"Ghost line" queery... any ideas?

[Wild Dingo]

Recently I recieved the plans for Sørkust from Anita... Sørkust was designed by her father Al Mason in 1939... much along the lines of the lovely Elly who we all love and admire...

Anyway after much queery and frustration I now come to the esteemed company here at woodenboat for your imput...

The plans have within them as you can see by the following pics what Al has called a "ghost line" located in the same place as the "profile line" in the profile drawing... and stands away from the keel line in the diagonals drawing...

The Diagonal drawing you can see how it angles up along parrelel to the rabbit... ooopps sorry Dave... RABBET line... but stops at the Diagonal F and 18" below the waterline marks...

http://www.imagestation.com/picture/sraid32/p0616acb48669c917b1c7d2750e230bb9/fd431990.jpg

And the Profile drawing it follows the profile and keel line...

http://www.imagestation.com/picture/sraid32/p07ef72a04b37c76abb1eb73a87f77865/fd43198f.jpg

Now the problem is that no one seems to know what a "ghost line" is... I have spoken by email with Anita who initially thought it had something to do with the info needed for the foundry when laying the keel but was unsure so she has suggested I post my question here... She then researched it some and found that...

Anita Mason's Email
"What is most telling is that when the OSTKUST design {Ostkust was Sørkust's big sister ~} was reprinted in an
issue of "How to Build Twenty Boats" by Fawcett publication, the plans
were redrawn and the text was typeset. On the lines drawing this time,
the only word used was "Profile" on the Profile and Plan drawings. On
the Body Plan, the "ghost" line appears but is not labelled. My conclusion is that the term "ghost" line is simply an archaic word Al
used on his early designs"Comment in { } are mine from another area of Anita's email and rather than just copy and paste the entire email I thought to use just that which relates most directly to this "ghost line" matter...

Is it really this simple?? And if so then why didnt other designers of Als era also use the term? I have never seen it referred to in any of the older designs Ive seen in Rudder or other info Ive garnered... why would Al use an archaic term when no one else was using the term? this would no doubt cause difficulties for any builder if one designer uses an archaic term for something no one else uses?... Im not having a go in any way at Al as Anita is aware but it seems strange at least to me to have a term that no one knows the meaning of on his designs...

I have also spoken by email with Dave Fleming who has never heard of a "Ghost line" and nor have Bernadette and David Hedger who I have also had contact with regarding it...

So I come to you fellas and sheilas in the hope someone here can shine a tad of light on this interesting "line" conundrum that I find myself with...

Does anyone have any idea what the "ghost line" is meant to be for? Am I being over cautious? Is it really necessary for me to know just what this particular line was referrencing? If its there then surely its purpose should be known? Surely someone knows its purpose!!...

I am a curious buggar and now I simply HAVE to know why Al would put this "ghost line" in his drawing if no one knows what the heck he was meaning to say!!

Thanks to all...

Take it easy
Shane

[ 09-18-2002, 05:12 AM: Message edited by: Wild Dingo ]

[Seth Wood]

Check Buehler's book. I think the ghost line, along with the rabbet and bearding lines, defines the square shape of the planking as it hits the keel, in cross section.

That is, picture a cross-section of the inboard edge of the planking. It forms kind of a diagonal, three-sided rectangle cutting into the backbone. I don't have the diagram in front of me, but I think the top corner is the rabbet, the bottom corner is the ghost line, and the bearding line is inside?

Cripes, I may have made things more confusing, not less. Well, go easy; let's not confuse enthusiasm with knowledge! Suffice it to say I have heard of the ghost line....

...Oops, taking a second look at the lower image, it looks like the ghost line along the bottom of the lead is nowhere near the rabbet. Confusion ahoy...

[ 09-18-2002, 10:18 AM: Message edited by: Seth Wood ]

[Wild Dingo]

Originally posted by Seth Wood:
Check Buehler's book. I think the ghost line, along with the rabbet and bearding lines, defines the square shape of the planking as it hits the keel, in cross section.

I don't have the diagram in front of me, but I think the top corner is the rabbet, the bottom corner is the ghost line, and the bearding line is inside?

Suffice it to say I have heard of the ghost line....

