Digitizing a Boat Hull: Mac26 Modeling Data

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In summary, Tom has been trying to figure out a way to data model his boat's shape, but he's not sure if the data needs to be accurate or if it just needs to look smooth. He's also Unsure which way to go about it. One option is to take low-resolution data and use it as guidelines to build the model manually, but that would mean the chines would be perfectly straight. Another option is to take measurements every few feet and join the data points, but this would be more work. He's also considering a digital tape measure, which would have accuracy of 3mm.
  • #1
DaveC426913
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TL;DR Summary
Want to digitize my boat so I can print it out. Looking for a low-tech solution for the digitization process.
My boat (Mac26) is not revered enough for anyone to have bothered to data model its shape. My Mac26 friends have all expressed an interest in getting their hands on it.

I've been trying to think of an expedient and cost effective way of modeling it in data form.
One way is to place equally-spaced markers on it every few feet and then photograph it from the front-back, and that should give me cross-sections.
Another way is to make some sort of L-shaped wood frame, calibrate it with the centreline, and move it along the hull, writing down X,Y measurements as I go.

I'm not sure the data model needs to be all that accurate to the real thing, but it's got to look smooth. (So, precision is more important than accuracy**.) Maybe a slice every foot along its length - tighter near the bow. Widthwise is a little trickier, since the hull does have chines and rub rails and stuff, meaning I might want a much finer resolution.

Also I'm not sure which way to go:
  1. Get data that's high enough resolution to use it directly for the 3D modeling (in Blender) by joining the data points. This would be more work at the boat, but less in Blender. The downside is that it would be a - er - "voxelated" model (3D equivalent of pixelated). The grid of data points would not align with the vertices of the hull.
  2. Just take low-rez data and use it as guidelines to build the model manually (in Blender). This would mean such things as the chines would be perfectly straight, since I'd be drawing them myself, effectively as straight line vectors.

**
Screenshot%202019-06-21%20at%204.03.26%20PM.png

(I'm super pleased that I am able to employ this infographic in an actual explanatory role!)Confounding factors:
- Can only practically take measurements while it's "on-the-hard". Otherwise the paper gets soggy and I have to stop every two minutes to breathe.
- Very awkward to get at some parts of hull because of the trailer.
 
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  • #3
I seem to recall that several years ago, Microsoft made a 3D camera from which you could determine distance to an object in the image. I also seem to recall that they soon quit making/selling them. :cry:

A current approach I can think of is a Digital Tape Measure. They are handheld, battery operated, and have a read-out. Some operate by timing the round trip travel time of an ultrasonic pulse, and may have a Laser beam for aiming. Others seem(?) to use the travel time of a laser pulse.

https://www.google.com/search?q=digital+tape+measure+with+laser

This one seems to use a Laser - and claims 3mm accuracy, the manual is at:
https://www.bosch-professional.com/tz/en/products/glm-20-0601072EG0

Maybe you can find one with data logging or digital output; if not, have an assistant write the results or photograph them with a cell phone for later data entry.

Have Fun!
Tom

p.s. You might even be able to make a profit from the data.
 
  • #4
DaveC426913 said:
Widthwise is a little trickier, since the hull does have chines and rub rails and stuff, meaning I might want a much finer resolution.
The chines are probably the key features. The area between chines is usually filled with a flat sheet, curved and twisted to follow the chines. The chines are usually fixed height steps, made by overlapping sheet material during construction. That all makes it easier to fabricate a plywood or steel hull, or a fibreglass mould, from sheet material.

Which version: 26D, 26S, 26X or 26M ?
 
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  • #5
Plenty of photogrammetry programs. Fine tuning the process is rather time consuming, but there are tons of tools and tutorials, many of them free,
 
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  • #6
DaveE said:
Seems like a SW purchasing problem. I know you can create 3D models from multiple 2D images.
Borek said:
Plenty of photogrammetry programs. Fine tuning the process is rather time consuming, but there are tons of tools and tutorials, many of them free,
My question is really meant to be more about gathering the raw data.
 
  • #7
Baluncore said:
Which version: 26D, 26S, 26X or 26M ?
X! :)
 
  • #8
Tom.G said:
A current approach I can think of is a Digital Tape Measure.
Hadn't thought of that. It solves part of the problem , but id still need to make a whole scaffold to act as a calibrating grid for measurements.

I wonder how accurate it can be at the highly oblique angles this will require...
 
  • #10
Maybe take something like a laser level turned on it's side, that would paint a vertical line on the side of the boat, then take a series of pictures as you moved the line down the length of the boat. You would probably need a fairly long lens to avoid perspective distortion.
 
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  • #11
sandy stone said:
something like a laser level
Huh. I have one of those...
 
  • #12
Here's how I would attack the problem.

Start with an accurate grid marked on the floor. Mark a series of points on the boat with masking tape. Use a plumb bob to mark the corresponding points on the floor. Measure vertical distance with a laser measuring tool. My laser gadget reads to 1/32", and appears to be repeatable within 1/32".

Get a copy of Lofting by Allan H. Vaitses (https://www.amazon.com/dp/0937822558/?tag=pfamazon01-20). Dive in and have fun.

Yes, I have a copy of that book. I bought it when I had ideas that were larger than my willingness to execute them. Turned out that I would rather read about boats than build another one.
 
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  • #13
jrmichler said:
Use a plumb bob to mark the corresponding points on the floor. Measure vertical distance with a laser measuring tool.
Your floor-based grid sounds like a good idea.

Though the laser measure seems redundant. I'd have to ensure the tool is plumb to get proper readings. I might as well just put marks on the plumb line.
 
  • #14
Wish I could raise it off the trailer!

