Reading Boat Drawings

[Julie Mo]

I think I'm beginning to understand boat drawings.  I have seen line drawings many times but never stopped to figure out what is going on.  It wasn't until I began my first model that I actually started to put it all together.  But I'm not sure I have this right.

What I think I am seeing with the hull lines is the frames from the bow to midships on the right and from midships to stern on the left.  So if you cut the drawing above down the middle, and took each half and made mirror images of the other half, you would have all the frames necessary to duplicate the shape of the hull.

 

Next you take those frames and place them where the vertical lines are on the above drawing, from "0" to "20".  Then you plank it and you have the hull.

 

Am I on the right track?

[thibaultron]

Yes

[Julie Mo]

Thank you, Ron.

 

Next question, when looking at the bottom picture in the first post, the lines from bow to stern should be created by the planking.  Right?

 

Same with this drawing...  I can see it adds the water line and the keel and rudder shape.  But as far as the hull shape, that should be created by the frames being placed in the correct location and planking the hull?

[mtaylor]

Julie,

 

Have a look here.. http://modelshipworldforum.com/ship-model-plans-and-research.php

 

The second article by Russell Barnes.  He pretty much explains everything on the drawings.

[trippwj]

Julie - you are off to a good start, but a couple of corrections.

 

The first body plan - the lines are station lines which, in most cases align with a frame but not all frames are shown. The curved horizontal lines in your next query are somewhat arbitrary lines. They are waterlines decided by the draftsman representing fixed intervals up from the baseline (they are straight horizontal lines in the sheer plan). They show the shape of the hull at that level.

 

The curved lines in the final plan do not show planking, but rather hull shape at a fixed distance out from the centerline (imagine slices from bow to stern). Again, the size of each slice was somewhat arbitrary, though fixed on a given plan.

 

Confused yet?

[Julie Mo]

Thanks for the answers, guys, but please don't dismiss the class yet.

 

I understood everything you said, Wayne.  I figured the lines on the top view and side view drawings were planes slicing through the hull.  What I didn't figure was the station lines may not necessarily reflect frame shape and location.  I thought they were there specifically to design the frames.  But I would imagine if you made frames based on station lines, you should replicate the intended hull design.  Correct?

 

For model building purposes, could you use the station lines to create the frames?  And, theoretically, should that method give you a reasonable facsimile of the actual ship/boat hull?

 

 

[Julie Mo]

Julie,

 

Have a look here.. http://modelshipworldforum.com/ship-model-plans-and-research.php

 

The second article by Russell Barnes.  He pretty much explains everything on the drawings.

Mark, thanks for the link.  I had been on that page but missed that particular article.  I read through it and I think I pretty much understand what's going on. 

 

Next step for me will be to apply my understanding of all this into a CAD drawing.  I have AutoCAD MEP, which is intended for mechanical, electrical and plumbing in buildings but I can make it work for modeling purposes.  It will be interesting to see how this works out. German Frers, look out!     

[Julie Mo]

Let's see if I am on the right track...

 

I took a line drawing of Endeavour II and drew over the body, breath and sheer level lines (do I have those terms correct?)

 

Then I put it into 3D and rotated the lines to get them into the correct x,y,z planes

 

So if I draw in all the buttock lines and orient them properly, I should have a 3D line drawing. 

 

If I take those same buttock lines and create planes with them and loft them, I should be able to create a 3D hull.

 

If I'm missing something, please let me know.

 

Thanks,

Julie

[lehmann]

I'm assuming here that your underlying question is how to use the lines drawing to build your model....

 

Each set of curves, sections, waterlines, buttock lines, (and even diagonals) could be used individually to describe a hull.  Layers of wood, of the appropriate thickness and profile, can be glued together and smoothed to form a hull.  This is basically, old-school 3D printing, where the thinner the sections, the less smoothing is needed.   You can do this in any of the three directions (if you're really good, you could even glue up wedges shaped from the diagonals!).  One professional modeler, Phillip Reed, makes his frames by stacking layers longitudinally with each layer having the thickness of the frame.  He then smooths the solid hull.  When done, he removes every second layer to get a set of evenly spaced frames ready to be attached to the keel.  

