# Thread: How to take Take Hull Lines off an existing boat?

1. Gareth
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## Re: How to take Take Hull Lines off an existing boat?

A cheap and cheerful way to do it, is to take 3 strand household wire, that's known as "Romex" here in the States. Lay it up against the hull at intervals and photograph it. You would need to establish a datum line.

I'm not recommending this, I think it should be done together with the string and level method. If you draw the Romex method first, it will give you a perspective, while you're doing the accurate way.

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## Re: How to take Take Hull Lines off an existing boat?

All this talk about catenary and the practical requirement of getting a wire horizontal frame erected on one side of the hull , gets me thinking that two wires are needed, in order to balance out the tension of each other.
Using a rough lumber frame to start with, it becomes the compression member, between wires stretched straight and taught both above and below it.
Let us say that the lower wire will be configured to be the level ground( set up using a spirit level), and the upper wire the waterline.
Then a laser level can be used on a calibrated and moveable, height adjustable tower, to do all other horizontal measurements, being set to this wire frame, which is stationed at a set distance from plumb bobs at stern and bow centres.
Last edited by Lugalong; 10-11-2018 at 02:56 PM.

3. ## Re: How to take Take Hull Lines off an existing boat?

Youse guys are making this way too complicated.

4. ## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by Lugalong
All this talk about catenary and the practical requirement of getting a wire horizontal frame erected on one side of the hull , gets me thinking that two wires are needed, in order to balance out the tension of each other.
Using a rough lumber frame to start with, it becomes the compression member, between wires stretched straight and taught both above and below it.
Let us say that the lower wire will be configured to be the level ground( set up using a spirit level), and the upper wire the waterline.
Then a laser level can be used on a calibrated and moveable, height adjustable tower, to do all other horizontal measurements, being set to this wire frame, which is stationed at a set distance from plumb bobs at stern and bow centres.
If for what ever reason you cannot use a laser level, you only need one taught wire to create your ford and aft datum base line. You then need a straight edge just longer than your half breadth that can be set up level and square to your datum wire at every measuring station. You then use a plum bob and tape to pick up the waterline half breadths, and buttock heights.

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## Re: How to take Take Hull Lines off an existing boat?

The catenary/centenary thing is an artifact of stupid cell phones thinking they are smarter than the person using them, combined with awkward editing features.

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## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by Peerie Maa
If for what ever reason you cannot use a laser level, you only need one taught wire to create your ford and aft datum base line. You then need a straight edge just longer than your half breadth that can be set up level and square to your datum wire at every measuring station. You then use a plum bob and tape to pick up the waterline half breadths, and buttock heights.
Sure, its just that anchoring the ford and aft wire is maybe not that easy on a hardstand somewhere far away; say where pegs cannot be driven in or where hefty objects are not available.
In that case, a few 1x2's could be screwed into angle pieces that lie on the ground outwards ( to one side) from the keel line, and halfway up the vertical leg of these angle pieces, is the compression member between the wires equidistant above and below it.
After this, a straight edge, tape and plumb-bob will suffice to do the rest, as you say, Nick.

7. ## Re: How to take Take Hull Lines off an existing boat?

Too bad you guys are so far away from southern Nova Scotia. Next Tuesday I am going to be teaching a couple of guys how to take the lines off a 50-ft (15.25m) fishing boat using a much faster and simpler method than those being proposed in this thread. I expect to measure the entire hull in about six hours using two 1.5m-tall standards, four concrete builder's blocks, two small bottle screws, some welding wire, a ladder, an inexpensive carpenter's laser level, a plumb bob and a tape measure. Unfortunately, typing up the process is a bit long-ish, and I haven't had supper yet.

I think, sometime in the dark, distant past, the method I use was explained (with illustrations) in a thread on the WBF, but I can't remember in which department or the thread name. If I can find it, or reference to the method someplace else, I'll let you know.

8. ## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by mmd
Too bad you guys are so far away from southern Nova Scotia. Next Tuesday I am going to be teaching a couple of guys how to take the lines off a 50-ft (15.25m) fishing boat using a much faster and simpler method than those being proposed in this thread. I expect to measure the entire hull in about six hours using two 1.5m-tall standards, four concrete builder's blocks, two small bottle screws, some welding wire, a ladder, an inexpensive carpenter's laser level, a plumb bob and a tape measure. Unfortunately, typing up the process is a bit long-ish, and I haven't had supper yet.

