



Plan view:



Profile:

[Bruce Taylor]

Next, I run DELFTship and select File --> New.

The only dimension I have for Mermaid is her length. She is 16' long.

In the dialogue box, I enter 16 as the length, and set the units as "feet." I don't worry about entering a value for the beam, at this point (she'll be around 30", presumably, but it doesn't matter right now). I put in an arbitrary number for draught: half a foot.



Then I go to the "profile view" window in DELFTship, click on the right mouse button and select Background Image --> Load, and load in the cropped jpeg file for the lines profile view:



The background image is the wrong size and in the wrong place, but this is easily fixed.

I click on the right mouse button, and select Background Image --> Origin. Then I click my mouse over the background image and drag it over so that the transom lines up with the transom on the DELFTship model, and the LWL shown on the linesplan lines up with the arbitrarily chosen load waterline on the DELFTship model.

The background image is still the wrong size, but is in the right place:

[Bruce Taylor]

Now, I have to scale the drawing so that it is (in DELFTship's little world), 16 feet long.

I click on the right mouse button again, and select Background Image --> Set Scale. A set of crosshairs appears, and I position those over the stem rabbet shown on the lines drawing (which I know to be 16' from the rabbet at the stern post).

A dialogue box pops up, with two coordinates. The first coordinate shows the X (longitudinal) position of my crosshairs; the second shows the Z (vertical) position.



The X coordinate is set to 15.2703...a little short of what I want.

I ignore the Z coordinate (DELFTship will take care of it automatically) and set the X coordinate to 16.



The background image is now 16 feet long, and lined up, fore and aft, with the DELFTship model on screen.

[Bruce Taylor]

The visual clutter is a little hard on my eyes, so I use the "blending" tool to mute the papery white of the background image a bit, so that it blends in with the DELFTship background. I want to be able to see the background image, but I don't want it to interfere with my view of DELFTship's control points & mesh lines:



Now, I start dragging the DELFTship model into alignment with the background image. I grab points on the control mesh and pull them into new positions:



I want the profile of the boat to be approximately the same as the profile in the background image (although, at this point I won't be too careful...I'm just roughing in the shape):

[Bruce Taylor]

Now, I move over to the Bodyplan window to see how things look from the front and back.

As you might expect, it's all wrong.

For one thing, the boat in our model still has a transom. And the bilges are far slacker than they should be.



Also, there are too many stations (those turquoise curves). The first thing I do is get rid of those. The linesplan seems to show seven stations positioned at two-foot intervals. I bring up DELFTship's intersections dialogue (View --> Intersections) and select the Stations icon:



I delete the old stations, and instruct DELFTship to enter new ones at 2-foot intervals:



And I now have the same number of stations as the original lines drawing:

[Bruce Taylor]

Now, I load a background image of the bodyplan, just as I did earlier for the profile:



This time, the background image is hugely oversized. I center it on the centerline, and drag it down so that the lowest point of the keel in the background image lines up with the low point of the keel on my model (right click, Background Image -- > Origin).

Now I need to set the scale. Having already created a profile drawing, I know the actual height of the sheer where it meets the stem (a bit more than 1.3 feet). I bring up the "Set Scale" dialogue (right click, Background Image --> Set Scale) and enter the proper Z coordinate (1.3182 feet). The image is automatically scaled to the correct size:



I can now concentrate on pushing my control points around in the bodyplan, until the station curves on my model line up with the station curves on the background image. I rough it in, and refine it later.

[Bruce Taylor]

I repeat the same procedure for the plan view:



Then, I go back to each of the views in turn, refining the lines and fairing the hull.

Next, load a background image for the sail plan, if wanted:



Tidy it up, and we're done:

[PaulC]

Wow, very thorough job and a very nice presentation. That sure took a few minutes to put together.

It seems that there was also a method for taking a table of offsets into Freeship (via an Excel file???) that I thought I had saved. I have done a bit of searching but have yet to find it. Do you recall how that is done?