 

The other method is to build sections, which are basically the same as the frames used in construction of a full sized wooden hull if the thickness of the planking is accounted for.  As mentioned in a previous post, the location and spacing of the sections in a lines drawing are arbitrary and chosen for the convenience of the the designer, mainly to make the calculations for displacement and stability easier.  In construction, there are many more frames than there are sections.  Even for a plank-on-bulkhead model, it's a good idea to have more bulkheads than there are sections in the plans so that the planking is better supported.  To get the frame or bulkhead shapes, just add new section lines to the drawing where ever the frames are to go.  In some ships some of the frames are not square to the centerline (in the plan view), but are canted: you can work out the shape of these canted frames by just adding canted section lines and working out their shape. There are also drafting methods to get the shape of the transom.

 

So, yes, you can get a 3D shape of the hull from the drawings, but you may not want to use it directly to build your model (or real ship). However, you can extract all the shapes from the lines drawing.  

 

A few points to consider:

• Since the frames have thickness and the surfaces will have to be beveled so the planks fit properly, the profile of the sawn frame has to be from the widest side of the frame (usually, the side closest to mid-ship)
• As mentioned above, take into account the thickness of the planking when drawing the frames.  In plank-on-bulkhead construction it is common to use two layers of planking (double-plank) to better ensure that the final planking layer is properly supported and fair (smooth).

For a full ship ship, these details are worked out by on a full size drawing - and the process is termed "lofting".  

 

Bruce

[mtaylor]

Julie,

 

As I recall, that link to the database, there's a multipart tutorial on using AutoCAD for this.  I'm not sure what "level" it is for, however.   By level.. newbie, mid-level that has some knowledge of AutoCAD and ship's lines, or expert.

[captainbob]

Basically what you said and what you have drawn is true.  If you add all the section drawings at the correct place you will have a 3D drawing of the boat hull.  Once you get skin on the hull you can cut across it at any location and get a new section.  If the frames on the boat are at every 9 inches then a cut at every 9 inches will give you all the frame shapes.

 

I build POB and usually use only every third or fourth section lines that are drawn for my bulkheads.  That is plenty to support the planking.  Just remember as you are drawing, the lines are usually to the outside of the hull, so you need to remove the thickness of the wood you plan to plank with.

 

Bob

[JohnE]

Hi Julie.

 

I'm doing much the same thing on a different model. I'm going towards wood and not 3-D, but same, same.

 

Can help. Shoot me a pm. I routinely use Corel and TurboCAD, but AutoCAD is a no-brainer.

 

John

Edited December 14, 2015 by JohnE

[Julie Mo]

Thank you for the replies.  I absorbing everything like a sponge.

 

I started taking the body lines and making full frames.

 

After rotating them into their 3D position, I placed the front frame lines in their respective locations.

Working from the inside toward the outside, I placed the frame lines at each point along the hull.  I made an operator error that isn't so evident in this picture but I was able to fix it without a lot of trouble.

 

Next I placed the back half of the frame lines in position and moved them from stern to midships working inside to out.

As you can see, the back half didn't come out as well, relative to the keel line.  If I moved the frames so they better line up with the keel line, the width of each frame line doesn't fair properly from one frame to the next and on from there.  As it is in the picture above, they do.  Since I was unable to decipher the frame numbers on the PDF, I just placed them according to their position on the body line drawing.

 

I was pretty exact when creating the body lines but the lines were a blur when zooming in close.  And at the keel section, it was hard to tell if any of the lines crossed over one another.  Some just melted into each other.

 

This is just an exercise to help me understand boat design and see how I fare.  It's keeping me busy as we approach moving day.  I doubt I'll ever use this for a scratch build but it's nice to use it as a learning experience.  

[captainbob]

I find it rare to find accurate lines drawings.  (If you have offsets they are usually better.)   That's why I redraw them and make the necessary corrections.

 

Bob

[Julie Mo]

Bob, when redrawing, do you go with what looks good?  Or do you follow something more precise?

 

I'm going to draw over the buttock lines next and insert them in place.  I realize I won't have anything that replicates the sheer at the rail but maybe the level lines will provide some guidance.  Whatever the case, I am enjoying this.  I've been drawing boats since I was in grade school but I never had a clue how to do anything close to design.

