Lines of a Hull

[kmorin]

Welder, if you think this discussion should be in another location I agree, but since this is an overall topic about boats I figured I'd put it here and let you move if needed?

Lots of us look at boats without 'seeing' as much as we could if we'd spent some time drawing boats, designing boats and to do that the 'traditional' views of the boat plans are important to understand. With 3D and high quality photography, ad campaigns ignore the true hull shape, but that is what makes the boat perform the way it does, or doesn't. This won't make any of us marine designers, but it may help us discuss more accurately what shape our boats are- or should be.

This topic is basically a tutorial for those who are just becoming familiar with hull lines. As with most of these articles I'm trying to explain a topic that is sometimes less discussed because so many experienced builders are already familiar with this topic. Here, we'll take a series of simplified illustrations to accompany the text and hope that anyone reading this is helped as they learn more about hull lines.

The illustrations are not highly curved so the 'curves' will have angle points because the software is set to fewer segments in a curve in order to move more quickly and make smaller files. If you see a hard spot in a curve and it confuses your view of the idea, please don't hesitate to ask and I'll try to clear up what the coarse illustrations may have mis-conveyed.

I'm using a simple dory shape to make these illustrations since the person that I wrote this for was discussing dories with me at the time. Next there are colors used to help separate the shapes and make more clear the distances in these views and all of them are for that purpose alone. Anyone who already designs will have to excuse my license with this information as I'm attempting to give a basic concept and we all know that only those who get out their own pencil & paper will become intimate with this system of geometry.

The lines are a series of projections, or flat drawings of intersecting planes as they pass through a hull. 3D drawing with a computer makes these lines fairly simple to achieve compared to the level of effort needed to draw the same lines flat on paper. These computer illustrations are intended to make images that illustrate the ideas behind the various sets or groups of "Lines" and are not an example of how to draw them with a pencil.

We'll begin with a picture of the three traditional views, Top or Plan View, Side of Profile View, and End or Body Plan view sometimes call the Sections View. If we had a boat with a large sheet of rigid material under the boat, next to the side of the boat and at the end of the boat it might look like this.


here we've rotated our view of this basic three sided box with the boat in the middle



and the last view of this 'open box' is from nearly the Profile View



In the past, before computer graphics and marine software [not to mention illustration software] drawings like this would take quite a while because the technique to make the lines in these different perspective views was time consuming. That meant that a method of drawing that was faster and just as informative had to be used, one that described the boat accurately and allowed the builder to build what the designer/architect drew and calculated the boat to be; from the simplified set of 'lines'.

The lines of a boat are the projections of a series of hull intersecting planes onto the three flat planes shown in these illustrations. I'll say that a different way; each of the three views holds a series of outlines of the shape of the boat at a plane parallel to that view plane; the outlines of intersection are "stacked up" on that view.

The lines are like a geographic contour map or a soundings chart; however, only the Plan View is like a map but the idea of stacked contour outlines is the same in all three views.

more confused than when we started? lets try some more images.

cheers,
Kevin Morin

[kmorin]

To continue this look at the hull's lines lets begin with the idea of projection.

here is the shadow of the dory outline on the back panel labeled Profile View; the shadow is the green outline on the
back panel labeled Profile View.


Here the same idea of a light shadowing the dory onto the bottom or Plan View, and this shadowed outline is shown blue.



The problem with the light is the shape of the boat is distorted somewhat but the idea is exactly what we'll see is used to 'project' the hull's lines on the three view planes.

here is the first example of projecting the lines of the real boat onto the Profile View [page]. Unfortunately I made this illustration form a poor point of view, the after most keel projection point coincides with the corner line of the Body Plan View plane and the Plan View plane so that line is confusing- and we're viewing it through the translucent dory as well! Oh well the bow/sheer point shows well as do the forefoot stem point and one at the lowest point of the sheer line amidships. The idea in this image is that each of the lines of the outline of the centerline or keel plane is projected straight to the Profile View.



this image introduces the 'unspoken' planes of glass that are the hull intersections. A gray pane of glass is located in the keel plane of the dory. The lines of the previous image that are projected onto the Profile View are those points on the hull that intersect this plane. So the Lines are 'Stacks of outlines at various Planes through the hull'.



