Carving a Static Model Hull

Background

This message is in response to the question on the Seaways list about how to carve a hull, which I think is not only an important skill, but also an excellent way to develop "an eye for a ship," that is, an intuition for the form of a hull. The technique I will describe was taught me by a pattern maker and master model builder many years ago. It's one of those things that is a lot easier to grasp by watching and doing than to describe in words. I'll do my best, not with the idea of showing off or proposing a frustratingly high standard of craftsmanship, but rather in the hope that it may help others turn what appears at first to be a daunting task into one of great enjoyment. My experience is almost exclusively in carving "yacht-like" hull forms, but the technique should be of interest to carvers of "ship-like" hulls. (Well, maybe not supertankers, but certainly clipper ships.)

Laying Out

I will assume that you are starting with a typical "precarved" hull. I haven't looked at one of these in a long time, but I doubt that they have changed much: just a block of wood that has been hogged out by an automatic carving machine to a rough form around 1/8" to 1/4" larger in all dimensions from the final shape.

The first step is laying out a set of reference lines to use in forming the final shape. This is the first place to make a significant error (been there, done that, got the firewood to prove it). If you carve to a wrongly placed set of reference lines you can find yourself "running out of wood" somewhere along the line. If you visualize the final shape as a kind of phantom hull lurking inside that block, to be uncovered by carving away. You want that phantom to be in the middle, so that there is roughly an even amount of wood to be removed all around. Since you are carving from the outside in, if you place your patterns incorrectly you will be defining a phantom that is too high, or too low, or cocked at an angle (my favorite mistake) and there won't be enough wood left around it to produce the proper shape.

To draw these lines I prefer the Micron Pigma line of drawing pens that are sold in most art supply stores. These lay a very fine line with little or now pressure required. To position the lines you will need three things: a flat surface, a clamp or cradle to hold the block upside down, and a simple surface gauge. The flat surface can be any table or workbench. I find it is best to make a special clamp to hold the hull rather than jury-rigging something from C clamps or carpenter's clamps. The clamp should be capable of holding the hull inverted,on the flat surface, with the waterline horizontal. The surface gauge is just a block with a vertical piece of wood to which one of the pens can be clamped with a miniature C clamp.

The first line to draw is the centerline, which will run down the deck and along the keel line. A flexible plastic ruler helps here. When you have the centerline drawn all around the hull, check against the plan (top) view with calipers to make sure it is truly centered. Place the hull in the clamp and sight both stem and stern along the tabletop. The lines should be vertical; if they aren't, you have the keel line offset from the deck centerline. Sand the errant line gently away and redraw.

Now the most important line, which is the load water line (LWL). Lay the block on the profile (side) view, position so there appears to be the same amount of excess top and bottom, and mark the LWL on the stem and stern. Put the hull inverted in the clamp, and clamp the marking pen on the surface gauge at about the height of the LWL off the table. By a combination of rocking the hull in the clamp and adjusting the height of the marking pen, arrange things so that a) both the stem and the stern marks are the same height above the table and b) the pen is at that height. Then gently draw the LWL by running the surface gauge around the hull. Don't worry if you don't get a continuous line; you can fill in the gaps using the flexible ruler. Sight both stem and stern; the centerlines and waterline should be sitting nicely at right angles to each other. (Stopping periodically to admire one's work is allowed and even encouraged :-))

Now check the position of the LWL against the profile drawing with calipers. At various points along the plan, set the calipers to the vertical distance from the LWL to the sheer (deck) line. Then go to the same place on the hull and make sure that there is wood to spare above the sheer line. Perform the same checks with the lower profile line. As before, if it doesn't work out, erase the LWL with a little light sanding and redraw per instructions above.

Before we get to the last set of reference lines I have to explain the way, in this technique, a hull is formed.

The Form of a Hull

When you look at those nice scale drawings with the cross-section of the hull at each station, you are tempted to think that if you made a pattern for each station, carved to the pattern, and then sort of smoothed out in between, you get the "right" hull. Well, not necessarily. In fact, for many designers right up to modern times, the carved model came first and the drawings came second.

In the technique I am describing, a hull is defined by (usually) three "master sections." One of these defines the main or amidships body, another the "heel," or after body, and the the third defines the "entry" or the fore part of the hull. All sections between these are derived by a process called "fairing," which generates a smooth transition, free of bumps or hollows, from master section to master section. A carved hull is faired directly on the wood, by a process that is a lot like sculpture. When you do it, particularly for a hull which is of a "certain age," you are very likely duplicating the process the original designer went through, getting you closer to a "true" shape than any set of drawings can.

I said that fairing a hull was like sculpture, and like sculpture is an art, and like all arts no two people will do it the same. Yet after you do a few hulls this way you'll get a feel for it (and never look at a hull the same way again.)

