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Charles Green

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  1. My boat building experience is limited to the making of racing canoes. No decks there, not on the ones I was involved in, so while in that endeavor the deck-beam, camber question never reared its head. My experience with model ship building is limited to 18th century ships-of-the-line. At model scale, their relatively straight sides and minimal deck shear make this issue inconsequential. Early on, Andy Davis (Wooden Boat #165), now a naval architect, was involved hands-on in the making of dozens of commercial vessels with deck beams made to a constant camber and encountered the deck distortion this method produces every time. I contacted him recently and he allowed me this quotation: "There is no controversy, just geometry. Applying curves cut with a constant curvature to a random, three dimensional curve in space (e.g., the sheer) will not form a "fair" surface. The change in surface curvature increases with curvature of the base curves; hence, the error for a historic, bluff bow merchant ship with large camber will be greater than for a modern racing yacht with little camber. Prior to modern methods for developing a deck surface, the only way they had to do it was with deck constant curvature beams...maybe it is therefore historically correct. No modern fiberglass yacht builder would construct the deck using single camber deck beams. I stand by the accuracy of the article." In post #32, the white cookie-cutter shape, and immediately below it, the three dimensional drawing of the deck surface it is a projection of, raises a question in my mind. A piece of paper, cut to the shape of the cookie-cutter, flexible as it would be, would not fit on the three-dimensional deck surface. Not unless it were elastic. The area of the 2D projection is less than the 3D surface. The 3D surface could not be built from material cut to the shape and size of the cookie-cutter. Though both drawings represent the same object, they aren't the same. For construction purposes, are they relevant to each other? Do these drawings assume elastic properties that building materials do not possess?
  2. I recently ordered a number of books by David Antscherl from Seawatch. When I got to the stage in the ordering process to "push the button" and place the order, it didn't appear that the transaction went through. I tried a number of times with the same apparent result. The next day, via e-mail, Seawatch contacted me and inquired about the multiple, identical orders I had placed. It turned out that each attempt at ordering had been successful, resulting in an enormous bill! On my behalf, Seawatch went to work immediately, straightened things out with my credit-card company and I received my order today, one week after placing the order.
  3. On modern steel vessels known to have been built with all deck beams of the same camber, especially warships: For the sake of economy and fast construction, a uniform camber makes sense. Is there any evidence of the use of shims or some type of adjustment on the beams at the points of deck fasteners to fair the deck? During repair and refits of historical vessels, when deck planks have been removed, does anyone know of finding evidence of shims or wood removal to make the original deck fair?
  4. Ladies and Gentlemen: Remember, I am only the messenger! The message comes from Andy Davis's article in Wooden Boat #165. The illustration in post #26 is present in Davis's article as well. It's even on page 112 of Chapelle's Boat Building. Following, is what Davis has to say about that method of laying out camber..."In reality, this method produces a curve that is not even a particularly good approximation of an arc in that it does not have uniform curvature and is about 5% inaccurate relative to a true arc. Nonetheless, it is generally in boatbuilding books as being more accurate and technical - it is neither." Now, on to my own observations of the CAD drawing in post #24: Near midship, where deck beams begin to be represented and looking to the bow; the first Red line representing a deck beam makes a perfect intersection with the Black shear line and with the vertical Red line descending from the Green line. The vertical Red lines are important. They represent the distance the Black shear line is from the Green line; the Green line being a straight line drawn from the point where the deck meets the bow to where the center of the deck meets the transom. The curve of the Black shear line is a function of its intersections with the vertical Red lines. And the Black line is a smooth, fair curve. To create a fair deck that follows the curve of the Black shear line, the intersections of the Red beam lines with the vertical Red lines must agree with the intersections of the Black shear line with the vertical Red lines. And as stated above, looking forward, the first Red beam line and the Black shear line intersect the vertical Red line at the same location. At this location, the Red beam line and Black shear line are in agreement. Now, go to the second beam forward. A tiny discrepancy can be seen in the intersection of the Red beam line with its relationship to the Black shear line. It appears low; maybe too close to call. Go the the third beam forward. The discrepancy between the Red beam line and the Black shear line is greater. The Red beam line definitely lies below the Black shear line. By the seventh beam forward, on my computer screen, the Red beam line's intersection with the vertical Red line lies about 1/8 inch below the Black shear line's intersection with the same vertical Red line. With the next Red beam line, very near the bow, the discrepancy begins to correct itself. This is exactly the problem created by deck beams all made to the same camber as described by Davis, and this drawing proves his point. The same type of distortion occurs in the aft section of this drawing. With deck beams all cut to the same camber, the intersections of the Red beam lines with the vertical Red lines cannot match the Black shear line's intersections with the same vertical Red lines. On a deck made of beams all cut to the same camber, the amount of distortion, as built (the Red beam lines), compared to the shear, as designed (the Black shear line), is variable, depending on the amount of camber, the rate of taper of the bow and stern and the amount of shear as shown on the shear plan.