In this image the plane of glass was made opaque to correspond to the outline of the hull showing through on the right or back side of the Profile View. It's important to note that the actual shape of the side panel is NOT being shown, just the OUTLINE of the side panel at the intersection of the Keel Plane to the Hull. [In order to figure out the side panel's flat layout is a different discussion entirely!]



This begins the projection of the outline of the boat looking down, or the Plan View of the boat. Here all the lines have been projected straight down one to the flat plane below call the Plan View plane.



In order to make the previous sketch more informative here is a view of the projection lines withOUT the dory. Its important to remember this is not how boats are designed, they are drawn in the three views, they WERE drawn in the three views, but we're starting with the finished dory and working backward to more easily explain the lines' relationship to the hull shape.


next, we'll continue looking at the planes through the hull and their projections onto the three Views.

cheers,
Kevin Morin

[kmorin]

We've introduced the idea of projection of the hull onto flat planes behind the three Views of the boat, bottom, side and end views. We called them Plan View, Profile View and Body Plan or Section Views, and we'll continue looking at these outlines in this post.

This shows a pretty complex set of image lines where the dory is a translucent gray 3D shape in the foreground with the projection lines connecting the outline of the dory backward to the Body Plan plane.



To simplify that previous image by reducing the visual information, our point of view is now more above the stern area, and we can see the projection of the Plan View on the bottom plane below the boat, the Profile View on the right side of this view and with some study you may pick out the projections of the various hull (out)lines on the Body Plan View panel aft the hull.



The dory is gone, the projection lines are gone, and what is left may look more familiar if you've spent time looking at Lines Plans? Here is the outline of the dory's three main Views. This is [more] what a Lines Plan, for a simply dory shape, looks like when it comes from the designer or plans service.



I think its important to remember that the lines drawing describes a hull's shape and we're looking at PC based 3D models of an explanation of those drawings. The sketches are my attempt to make it more clear what information is presented in a lines drawing not how they're made.

Cheers,
Kevin Morin

[kmorin]

In 2d drafting on paper you can manipulate lines of flat surfaces more easily than you can 3D shapes. By using flat planes to intersect the hull model shape the draftsman/designer could more easily explain the shape of the design where it could be measured and recreated by others without resorting to complex 3D drafting techniques.

In this post we'll look at the 'sets' of lines that are 'cuts' through the hull. Earlier we'd mentioned that Hull Lines are 'stacks' of outlines of planes intersecting the hull. There are three groups of planes cutting the hull. Each group is parallel to one of the three Planes we've already introduced where; Body Plan planes are Stations or Sections; Plan View planes are Waterlines or Waterplanes, and Profile Views are Buttock Lines or simply Buttlines.

In this illustration an imaginary series of glass planes are shown stacked up, cutting through the dory model hull, all parallel to the back plane of the Body Plan View plane. These planes are called Stations Planes or Section Planes and they are all 90 degrees to the Plan View and the Profile View.







if all the glass plates have an outline of the dory at that 'station' along the keel, and they were stacked together, we'd see the stations all 'stacked' on one sheet- the Body Plan.

Cheers,
Kevin Morin

[kmorin]

Next, this stack of glass planes are parallel to the Plan View so they are aligned to the floating waterline and are called Waterlines, or Waterplanes. Each different point of view of this image shows the glass waterplane cutting through the hull. I have not drawn each waterline's projection onto the Plan View, but from the outline view projection you can see what is done for each 'Plan View Cut' along the hull.


Actually it would be better to call these waterplanes' instead of waterline lines, since they are in the plane of a waterline, but the waterline is the plan view of the outline of the dory shape as it intersects the the hull on this plane- or waterplane.


the true waterline is the curved intersection of the horizontal waterplane (darker green glass) and the lighter green hull.


image here is a little fuzzy due to low resolution settings but we can see the curved lines of the waterlines' port sides along the red inner side of the dory.