I think, sometime in the dark, distant past, the method I use was explained (with illustrations) in a thread on the WBF, but I can't remember in which department or the thread name. If I can find it, or reference to the method someplace else, I'll let you know.
Be sure that you have got spare new batteries.
Jus' sayin.

9. ## Re: How to take Take Hull Lines off an existing boat?

Will have them for both the laser level and the camera, Nick.

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## Re: How to take Take Hull Lines off an existing boat?

There was a famous incident on Lake Union of a brand new 40-ish footer, probably in the 1960’s, wood, of a fairly conventional hard chine hull design. Famous designer, famous boatyard.
Well the boat floated on her lines and everything was great until it got up to cruising speed in the mid-teens, the boat heeled over to one side and would not come back to level athwartships. The yard tried everthing, the designer was frantically brought in, but nothing worked. The hull was eye sweet and fair above and below the waterline.
So the boat was hauled at Anchor Jensen’s, and Lloyd Johnson was called in. Lloyd was the pre-eminent lifts man, and he proceed to set up a lofting grid on both sides of the hull, using the ways carriage(which was probably at a slope of 6 degrees or so. From these station and waterlines(wires), he proceeded to measure the hull.
He found that one of the chines entered the water quite a bit forward of the other side, and said this was the cause of the listing at speed. After a bit of heated discussion as to who would pay, the Jensen crew filled in the chine that was further aft to match the other.
Turns out the Port steam framing crew got ahead of the starboard crew and the station molds were forced a bit out of level, with the principal result of the chine moving forward. I heard this part of the story while an apprentice at Vic Franck’s And we were building a 65’ motoryacht of Garden design, and I asked why there were steel rods coming from the station molds down to the shop floor? The shed was way too tall to brace the molds to the rafters, hence the rods to the floor. Why? To prevent the molds from being twisted during framing, and the above tale was given as the reason.
Boat was launched and sea trialed and performed perfectly.
There was a lot of money and reputation riding on that sea trial.
I heard this story in the ‘70’s when I was a yard boy at Jensen’s, and from Lloyd himself when he sold me my first chest of tools, which still has some homemade lofting tools that I cannot figure out how they work, I think they are for steel plate expansion, as Lloyd also happened to be the loftsman for the only battleship built on Puget Sound.

11. ## Re: How to take Take Hull Lines off an existing boat?

A Cross Line Laser gives you a vertical and horizontal line at the same time, so you no longer need the wire.

12. ## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by Paul Schweiss
which still has some homemade lofting tools that I cannot figure out how they work, I think they are for steel plate expansion, as Lloyd also happened to be the loftsman for the only battleship built on Puget Sound.
Can you post pictures? I would be interested and I expect MMMike would be as well.

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## Re: How to take Take Hull Lines off an existing boat?

Supposedly, besides the wire you don't even need a lines drawing, if the co ordinates supplied by the cross line laser are digitally encrypted (hope this word satisfies the computer buffs)
Data could be processed to guide a robotic tool in the manufacture a craft, which for whatever reason is desired, needs to be a copy of the boat being measured.

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## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by Lugalong
Supposedly, besides the wire you don't even need a lines drawing, if the co ordinates supplied by the cross line laser are digitally encrypted (hope this word satisfies the computer buffs)
Data could be processed to guide a robotic tool in the manufacture a craft, which for whatever reason is desired, needs to be a copy of the boat being measured.
Its certainly the case that you can generate the gcode for cutting a replica of the hull from a series of cross sections,a centreline profile and a sheerline.Not enough to generate construction information,or internal layout details.Also not difficult to generate a surface model of the hull for rudimentary hydrostatics.I suspect a scanning laser could generate a hull surface mesh in about three minutes,should one be available.I wouldn't decry any of the systems,since they all work but you should probably keep them all in mind for the future and select what works best for the particular project.

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## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by John Meachen
Its certainly the case that you can generate the gcode for cutting a replica of the hull from a series of cross sections,a centreline profile and a sheerline.Not enough to generate construction information,or internal layout details.Also not difficult to generate a surface model of the hull for rudimentary hydrostatics.I suspect a scanning laser could generate a hull surface mesh in about three minutes,should one be available.I wouldn't decry any of the systems,since they all work but you should probably keep them all in mind for the future and select what works best for the particular project.
The wire datum is certainly worth keeping in mind.....having previously been in a situation where hugely expensive advanced technology had to be ignored in favour of 'primitive' plumb bob and tape measure method of surface mesh creation.
being able to deal with the practicalities of this 3d reverse lofting process (without the aid of anything like a scanner), certainly helped in the contstruction and also with internal layout details.