  5. CDR_Ret: This is a case of "a picture being worth a thousand words", but the picture in question is copyrighted and I don't have the skills to electronically transfer an illustration from one place to another anyway. So bear with me. Imagine laying deck beams, all with identical camber, in a hull with fore and aft taper but designed with no deck shear. In other words, the mid-ship deck beam shown curved (cambered) on the body plan, with the centers of all the others lined up on the water-line plan, creating a flat/straight deck on the shear plan. And, consider the geometrical theory stating circles/arcs are composed of an infinite number of straight lines progressing around the arc's center, all tangent to the arc at its radius. In other words, circles/arcs, are composed of straight lines. Delving into matters of infinity isn't necessary for this discussion, but in this example, as the beams approach the tapering bow and stern of this hull, they become shorter, and since they are all made to the same radius, their curvatures begin to approximate a straight line. This is to say, as the beams shorten, the high-point of their camber will begin to approach the same height as their beam ends. On the shear draught, this vessel has no deck shear. But as-built, with all beams made to the same camber, it will have deck shear, and a strange one at that. The high-point of the mid-ship, deck-beam will be the high-point of this deck's shear. From that point on, 'though the beam ends are all mounted at the same height above the keel, the height of their centers will create a down-hill taper, 'till at the bow and stern, the height of the beams' mid-points will approximate the height of their beam ends. On a vessel with a tapering bow and stern, designed with deck shear and with all beams made to the same camber, the tapering distortion described above will show, as-built, as a dip or depression in the designed deck shear as the deck approaches the stern and bow. The only way to get around this distortion on a deck built with all beams of the same camber, is to sequentially elevate the clamps to keep the beams' centers on the designed shear line. As far as I know, this is never done. And it would create another type of distortion on the deck near the beam ends. Davis states no conscientious builder would produce a deck with a swale on each end. And indeed none do. But the use of strong-backs, shims, the shoring of low beams and planing off the high beams at the transition is work that must follow to be able to make these beams lay a fair deck. A sliding batten, as described and illustrated by Davis is a way to lay out a distinct camber for each beam that will lay a fair deck.
  6. I recalled an article in Wooden Boat magazine that addressed this topic. It has taken me this long to find it - "Deckbeam Moldes - Ye Olde Mythe of Boatbuilding" by Andy Davis, Wooden Boat, #165, April, 2002, pp., 40 - 45. The answer is, in order for the height of each beam's crown - at center-line - to match its height - as seen on the shear draught - each beam must be made to its own arc. The "constant camber" approach will only work on vessels shaped like barges, with parallel sides and no shear. Davis outlines several "tried and true" methods for establishing a uniform arc for all of a vessel's beams and shows how they all fail to produce a fair deck. Davis describes how a fair deck will only result from these methods after shaving and shimming to make up for each methods inaccuracies. Davis also describes a sliding-batten method for establishing each beam's curve, that will result in a fair deck. On a vessel with deck shear and tapering ends, the inaccuracies of a constant camber show up as a dip in the stern and bow areas of the deck. At model scale, you might be able to live with it. It all depends on the model's scale, the degree of bow and stern taper and the amount of deck shear.