...Oops, taking a second look at the lower image, it looks like the ghost line along the bottom of the lead is nowhere near the rabbet. Confusion ahoy...Yep... thats where it all goes legless!!... actually Dave said those three lines were known at least to him as 1)Rabbet line 2) Bearding line and 3) middle line... and when looking at the plans the only line named is the rabbet line so I guess its work I have to do to find the other two! yes!! love that work gotta be positive :rolleyes: ... oh and the said problematic "ghost line"

Thanks Seth means people have seen it and are thinking about it!! :cool:

Take it easy
Shane

[Matt Middleton]

I'm still trying to picture the "diagonal, three-sided rectangle" :confused: ;)

[John E Hardiman]

Lets set the word "ghost" aside for a moment and look at the line and plans.
The line appears to show the "square siding" of the forefoot and keel. Notice that it also appears to extend back only to the heel of the lead keel. I'll bet that the radiuses of the forefoot/keel section ellipses are not given and the lead keel is specified as a given weight.
Given the fact that it is nearly impossible to show the true shape of the transition between the spoon bow and the full keel forefoot in two dimensions due to the sometimes extreme hollow as the "canoe hull" rolls away from the stem, many times you will just put in "construction lines" and allow the builder to fair in the shape on the stocks. This is similar to drawing in frames past the transom or extending them above the sheer in order to pick up the true shape of the curve in three dimensions. Now with the lines given the builder could set up the forefoot,keel,and deadwood; properly sided but unfaired. Next a plug for the keel would be made, with the proper shape/tangents at the lead/keel/deadwood interface and a fair bottom shape to give the desired weight. The keel would be cast(while planking up continued) and fitted up before the forefoot would be shaped to match and faired to give good waterlines, buttocks, and diagonals.

Anyway, as I see the plans there is more than enough information to build the boat regardless of what the line is called. I have heard lines in the plans that are needed for layout, but cannot be physically touched called "ghost", "phantom", "construction", "layout", "building", etc. In modern submarine construction there is the mythical "main axis" which everything in the plans is measured from but can never be measured to in construction. ;)

[Donn]

John has it right. A "ghost line" is a reference line used for a variety of purposes, most commonly maintaining parallels in a grid. You'll find it's a tool in most CAD/CAM software.

Here's a reference to it in an article about designing a ferrocement hull:

"Stem construction

The initial stem rod of 16 mm dia. will be bent to the stem pattern prepared previously (ref. 2.10) making a 12 mm allowance for the skin outside the stem rod. In this case the rabbet line follows all the way up the stem (as opposed to a ghost line sometimes used by designers). "

"Alternatively, if the rabbet line is designed as a ghost line and additional stem strength is required, this can be achieved by creating a web down the stem's length or by making an artificial inner surface to create a triangular reinforced section."

http://www.fao.org/DOCREP/003/V9468E/v9468e09.htm

[WRB]

Shane,
the other fellas have it right, there are a couple of "ghost" lines on the Jan plans, but, as they are not labeled in anyway, their meaning becomes obvious. Imagine, if he had not labeled it, it looks like the bottom of the keel squared off, and thats exactly what it is.

cheers
waz

[TR]

It's the intersection of the section and the half-siding of the bottom of the keel, before rounding! Ghost Lines also appear outside a rounded stem, again they are the intersection of long lines (waterlines) with half-sidings before rounding. They are a fairing aid and give you someplace to run the batten to.

All the best, Tad.

[Dave Fleming]

AS they say, it's a bad day when you don't learn something new!

I just spent some time looking at several sets of plans I have from several different sources both Wood , Aluminum and Steel and there is no reference to 'ghost lines' but, I do see how it works in that design. To the best of the collective knowledge, is that term still used or ????.

[Donn]

I asked the Bonnaker about them this afternoon. He reminded me that when he measured the pilothouse top for the new hatch, he lightly drove two small brads into each end of the joist (he calls them columns) of the ceiling, and stretched a line between them. He then measured from that line. He say's that's a ghost line. He has this little parable about the uselessness of a level on a boat.

[Dave Fleming]

Joist as in port to starboard beams?

[Donn]

Originally posted by Dave Fleming:
Joist as in port to starboard beams?Actually, on this coast, they run starboard to port. But yes...they be beams.