So the final set of reference lines are the placing of the master sections. First you have to pick them out from all the sections shown on the station plan. The amidships section is easy: it's the biggest one. The fore and aft master sections take a bit of study, but for most hulls you can see where the distinctive form of that part of the hull is defined. In any case, it's no big deal if you're off by one station either way.

When you have selected the master sections, mark their fore and aft positions on the deck center line. With calipers transfer the half beams from the plan drawing to again make sure that there is wood to spare on either side of the hull. At each section positon, draw a line on the deck at right angles to the center line, then around the hull with the flexible ruler. Sight from the side. The lines running around the hull should be at right angles to the LWL. If not, yeah, yeah, sand off and redraw.

Now you've got a set of reference lines that postion that phantom hull right near the middle of the block. Carve away everything that doesn't look like part of a hull and you're done :-)

The Carving Process

To carve the hull you'll need the usual Xacto knives, a fairing tool, and a couple of battens. A fairing tool is a long, springy piece of material to which you attach the self-adhesive sandpaper used on small power sanders. A flat-surfaced sanding block is deadly to the fairing process; there ain't no planes on the kind of hull we're talking about :-) Using your fingertips is even worse. For the average (two foot or so) hull a thin, springy, 18" steel ruler is good. Battens are springy pieces of wood, say 1/4" x 1/8" model airplane spruce, used to check fairness and draw sweeping lines.

Make a set of patterns of the master sections. Xerox the plan, fold the copy in half carefully down the centerline, and cut both sides at once. Using a full pattern instead of a half pattern really helps get things symmetric. Glue to file folder card stock and cut out carefully. Make sure the LWL is marked on the pattern.

Draw the plan view on the deck. Don't cut a pattern from the plan -- for (usually) sweeping curves like this you'll never get it right. Instead, lay off the half beam distances for several sections. With pins (or better yet, a helper you don't mind being close to :-)) hold a batten in place to get the sweep of the hull shape and draw along the batten edge. Sight down the deck from stem to stern to check symmetry and if not ... well, you know what to do.

The order of carving and fairing is: amidships master section first, then aft, then fair the after body, then fore master section, then fair the fore body. Other sequences are possible, but they don't seem to give the same "feel" for how the hull is developing.

Carve to the amidships section first. Carve parallel fore and aft, so the middle of the hull looks a bit like a straight tube. Check with the pattern, making sure that you align the LWL on the pattern with the LWL on the hull. As you carve away parts of the reference lines, redraw them with the flexible rule.

Then carve to the aft master section. It's hard to describe how this looks; the closest I can come to it is that you carve at a straight angle from somewhere between the two sections, so it looks like a hull made out of two sheets of cardboard, one straight (the amidships section) and one conical (the aft section). Watch the deck plan so that you don't cut off a diagonal that should be an arc.

Now you are ready to fair the aft body. This is one of those things that is obvious when you watch it being done but tough to put into words. Anyhow, here goes: Put a little spring into your fairing tool so that it forms a gentle arc. Hold it at a 15 deg angle or so to the center line, and sand with a gentle curving motion so that you are forming a compound curve. Go slow. Do a little on one side, then a little on the other. Check by laying a batten along the line a typical plank would take. Sight carefully for bumps or hollows and work out with the fairing tool. As you get used to doing this, you'll see the hull form come up as if by magic, and your eye will be trained to recognize fairness when it sees it. Work it down to the deck line. It's not possible to perform *too many* checks with the batten :-)

The fore body is carved and faired the same way. If the hull has a "hollow" (concave) entry, like a lot of clipper ships and some yachts, then you may find yourself bending the fairing tool into a convex instead of concave arc.

The last thing to cut is the sheer line. On "yacht like" hulls, this is one of the most critical lines -- get it right and the hull is lovely from almost every angle, get it wrong and and the hull never looks quite like a boat. As with the plan line, use a batten instead of a cardboard pattern. Take the vertical heights from the LWL for several stations, and draw the line with the batten. Check by sticking pins on the line at station points and sighting from for and aft to see that they are at the same height. *Carefully* carve close to the line and then sand. This is the one point where a sanding block helps; especially the round-ended ones sold by MicroMark. Try to get a sweeping motion in your sanding. When you're almost there, switch to a scraper. Hold a wide Xacto chisel blade in your hand and pull it toward you with the ground bevel edge *away* from the direction of travel. This will shave a very small amount of wood from the deck. With a little practice you can scrape a sheer line to a really sweet sweep.

And that's it. One day you'll do a hull and it'll be so pretty you won't want to clutter it up with all that fiddely little detail (just kidding).

Well, I seemed to have rambled on an awful lot; as the old line goes, I regret I didn't have the time to write a shorter description. But I hope this conveys some of the enthusiasm I have for carving hulls, and helps you get started.

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