Drawing programs

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OldCreek
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Drawing programs

Post by OldCreek »

What are you guys using to draw up your boat ideas?

For example, Bill drew mock up pictures of how Bolero (Shields conversion) would look with certain design aspects as well as cabin and rigging layout. I've seen plenty of others. Also, do these programs allow for technical information? i.e. determining length, etc.

I downloaded a free CAD program online: Draftsight, (3ds.com), but haven't invested any time into it yet. Thoughts?

Ultimately, the idea is to mock up a daysailer project like Glissando or Bolero.

Thanks,

Wil
Zach
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Re: Drawing programs

Post by Zach »

Are you wanting to pull line plans off the drawing, or are you working around an existing boat?

I use an ancient copy of Bob Cad from the DOS age for 2d drawings... and Solid Works for 3D/solid models.

For the outside lines I use a pencil. Pictures that are blown up to an accurate scale. Measure the boat, measure the picture and use a drafting scale. From there I use tracing paper to trace the cabin and sheer. Drafting dots hold the original printed image to a shadow box (or a glass coffee table with a drop light under it...)

Once you have the lines you want to see, your scale still works to pull the proportions. Then if you have a line drawing, or are making a line drawing you index your heights and locations on your sketch to match up.

With that in hand, you have your offsets for the cabin and its location and height in space.

To go to much farther than that, gets on the verge of wasting time if you are working off an existing plan or design. It will be, what it will be once you are standing in it, and the space that is shown on the computer is not there when you are standing in it. You can make a very accurate and beautiful computer model of the boat, but if it is an existing boat I strongly encourage taking the minimum of measurements that will get the LWL, Buttock lines, stations, and frame spacings imported in. The buttock lines that count for interior space are the floor, 25in, 36in, 5ft, and the sheer. Basically everything beyond that begins to overdefine the shape and you will be frustrated that it won't skin in to a model.

Don't lose yourself making a model that is perfect, because boats are not perfect. Believing you will be able to pull the offsets and build parts off the model, only works on boats built on CNC routed jigs, and even then you will still add 2 inches to the hull side, and need every bit of it for a scribe. Old plastic boats were built on wooden plugs, and the Transom on Pylasteki is off 3/4's of an inch from the Center to the port side... And the aft end of her cabin is not perpendicular to the centerline by an equal amount. Lay one bulkhead on the other before you glass them in and they are very very different in height, shape and curve, for an existing boat.

Custom ones can be perfect, there are a few shops around here that strive for that level... but on the backyard level the same labor and effort means a few more years boat building and less sailing.

Blue dow foam boards make the best models, as you can cut them with a knife and use long sheet rock screws to hold them together.

Off the soap box...

To get the hull into the computer, a line drawing helps immensely. A table of offsets helps. I forget exactly what the excel formula looked like to go from Feet, Inches and 1/8ths to decimals but it is doable with a table...

The easy way is to import the line drawing as an image, and scale the image to be the actual size of the boat. 1:1.

Then with a series of layers, use the snap function to create a spline of each station mark. The layer tool lets you number each...

With that done, you move each layer to the station it is supposed to be. Mirror it to the other side of a plumb line marking the center of the keel. Most line drawings don't give a clear indication of what the width is supposed to be at the keel/bilge area this is one of those things that gets solved during lofting with battens. Computers don't make nearly as good a batten as a piece of fir...

Anyway, after you have the stations marked you'll spline a curve that follows the water lines, the spacing is shown on the drawings. .. Others have different spacing at different heights.

This requires a bit of noodling, as measuring down the length of your line from the sheer down doesn't solve it... You have to measure from the center plumb line down 6 inches, a foot, what have you to where it intersects the curve. Then you pop the line around it.

Some programs have a skin function but without defining the bow more than what is in real life and your stem won't go together straight. Your horn timbers... err... The sides of your transom won't mesh out as the battens of the real world extended out past those points. At the least, the bow and stern quarters need a bit of extra loving and tweaking to get where the lines look right. Also to get the bevel on the transom you need a bevel board for the real boat... Bevel gauge with a level, and a board that reads out the angle in degrees. If you have the line drawing, you'll work the protractor a bit to get an accurate read.

To blow up a line drawing, a pencil line on a piece of paper small enough to carry blown up to full scale is fatter than 3/16th. If you have two sides of each line, there is a significant fudge factor involved to get the lines to flow out and work together. If the guy drawing the line was off a bit things go haywire fast... So take creative liberty and do what needs to be done to get the port and starboard to line up. The easiest way is to bump a layer in or out at the keel and sheer line a fuzz....

Now that you have an empty cup on the screen, your line drawing should lack the deck drawing. You can either run a camber that changes its radius at each station mark, or have one with hills and valleys. Study the boat and see whats happening on board. Most boats have a combination where the bow goes flat, or the center is pumped up a bit more than the rest so they have a flatter line when viewed from the side.

Boats aren't symmetrical on deck either I'm working on one that has studs that are absolutely perfectly level, but the house is an inch and a quarter off to one side of the centerline. When you draw two points, the front and back of a cabin... swing an arc and account that somewhere along that arc and the intersection with the lubbers line is where it'll go. Often the side deck distance doesn't pan out the same, make a sanding block for one side and its to long for the other.

Also, you may lose 4-6 inches if the sheer line on a drawing is not the deck joint, or is the rub rail but not the top of the deck. This depends largely on the guy who penned the line originally...