[Ahimsakid]

Thanks Bruce, nice post!

[Don Z.]

Wow, very thorough job and a very nice presentation. That sure took a few minutes to put together.

It seems that there was also a method for taking a table of offsets into Freeship (via an Excel file???) that I thought I had saved. I have done a bit of searching but have yet to find it. Do you recall how that is done?

Somewhere, I have the pdf on how to do this. PM me an email and I can send it to you...

This is something that needs a little help though. I used it to enter the offsets for Fame. Where it seemed to stumble was on the transom and the tumblehome. Things got wonky there, and I struggled to get the control points dragged appropriately. I'm sure it's a lack of experience thing. That said, I was pleased that the displacement measurement that DeftShip spit out was reasonably close to my pen and paper calculations. Way faster though...

[Bruce Taylor]

It seems that there was also a method for taking a table of offsets into Freeship (via an Excel file???) that I thought I had saved.

You're probably thinking of the one Bryan Hansel posted on Canadian Canoe Routes, shortly after FREE!ship first appeared: http://www.myccr.com/SectionForums/v...f3c5bc38155319 It used to be on Martijn's website, in the tutorials section.

I see Bryan has reposted it as a blog, now: http://www.nessmuking.com/articles/n...sing-freeship/

[Woxbox]

Tidy it up, and we're done:

Very nice demonstration. But perhaps a bit of understatement at the end here. My experience with Delftship is that when you get to the "tidy up" part, you're about half-way done.

I do find the most tedious part with the program is typing in all the xyz coordinates. A shortcut would be nice to have.

[Antonio Majer]

Just to show you a slightly different method. Some years ago Bruce Taylor "convinced" me too to use freeship, and now I'm another addicted to it .
---
I'm trying to build the famous Dark Harbor 12.5, similar to that one of Art Read; I bought the plans with WB store. Since the original drawings by Crowninshield & Burbank are extremely accurate, I imported the scan of the stations lines into my Autocad, and I dimensioned some points of them via the Ordinate Dimension command (here below you see a mess, but actually the dimensions of every line lie in their proper layer)



Then I compiled these dimensions in an ASCII file, as described by the manual (here you see the beginning and the end of the same file)



...and I imported it into freeship (surface command), getting the hull (there were still some spots to correct) :



Anyway here after the correction and having drawn the fin and the transom:



(now I have imported the hull in autocad, with the intention of drawing everyting carfully. I hope to start building this spring).

[Bruce Taylor]

VMy experience with Delftship is that when you get to the "tidy up" part, you're about half-way done.

But that's the fun part.

Antonio, that's pretty impressive. If I were scaling up a linesplan for use in a large, time-consuming build I'd certainly do something similar.

It's worth pointing out that the quick n' dirty approach I show can't be expected to produce a perfectly accurate version of the original. But then, assuming the offsets really are lost, there ain't no original to compare it to! Mermaid herself is in a museum collection, somewhere (Mystic, maybe?), but will have changed shape quite a bit, over the years, so taking off the lines from her hull would probably introduce a few errors.

There are various ways inaccuracies can creep in, when working from scanned drawings. Scanners will tend to introduce some parallax error, I think. Also, the scans have to be dead level, or the method won't work at all (perhaps photoshop, or something similar, can be used to correct scans that are slightly off-level...I dunno). And, when the various views disagree it's necessary to make judicious choices and adjustments, here and there (as you do when lofting). Still, if it's done intelligently, I think the method can be used to produce a fair approximation (perhaps "adaptation" is a better word) of a historic hull.

[mcdenny]

Bruce, Thanks for putting all that effort into your excellent tutorial. I muddle around in Freeship a bit and never thought to use the background image for anything. What a great idea.

[John Meachen]

Thanks for the thread Bruce.I have a neglected project of an O-Jolle half model to complete and I wish I had been aware of the possibility of doing it this way.While it remains a bit too chilly to get outside and carve wood I might usefully go through the necessary steps to learn your system.