[TR]

Dave;

" is that term still used or ????."

Perhaps it's an East Coast term. Perhaps it comes from the Sparkman & Stephens office? I note offsets for a ghost line in Francis Kinney's table in Skene's Elements. I know I was including ghost line offsets on tables 10 years ago. But almost no one is drawing lines by hand anymore, certainly not at a professional level. And consequently almost no one is lofting by hand at a professional level.

It amazes me how quickly this stuff disappears. I have a vision of myself sitting in a museum in twenty years with a collection of splines and ducks trying to explain that you can do this without a computer!

All the best.

Tad

[Dave Fleming]

TR, last design office/loft I worked in circa 1989 did most drawings bye hand, shipped them out to be digitized, then converted to 10th Scale for old DEC machine, made ***paper tape*** for plasma burner and we still had to loft many an item on the floor for patterns for the bending shop or out side fitters!

I acutally bought a copy of RHINO to fool around with but for this old faht the learning curve was too steep and I went back to doodling with my K&E ducks and splines and Copenhagen curves. smile.gif

[ 09-19-2002, 04:55 PM: Message edited by: Dave Fleming ]

[TR]

Dave;


Yes, exactly, computer design does not speed things up much but it does redirect the work. Though the design can be done in the computer, we still need to convert design files to cutter or burning files. Usually the poor builder has nothing to work from but a body plan, which makes things difficult.

Rhino is a great program, but not that great for drawing hull lines. You can draw a boat in it quite quickly, but it won't be very fair. I don't know a great deal about it but it seems to me that the battens are too floppy. I like multisurf for hull lines/surfaces much better but it is much more difficult to work with than rhino.

To draw a boat in rhino I start with the profile, just as you would on a piece of paper. Start in the "Front" view box. Start at the top of the stem and draw the stem and forefoot in one line with about 5 points. End it underwater at about station #1. Draw the sheer in profile starting with a "snap" to the top of the stem. Only worry about how it looks in one view at a time.

Draw the sheer with about 4-6 points to the top of the transom. Do the same for the profile/bottom centerline. Again "snap" to the bottom of the stem. Run the bottom centerline back to the bottom of where the transom will be.

Now go to the "Top" view. What you've drawn so far are a couple of straight lines. Select the sheer and hit the "show points" button. Pull on the points to get the deck line in plan view. Now you need some sections. Depending on the size of the boat you want three or four section shapes. The first will be the transom. In the "Top view" snap a line from the end of the sheer to the bottom centerline end. Then rebuild that line with 5 points, do this in "curve, edit tools, rebuild".

In the "right" view box you see a straight line from sheer to centerline. Select the line, show points, and pull it out into your transom shape. Go through another couple of curves like this. First draw the straight line in the top view and the pull it into shape in the right view. You need one section amidships and another forward.

Then you are ready to put a surface on this shape.
In "surface" select "sweep 2 rails". In your model select the sheer and bottom centerline as your rails. Then select your section lines as the "cross section curves", work from stern to your stem line. Hit enter and you have a surface.

There’s a lot more but you have a hull you can look at and adjust to your hearts content. If you are doing a vee-bottom just substitute the chine for the bottom centerline and make two surfaces.

Have fun!

Tad

[Dave Fleming]

TR, guess I will 'activate' that copy of Rhino 2 and use your tutorial for a bit.
Thanks for posting it.
dave

[tony morales]

I also wanted to know the use of a ghost line on plans as there one on my drawing plans and offset table, so I went to the source. I questioned Olin Stephens and his response is as follows " As to the ghost line, I think such lines can be used in different ways and as points used in fairing to any points on a drawing that don't exist on the hull or whatever. Typically along the forebody or stem profile the material stem is snubbed, often to an expanding face or radius upward from the waterline."

[Thad]

Good for Olin!!! Sounds right.

[paladin]

yup..they is lines to show what things would look like if the originating line point is continued or extended in a straight line...fer reference only...

[tony morales]

Also used as a reference line in three dimensions. Take the z (ghost line) axis,look at it on point, let x and y axises be bisected by a 45 deg angle through the origin,and let a distance "A" along the 45 deg line define the distance from the z axiz to the curve of the tangents at each station. Dimension A is listed in my table of offsets this way.