[Julie Mo]

I finished the half-breadth lines, mirrored them and put them in place.  Working in a wireframe like this gets more difficult as you add to it.  You have to be very careful you are snapping to the proper place.  Yes, I goofed some of it up.

 

This is an image looking up from the bottom:

 

On the left is the composite of everything I have added to the 3D wireframe.  Middle and right are the body lines I used to make the frames.

I still have to rework the keel area if I want this done right.  I also noticed the half-breadth lines weren't drawn in at every level line.

 

If I am to complete the 3D image, I will need to figure out how to draw a 3D half-breadth outline that will allow for all three x, y and z coordinates.  So far, all I have been able to do is two planes in any kind of line.  AutoCAD won't allow something like a polyline to run through three planes.

[captainbob]

Frequently I find that although the height (draft) of the sections match the height of the profile, the width (beam) of the sections do not match the plan view.  In this case you need to find the proper ratio of LOA to beam to draft.  Then you know which to change.  Sometimes the keel point on some sections do not meat the keel in profile.  I measure from the base line to the keel point on the sections and transfer that dimension to the station lines in the profile.  Draw a line through these lines. If the new line is not fair you know it is wrong and the sections need to be changed.  If both lines are good you need to do more research to determine which is correct. 

 

When a designer starts a new boat, the ratio of LOA to beam is set.  If it is a racing boat, as you are drawing, it will be narrow for the length.  If it is a pleasure boat it may be fat.  The grid lines are laid down.   He then draws the keel and shear in the profile, the deck line in the plan, and the widest section. He makes sure the points on all the lines as the cross the grid lines match.  This is done for every curved line that is drawn. This goes on and on until the plans are finished.  But mainly the designer wants every curved line to be smooth and fair.   The main tool of the drafting board designer is the eraser.

 

All this being said, if you find only one or two lines that do not fit with the rest, change it, by eye, to be a smooth fit with all the rest.  That's my lesson for today.  lol.

 

Bob

[Julie Mo]

Thank you, Bob.  While I won't lie and say I absorbed everything you said, I will say it helps me get a better understanding about how a boat design comes into fruition. 

 

I find myself surprised that something I intended to be a woodworking project to keep me busy during a house hunt (the kit build) has become a door that opened to something I have been interested in for decades. 

[captainbob]

In that case, I'm glad you found us.  There are a lot of good books on boat design.  The one I bought first, many years ago, and still refer to is, "Skeen's Elements of Yacht Design" by Kinney.  Boat design is very challenging, but it is also a lot of fun.

 

Bob

[Julie Mo]

A couple of years ago I bought Understanding Boat Design by Ted Brewer and The Elements of Boat Strength: For Builders, Designers and Owners by Dave Gerr.  The latter was pretty intense and, with the little knowledge I had, was more than I cared to tackle at the time.  Now I'm anxious to find it after the movers arrive. 

 

I worked in the building trades for 35 years and at the end of my career I was taking engineered electrical drawings and redrawing them into construction-ready plans.  That's when I taught myself AutoCAD.  I took to it like a child to Disney World.  Definitely some of my best years in the trades.

 

I saw the Skeen book on Amazon.  They grouped it with two other books as a "Frequently Bought Together" - the two books I mentioned above.  So maybe I'm on the right book learning track.  BTW, I ordered Skeen.

 

Julie

[nancysqueaks]

Julie, rather blown away by these posts, in fact rather in awe...

It is nice to be good at something and still ask questions,

that in my book is great, and really the way to learn.

Good luck, Cheers, Nick

[Julie Mo]

I downloaded the FREE!Ship program and loaded it in today.  I opened a new project and inserted the numbers I had from the Endeavour II drawing.  When the new project opened, here's what I saw:

 

Maybe that 14' draught number wasn't supposed to include the keel. 

Edited December 16, 2015 by Julie Mo

[JohnE]

Maybe that 14' draught number wasn't supposed to include the keel. 

Hi Julie.

 

I think FreeShip looks at body stuff. Keels are appendages.

 

Ciao, John