[Spokaloo]

Bruce, this was very timely. Just spent the afternoon getting a tolman skiff all drawn up.

Now about the way to make her hard chined......

E

[PaulC]

Got it, thanks!

[Bruce Taylor]

Bump, for Rob.

[Robmill0605]

Bump, for Rob.

THANKS!!!! You are the man!

I have a lot to learn here Bruce. I just downloaded Freeship and am playing with it trying to learn this.
perhaps a few painfully obvious questions;

I did not realize that Delfship is another program, what's the difference, and do I need both?

How do you scan a jpg into Freeship?

How do you put existing offsets into the program?

Where does it generate the Table of Offsets?

I find this entire thread very interesting because I'm constantly lofting dream designs, and it will be fun to do this with ones that I do not have offsets for, or none exist.

[Bruce Taylor]

I did not realize that Delfship is another program, what's the difference, and do I need both?

FREE!ship was the original name of the program. It was licensed under GPL as Open Source Software, which means anybody can use it, or adapt the code, provided they follow GPL guidelines. Martijn van Engeland spent a couple of years developing the software, then decided to take it commercial. He quit his job at the University of Delft, changed the name of the program to DELFTship, and added a huge assortment of new features (mostly as independent modules that can be purchased separately). The core of the program, DELFTship Pro, is quite reasonably priced, as these things go. It's also available in a "Free" version, but this has certain features disabled (printing, for instance).

The last stable version of FREE!ship was v. 2.6. It contains most of the features available in the of DELFTship itself, and includes a few features that later got removed from the "core" program and placed in separate modules (cross curves, for instance).

How do you scan a jpg into Freeship?

Should be pretty much the same procedure as shown above. Just scan your files, save them as jpegs, and crop them as you please. Then right click, Background Image --> Load.

How do you put existing offsets into the program?

FREE!ship / DELFTship can import an ASCII table of offsets, but these have to be expressed in a certain format (X,Y,Z coordinates, where X gives the location on the longitudinal axis, Y tells how far out from the centerline a point is, and Z tells how far up it is from the baseline). Converting from the old format (feet-inches-eighths) is tedious, if you do it by hand. Bryan Hansel wrote a spreadsheet to do the job (should be available through the link given above).

Where does it generate the Table 7of Offsets?

File --> Export brings up a range of options.

[Robmill0605]

Just awesome, I'll get busy learning this.
Thanks so much.

[Bruce Taylor]

I'll get busy learning this.

As I mentioned in the other thread, it can be baffling, at first, especially if you've never used a control mesh to model a hull. I struggled with the program for nearly a week before I realized that the coordinates of the control points do not correspond to any actual coordinates on the curves of the hull itself. I kept thinking the control points were the same as the offset coordinates through which we draw our splined curves, when lofting (my previous use of splines in 2D CAD only confused me further).

Anyway...if it takes a while to get going, don't be discouraged.

[boatbear]

Bruce, that is an excellent tutorial. Thanks for posting.

[TR]

In a wonderful example of how open source works, FreeShip Plus is now available for free download here http://freeship-plus.pisem.su/downloadsE.html

This is the original Freeship updated and further improved by a fellow named Victor T. I think he's up to version 3.04 now. I've been running 3.01+ for a while with no problems and many additional features over Freeship.

[WX]

I had a thread going just recenty on FREEship...yours is far and away superior..in that you know how to use the app. Thanks.

[PeterSibley]

I've just found this , very applicable to my current headache .Thanks Bruce .

[Captain Blight]

Bruce,

I recently uninstalled 3.0 to free up some room on my old ENIAC unit. I picked up a newer, better laptop and am considering reinstalling Free!ship again. So here's my question:


Without getting into the ins and outs of NURBS-based surface modeling programs, how useful do you think Free!ship would be in extrapolating and modeling other shapes than boats? Do you think your technique as described above would work for anything I could get a three-view drawing of?