Back in the day I had 5000 pound straps and a chain winch, and a friend with a barn that had been used as an engine repair shop so it had a huge steel beam in the rafters.

Painted the hull of my first boat that way.

Good times, good times.
 
  • #15
DaveC426913 said:
My question is really meant to be more about gathering the raw data.

I could be wrong, but the photogrammetry setups I've seen use what is essentially regular cameras. For high-precision measurements you presumably need some good lenses etc (to avoid artefacts), but for what you want to do I would have thought a regular mobile phone camera would work.
 
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  • #16
f95toli said:
I could be wrong, but the photogrammetry setups I've seen use what is essentially regular cameras. For high-precision measurements you presumably need some good lenses etc (to avoid artefacts), but for what you want to do I would have thought a regular mobile phone camera would work.
Oh!
 
  • #17
DaveC426913 said:
Huh. I have one of those...
I once built a real time stereometric locating system for an array of medical transducers. The design used little "scotch light" retroreflectors on each sensor and two cameras. The video image from each camera was a field of bright "tiny planets" and my software could locate these in 3D to within a millimeter. One of my better efforts!
So such software must exist and I know that the retroreflectors are used for kinesthesiology for athletes. Might be a good approach.
 
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  • #18
DaveC426913 said:
My question is really meant to be more about gathering the raw data.
Which most serious tutorials cover.
 
  • #19
Borek said:
Which most serious tutorials cover.
Yes. My mistake. I thought photogrammetry was a software thing, not a data collection thing.
 
  • #20
I sell metrology level scanners to scan surfaces to 0.0006" accuracy.
There are many hand held optical scanners on the market today. Most have accuracy to 0.002 to 0.003" and can convert the scan to 3D Cad model. You may have to put stick on dots on the hull so the scan sections can be stitched togeather. The attached is available at about $ 5000 US. many source
I do not sell cheap lower end scan stuff. Einscan is whole package.
Just saw einstar on amazon for $ 950..worth checking out

https://www.einscan.com/

https://www.einstar.com/
 
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  • #22
berkeman said:
What is being scanned here?
The friends we made along the way.
 
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  • #23
one ugly shirt...some where a 59 Pontiac is missing seat covers
 
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  • #24
Wish I could raise it off the trailer!

Reference: https://www.physicsforums.com/threads/digitizing-a-boat-hull.1049642/#post-6851855

You can, if you really want to (with a hydraulic jack, some blocks and a bit of lumber). The trick is: Jack/Block the entire assembly (trailer, boat) to the desired height, support he boat with properly shaped/located bunks, and lower the trailer. I periodically re-paint the bottom of my Catalina 22 this way. I use 10'L doubled 2x10's with wedges as bunks and 4x4's as standards.
 
  • #25
DaveC426913 said:
One way is to place equally-spaced markers on it every few feet and then photograph it from the front-back, and that should give me cross-sections.
As I'm sure you know, those markers will be required for any photography based method. In particular, measurements will be made on the edges and corners that show up in the photos. An alternative to discrete markers would be to use a water colors to paint a checker-board pattern onto the surfaces.

Depending on the software used to process the photos, long straight edges have a potential for more precision. Similarly, 90-degree corners have the potential for greater measurement precision.
 
  • #26
Here is a crazy idea. How clear is the water ? Can you wait until summer and shoot underwater images?. Obviously you would also need above- water ones for the topsides. You could put water ballast in the bilges to assure (a well marked) overlap area allowing "stitching" the topside and underwater renderings together at scale
 
  • #27
hutchphd said:
Here is a crazy idea. How clear is the water ? Can you wait until summer and shoot underwater images?. Obviously you would also need above- water ones for the topsides. You could put water ballast in the bilges to assure (a well marked) overlap area allowing "stitching" the topside and underwater renderings together at scale
But what good would underwater pictures do? It doesn't help with coordinates.
 
  • #28
DaveC426913 said:
But what good would underwater pictures do? It doesn't help with coordinates.
With clear enough water, a good underwater camera set-up and a bars grid painted onto the hull (with removable but water-resistant paint), it could be done. You would need software to convert the images to coordinates.
I'm not sure if free workable photogrametry software has been identified in this thread, but here is a list:
all3dp.com photogrammetry listware/
I may try one later this weekend.
 
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  • #29
Currently, I am leaning toward jrmichlers suggestion of a grid on the ground and a plumb bob.

Doesn't help with topsides tho.
 
  • #30
How many data points do you want to collect?
It sounds like a 2-person job. One with the plumb bob, the second recording the results.
 
  • #31
.Scott said:
How many data points do you want to collect?
As few as needed.

This is not for widespread consumption. It doesn't need to be centimeter accurate.

Basically, the IRL equivalent of a low poly mesh. Maybe 100 data points, strategically chosen. Basically, until I get sick of lying on the gravel parking lot under my trailer.

I can interpolate from 100 and add curves. And of course only one half of the hull needs doing.

Topsides will actually be the bigger challenge. Much more detail
 
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  • #32
How about a big contour gauge thingy used in conjunction with a laser level line and maybe a bubble level on the gauge. I remember seeing a 50 cm long one once. Still damned tedious though.
 
  • #33
I recommend Meshroom because I like the name.
 
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  • #34
There are Mac26X hull photos here.
https://www.boatsonline.com.au/boats-for-sale/used/trailer-boats/macgregor-26x/281571
The hull lines appear to have been developed from flat sheets, so only the several chines, keel, and gunwale on one side need be measured. The surface is simply ruled straight between each pair of adjacent lines.

Park your boat next to a brick wall. Mark points about one or two feet apart, along the lines where the sheets were joined. Note the step profile at the joints. Measure the position of those points from the wall and from the ground. That gives the hull lines.
 

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