16. ## Re: How to take Take Hull Lines off an existing boat?

Use caution with a "construction grade" laser level. The accuracy can be all over the place...
A "normal" range of a "good one" may be 1/8" in 30 ft, which is - ah, not really very accurate. Not to mention the size and shape of that dot against an oblique surface can be "interesting".
You need to prove your laser.

(We have self leveling lasers at work that can be set to about 1/16" per 100ft' and they have an accuracy selection so you don't go crazy. But these still should be proven before critical work and they are pricey)

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## Re: How to take Take Hull Lines off an existing boat?

We went into this in depth about a year and a half ago.
Jay

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## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by Peerie Maa
Can you post pictures? I would be interested and I expect MMMike would be as well.
Nick, I will work on this. My Shop/Business website is still under construction, but it looks like we can now post pics from our own computer. Ive been lazy, and tied up with boat projects.
I would like to find out the purpose of these tools...

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## Re: How to take Take Hull Lines off an existing boat?

The scanners I referred to in my previous post shouldn't be confused with laser levels-take a look at http://psg.leica-geosystems.us/page/...aser-scanners/ .I can't visualise the day when every independent boatbuilder will have one on hand,but I can easily see that hiring a man with a scanner could be done in a similar way to sending cut files to a business with a CNC router and then dealing with the output when it is delivered.A while back I saw a Nova documentary where they scanned the interior of a mediaeval cathedral to identify the amount of movement that had occurred and it was a very swift process.Nearer to home I know a company that uses similar technology to record the shape of historic racing cars so that should they get bent a bit there is a record of the shape they should be returned to.

20. ## Re: How to take Take Hull Lines off an existing boat?

Just an update with some information about laser-scanning or photogrammetry devices for boat hulls. Caveat: I have not personally done any research on this subject for some time; what follows is the comments that I have received from my client, whom has looked into the subject as a business activity, in consultation with an engineering firm very active in the field. My client is expanding a facet of his business in which he provides drafting services to regional boatyards who build commercial vessels in the 30- to 65-ft range. One of the requirements of the service is to be able to produce lines plans of existing hulls with sufficient accuracy to be able to have stability analysis performed from the lines. He has discovered that to purchase the equipment capable of laser-ranging the hull surface or photographing it to applied ranging targets, saving the data to a digital file, and converting the data to a format useable by readily-available 3D modelling software such as Rhino, AutoCAD and others, is very expensive. The lowest-cost system of measuring hardware and conversion software that is available currently was priced at approximately CDN\$17,000.00.

Too rich for my blood - I'll continue to use a tape measure. However, if any readers of this know of a off-the-shelf system capable of doing all the required tasks at a lesser price, both my client and myself would be interested in hearing about it.

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## Re: How to take Take Hull Lines off an existing boat?

Check intoa Faro Arm or similar CMM. Run a track along the length of the hull, mount the arm on it, and measure offsets at suitable stations along the length. Most companies want all your info before they will quote prices. The articulated arms may cost less than laser scanners, but they will be slower to use.

22. ## Re: How to take Take Hull Lines off an existing boat?

A couple of years ago I was asked to create a stability book and docking plan for an existing 125' fiberglass motoryacht. No lines drawing was available and the hull was just too big for me to measure by myself with a plumb-bob and tape (my usual method). The boat was inside a shed, sitting on a cradle, with no reasonable clearance at all. So we hired a land surveyor with a transit and helper to come in and shoot some station data. It may have taken them three days due to multiple moves, I spent another couple of days with a tape getting the ends sorted out. Now I'm fitting surfaces to that data. The section data looked like this.....

NDsections2.jpg

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## Re: How to take Take Hull Lines off an existing boat?

Have you fellows come across these devices? https://www.prodim-systems.com/ Much less costly than a Faro arm or laser scanner and you can leapfrog along a large object.You will have to create a surface through the point cloud and then offset by the radius of the tip probe.Still a hefty outlay (probably around \$8000),but If you are doing the job professionally you need to be able to do the job in a competitive time or the fellow who did buy the equipment will have less competition and will prevail.

