What are all of the lines on my drawing of a ship?

Ship plans are particularly confusing because there almost no straight lines in the ship itself! Here are a typical set of plans - almost all of the straight lines are reference lines! (These plans are of H. M. Schooner Union, a center-board schooner used in the suppression of the slave trade, dated 1823 (these drawings are based on ones from Howard I. Chappell's The History of American Sailing Ships):

Notes:

If you find these images too small, click on them to get a much larger copy of the image that you can print out and compare with the text.
I've added color to help identify particular points.

There are several views shown on the plan: a side view (called the Profile), a top view showing the Waterlines (the Plan; here, below the Profile), a similar view showing the Diagonals (at the bottom in this plan, overlapping the Plan view), and a view as seen from the end of the ship (the Sections - here it appears in the "upper left" of the plan.).

You'll find a "bar" between the Plan and Profile views - this is the scale! It consists of seven equi-spaced parallel lines, crossed by other lines which are numbered 0, 1, 2, ..., 10, 20, 30, etc. These mark off feet! There is another division before the 0 mark (at the right end in this example); this has a "V" in it, which has the effect of dividing the 7 parallel lines into 12th's - use this to measure inches!

Lets start with the Section drawing. It displays the edges of a series of slices through the hull perpendicular to the longitudinal axis. The outside perimeter corresponds to the widest part of the hull; this is traditionally labeled as 0 with a slash through it. It show two different views; on one side is a set of lines toward the bow (traditionally labeled with letters A, B, C, ...), and the other side a set of lines toward the stern (traditionally labeled 1, 2, 3, ...). These are called Station or Mould lines. Some may be missing (typically those which would be too close together because the hull is not changing rapidly at those points. I've marked one of these slices "Orange", with "Red" edges to the Orange slice. The Orange slice is also marked on the Plan and Profile views; note that the edges are straight on these views - they correspond to the actual slicing cuts. Now look at a 3-dimentional view of the entire hull:

In this view you can see where the Orange slice lies on the hull.

A succession of slices parallel to the Plan will appear as straight edges on the Profile and Station views; they result in curves on the Plan view. I've marked one of these slices "Blue" with "blue" edges, corresponding to the cuts; locate these on the 3D view. These are called Waterlines.

A succession of slices parallel to the Profile will appear as straight edges on the Plan and Station views; they result in curves on the Profile view. I've marked one of these slices "Green" with "green" edges, corresponding to the cuts; locate these on the 3D view. These are called Buttocks.

Finally, on the Section view you'll see a set of diagonal lines; these are called the "Diagonals" (see What are diagonals used for?) These are used just like Waterlines to locate the shape of the hull; they are used because they tend to fill in areas where the other lines are broadly spaced.

These views also include other details: the shape of the rudder, stern, keel, head timbers, wales (if present - Union doesn't have any), moldings, chain-plates, and - on this ship - freeing ports, cannon, and centerboards.

If you are lucky, your plan will contain some other information:

This view shows an Inboard Profile (a slice through the center-line of the ship, showing internal details hidden by the surface of the Profile view; objects insidethe bulwarks are shown too). It also shows a Deck Plan (useful for locating hatches, cabins, guns, and other objects on the deck.
{John O. Kopf}

Note: if you like this vessel, the lines have been converted to a pair of images that will print at exactly 1:96 (1" = 8') scale , and can readily be converted to other scales (on most printers, these will be multi-page output that you'll have to "stitch" together to make a working drawing); there's also a third (unscaled) image giving some idea of the sail plan. These are:

(208KB),

(124KB) and

(46KB).

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