  7. To all above: In the past, had I not used all the methods (and more) I mentioned, when working on projects on a board in my lap, I would not have put myself in the position to advise them to anyone. The point not stated is, the lack of a tool has never stopped me from getting from point A to B. Much time and patience was used in stead, but I always got what I wanted. I enjoy the many diversions into the part making process as much as the build itself.
  8. Ed: In the category of power tools - none are needed - look at what the modelers of antiquity accomplished without them! Power tools are time-savers, no doubt about that. And, if your set-up is wrong, power tools will also allow you to ruin amazing amounts of wood in no time at all. Uniform widths and thicknesses can be achieved by making a sanding or scraping jig to stop the process when over-sized, hand-sawn parts reach the proper dimension. A jig will also allow uniform spacing of holes or making multiple parts that must appear identical. A high quality dial or electronic caliper will let you know when you have reached the dimension you are looking for. Even with power tools, there will be times when a jig will be necessary to get what you want from them. Sanding or filing surfaces flat can be made much easier by counting a number of strokes, turning the work 180 degs., and then using the same number of strokes. Then repeat the process as often as necessary. While shaping a part, always secure it in a vise or clamp it down or temporarily glue it to a substrate. Making jigs is a problem-solving endeavor. It also takes time way from actually assembling your model. But, with or without power tools, your modeling prowess will increase with your ability to make jigs and I believe it is a necessary skill to possess. After a while, you will be confident in your ability to make anything. Hand-tools: a down-sized version of the coping saw, the jeweler's saw, with appropriate blades, will allow cutting the finest of scrolls and curves. I prefer coarse-cut jeweler's files over sanding sticks for most small-scale finishing. Don't try small scale detail with a type of wood that isn't up to the task. Pear (or other fruit wood), box or holly are well suited for this purpose. Pear (as well as box and holly), has uniform color. The grain/color contrast of other fruit woods may be a detraction.
  9. Research has been done on the jelly sandwich/floor mess probability. Aerodynamics and rotational inertia guarantee that a slice of jellied bread pushed from a standard-height counter will land jelly-side down. In order for the slice to have time to rotate 360 deg., it must fall from around 11 feet.
  10. If the parts are to be glued, the wax must be removed. Scraping most of it off followed by immersion, agitation and rubbing in hot soapy water is effective. One of the many organic solvents may work but test before relying on it to clean your parts. Depending on the type of acrylic the solvent may damage them.
  11. There are "no melt" blades for cutting acrylic but their tooth-count is too course for your job. You will need a fine tooth blade. You can avoid the melting problem with any type of blade by melting a drop of wax or paraffin onto the acrylic at the cut site. Heat from the blade's friction will melt the wax. The melted wax will provide enough lubrication to keep the acrylic from melting. When ripping a long piece, melt wax along the cut line to provide continuous lubrication.
  12. Tung oil's advantage is that it dries to a harder finish than most other drying nut or seed oils. Blond walnut is the sap-wood from the walnut tree. Once under the bark, walnut's sap-wood can account for nearly 1/3 of a log's diameter.
  13. Don: Look into MSC Industrial Supply under the categories of slotting blades and jewelers blades. You will find an enormous range of blades made of HHS or solid carbide of any tooth-count, thickness, diameter and arbor size you could want. $25.00 minimum. You must establish an account - just contact info - no cost.
  14. I'm in the process of of filling a small bit of damage on walnut. I've got regular Titebond III and Titebond II Dark Wood Glue on hand. Mixed with sanding dust from the part being repaired, the TBIII dries too light and the TB Dark dries too dark. I'm experimenting with mixing the two glues to get the shade I want. A 50/50 mix is close. I'll try TB II, one part and TB III, two parts. Sooner or later, it looks like I'll get what I want. With sanding dust taken from the part being filled, this method should work for any color of wood.
  15. Pretty simple - use a sanding block. Strokes must one-way, towards the hull, so as to not lift any grain off the surface. Careful to not strike the hull and reveal the second ply.
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