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## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by Peerie Maa
Can you post pictures? I would be interested and I expect MMMike would be as well.
Nick, I just posted pictures in a new Thread, "Lofting Tool Mystery" in the Tools section

25. ## Re: How to take Take Hull Lines off an existing boat?

Just skimmed the thread, so sorry if this has been covered:

As I was taught, the centerline thread needs not to be straight in the horizontal plane (it probably won't be anyways even without any sagging since the stems are of different heights); the idea is to get a vertically straight line. Then you put a straight-edge across the boat at 90 degrees to the line and you have a vertically and horizontaly correct cross-hair. *
Of course, due to deformations of the hull and other aspects it may need to be tweeked.

Questions:
How do you measure the thicknesses of the strakes on a carvel-build?
How do you measure the width of the landings (the overlap) on a clinker-build? (If not obvious due to the method used at the stems or otherwhere.)

* Edit: With adjustments made for example with the help of a flat surface that the boat is sitting on.

/Mats

26. ## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by mohsart

Questions:
How do you measure the thicknesses of the strakes on a carvel-build?
How do you measure the width of the landings (the overlap) on a clinker-build? (If not obvious due to the method used at the stems or otherwhere.)

/Mats
Transoms are really useful if you need to find the plank thickness. If you have clear access at the maximum section you could measure the beam inside and outside and halve the difference.
If you think that the laps are non standard, you could measure down from the seam nails outside and up on the inside, add the results and average over several measurements. Be aware though, if like my Shetland ella boat she was not built over moulds that the lap widths can vary over the entire hull.

27. ## Re: How to take Take Hull Lines off an existing boat?

Good points, I didn't think of that the rivets tells the story even if not placed in the middle of the lap or goes a bit imperfect through the lap. Same with transoms, too bad there are double-enders as well.
What is a standard lap? I believe 2 cm was pretty much standard here in the 20th c, probably an inch before that (what inch I don't know, but probably not the Swedish inch that was almost 3 cm and not used for long). And larger laps was probably used for larger boats...
Nail-heads and even roves may be hard to spot on boats where you don't want to remove paint/putty/black varnish etc, but that is perhaps out of scope here.

/Mats

28. ## Re: How to take Take Hull Lines off an existing boat?

Originally Posted by mohsart
Good points, I didn't think of that the rivets tells the story even if not placed in the middle of the lap or goes a bit imperfect through the lap. Same with transoms, too bad there are double-enders as well.
What is a standard lap? I believe 2 cm was pretty much standard here in the 20th c, probably an inch before that (what inch I don't know, but probably not the Swedish inch that was almost 3 cm and not used for long). And larger laps was probably used for larger boats...
Nail-heads and even roves may be hard to spot on boats where you don't want to remove paint/putty/black varnish etc, but that is perhaps out of scope here.

/Mats
According to Eric McKee''s research the lap is normally twice the plank thickness.

29. ## Re: How to take Take Hull Lines off an existing boat?

Just to wrap up my involvement here: In post #42 I said I was going to measure a boat using the two-wire triangulation method. Well, I went out to the boatshop to measure the boat yesterday and was unable to do the job. The measurement method requires at least two metres (six feet) of free space on one side of the hull to set up the datum wires and measure the hull. Lobster boats are getting so wide around here that they are completely filling the shops they are built in. In yesterday's case, the boat came to within a half-metre of the shop exterior wall, and within ten centimetres of the mezzanine deck on the other side, making it impossible to measure the hull by triangulation. There is six centimetres (2-3/8 in.) clearance on each side of the boat to the door frame it has to be pulled out through. This is a fifty-foot, fifty-eight tonne boat. I am glad that I am not the one charged with getting the boat out unscathed.

However, there is a silver lining in this. The difficulties encountered in measuring this boat has convinced my client that he will go ahead and invest in a laser-scanning hull measuring system and provide measurement services to regional commercial boatyards whom need to provide as-built lines plans to their customers. The boat owners need to provide the governmental regulatory agency with a formal stability analysis of their new fishing boats, so my client has suggested that we look into a collaborative business arrangement where he will measure the hulls and produce a 3D model of the hull, and turn the dataset over to my company to produce the required stability booklet. So the trip to the boatyard was not wasted. Win-win.

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