If you have the boat but no line drawing, you can pop the lines off her from the inside if she is gutted (It is harder but not impossible from the outside. Pop a string parallel to her and to the same thing of measuring over. Depending on the accuracy you are after, this can be easy or a bit more complex. I haven't done it that way...

From the inside:

Level the boat. Get a straight line running from the center of the stem to her stern. If it is level that will help. From the inside you need a straight line to be center. I like a laser on boats shorter than 40 feet to define where the string needs to go, as a line level sags the line. Your string needs to be at least 17lb stuff, I like carpenters twine. I wrap it around a wooden block with a V in the block to catch the line and screw it down. If you have to glue/5200 a block to the stem and transom to have something to screw to... go for it. Leave the line 6-8 inches short and stretch it, get the screws started and sink it home.

If you use a laser you need a tripod of sorts, to pick up the straight line. Laying the laser on one side or the other doesn't work, as the surface you are laying against would have to be perfectly square to the centerline of the boat. An 1/8th inch out or a pucker in the surface is a big time error at the other end.

From here, you'll drop a plumb bob from the top of the cabin, kissing the Center line. C with a line straight through it on your note book.

The plumb bob will hang down, and you'll put a mark every foot, or so... It depends how the boat wants to be measured. If you have bulkheads on the foot exactly, then fudge it so your stations are close but not hitting the fillets and stuff that can't be measured.

From here it takes two people, with a folding extension rule(!) measure from the plumb line out on 6 inch heights to the outside of the hull. This develops your spline, that becomes the outer curve of the hull. You can do both sides, but the actual boat is probably not within the accuracy of your CAD program to solve on its own.

You are also measuring the internal dimensions, not the external ones... so you have some fudge factor in the laminate schedule/hull skin thickness that makes the inaccuracy of port and starboard not a big fish. On bigger boats its fairly standard to take a full width measure, with three tape measures... One to get the width, and two to get the same height off the floor, then dividing by two to get the C-line.

It is a lot easier to skin it, and then add thickness to a 3D model than it is to bump over a spline in space what the average thickness might be.

If you have the labor a 2x3 aluminum box tube is handy with a level strapped to it and a few extra hands to get a periodic width measure and having someone taking down the measures goes quickly. Level on each side down to the outside of the hull or plumb bobs hanging down past the hull and a scale written on the box tube is fairly straight forward. On small stuff dropping a plumb bob to the floor and moving the boat is equally easy. Where you have blocking for the keel is a bit harder on the big stuff, or if you aren't on a hard floor.

Zach
1961 Pearson Triton
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carterskemp
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Re: Drawing programs

Post by carterskemp »

I use Rhino 3D. On both OS X and on WIndows. The Mac version is officially beta, but has become quite robust over the last couple of years. I like it for it's ability to quickly mockup 3D shapes as well as it's similarity to AutoCAD when working in 2D. It's not cheap at $1000, but if you are a student or teacher they have a great deal at $195 for a full version.

Although it was designed as a full-on marine 3D application, for my boat stuff I use it mainly in 2D for simple layouts and material calculations. Google Sketchup could probably stand in fine and is free. As with any new to you computer software, plan on a learning curve. Work through a couple of tutorials and you will probably get good enough to do the simple stuff that helps when working on a boat.

Good luck.

Carter
Tallystick
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Re: Drawing programs

Post by Tallystick »

Blender is free and there are some add-ons with additional CAD features.
Quetzalsailor
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Re: Drawing programs

Post by Quetzalsailor »

AutoCAD is terrible for this purpose and, of course, far from free. It does not handle surfaces or volumes the way a proper naval architecture program would. It's obviously 'smart' enough but that's not what 'saddle programs' have been developed for it to work through. For example, there are saddle programs for piping engineers, architects, etc.

It is, however, the 'industry standard' for all sorts of technical purposes. I'm an architect so this is the program I use. I've sent drawings of boat parts to fabricators and they work to 'em. I've worked through interior modifications with the program. I've made full-size patterns for parts with the program. I'll post an example later.
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OldCreek
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Re: Drawing programs

Post by OldCreek »

Thanks everybody for your input.

Ironically, I was thinking that my venture may need to start with graph paper...

Wil
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Re: Drawing programs

Post by Surveyor »

Like Quetzal, I use Autocad but a version for surveying and mapping. Have any old charts and NTMs that you wish to have superimposed on them? :P

CAD is great for some stuff but terribad for others concerning boats. Graph paper, tick sticks and your minds eye are really the best tools you can ask for. With that said, I totally geeked out with cad when I bought my project boat. Here is an example:

Image

In this file I have:
° Imported, rotated, scaled and aligned 3 drawings. They are 1:1 (measure correctly within reason)
° Drew a D5 dinghy from plans and placed it on the boat. (in plan view to see what room was left to pass to bow)
° Drew an AirHead composting head in the bow to check fit. (checked before ordering!)
° Extended the apparent rudder shaft up and aft to the aft deck for possible tiller placement out of the cockpit. (hits laz, no go)
° Played with a radar tower design to miss backstay. (little boat, 200# tower...no)
° Messed around with saloon/galley layout (same can be done on a print)

A work in progess is this mock up of a flush mount gauge box, made from 1/4" G10, to go in/on the aft face, port side of the cabin above the footwell of the cockpit:

Image

Now I am just showing off!

Your graph paper is just as good as any of the above. Probably better because it will be based upon careful, prudent measurements made by you.
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