Last, these planes are called Buttocks or Butt Planes and the lines they project onto the Profile View are the Butt Lines.





Finally a view that shows each set of the planes as they all 'exist' in our imagination, but we seldom take time to draw! Each set of planes or cuts or intersections through the hull help to more exactly describe the shape of the hull. These illustrations all involve a very simple dory shape so that the complexities of compound curved surfaces didn't make the underlying ideas harder to see. The dory used is made of flat sheet material that will come out of plywood, metal sheet, or any other flat material but that isn't true of rounded more complex hull shapes so they were excluded to make our discussion of the basics of lines more easily illustrated and explained.



There are numerous sources of this information, probably all better than this one, most of them in copy written books that I didn't want to bother asking to re-publish or reprint this section of those many books. Some of the best illustrations are by Sam Manning a regular at the Wooden Boat Magazine and in many books, others' treatments of this subject include Wm Garden, Dave Gerr, and John Gardner to name only a few, all highly recommended.

We didn't address the diagonal lines planes here because they're mainly used in rounded hull forms for blow boating, and we're more focused on hard chine planing hulls.

Cheers,
Kevin Morin

[kmorin]

To conclude the original claims that the lines were a 'stack of outlines' we need to image a series of glass planes passing through the hull. We see on these glass planes an outline of the hull cut intersecting with that plane.

If the plane is flat to the water then the shapes on the horizontal stack of glass planes/panes is (like) a series of waterlines, and if the planes pass through the keel at 90 degrees, but stacked from 'front' to 'back' then they're parallel to the Body Plan view at the 'back' of the boat in our illustrations. If the glass planes are parallel to the keel plane but offset from the center they are the Buttock Planes and show the Buttlines as intersections along the hull model's surface.

IN EACH CASE the stack of lines is projected onto a page, flat to the paper, and the projection of all those planes is ASSUMED of the viewer. Since ASSUMPTION is my favorite form of 'logic' and I get caught in its trap all the time I'd like to avoid that here. I wanted everyone to see those glass planes where the actual intersections happen.

This image shows a view of the dory we used for the 3D illustrations (well a closely shaped dory) as a Lines Plan.



In many Lines Plans the Body Section or Body Plan (middle of the page) is shown half&half. The right side of the Body Plan is the forward half of the boat and the left half is the after half of the boat. I thought that was confusing so I've shown them both, one from the 'front' and one from the 'back'. Notice that in each view the other cut planes are shown on EDGE therefore as single lines located at the edge of that cut or intersection plane? There is no perspective in a set of Lines, there was perspective in the 3D illustrations to make them more clear- I hope.

Also common but not shown here, is a Lines Plan where all three sets of lines are superimposed on one another. This version requires more experience to read or 'see'. Just like folks who are able to convert little black dots and lines on paper as sounds and even beautiful music, the lines of a boat are a 'graphic convention' or standard way of viewing a marine hull shape. This view can't be understood well without study any more than reading these lines could be learned without similar study and practice.

My purpose here has been to help create a series of images to make the ideas of Lines Plans more understandable to those just beginning to study them. If you have any questions about this post please let me know- it won't be of much help if it doesn't make sense or confuses instead of clarifies these graphic conventions.

I wrote the article to help a friend who was looking at lines but didn't 'see' what was shown of the hull forms. It has been posted at MetalBoatBuilding.org and may have circulated elsewhere, it is presented here to help metal boaters to give adequate attention to the graphic conventions used to show a hull in traditional drawings.

When you look at or discuss the performance and handling of a boat, using the shape of the lines of that hull will help make clear why one or another characteristic is present or absent in the hull's motion.

Cheers,
Kevin Morin

[welder]

Kevin, this is a wonderful post and moved it to, HELPFUL INFO forum.

If you can not post there let me know and I will make it happen.