|This is our initial set up for the "How To"
Section. It is continually evolving and being refined. If you have any questions, please
We often fear that which we do not understand. This explains the grimacing and rapid flipping of pages that occurs every time a prospective boat builder encounters a Table of Offsets. And you can not blame him. For, to look upon this extensive block of numbers, numbers without labels or explanation, for the first time is confusing to say the least. It causes about the same sensation as when, for no apparent reason, you took apart the radio as a child. A multitude of totally foreign objects stared back at you in a strangely organized lump insisting, against all your natural instincts, that they made sense.
But this block of numbers is nothing more than the conglomeration of many simple parts. As such it presents a simple problem when unraveled one step at a time. There is nothing intuitive about it, however, and the method of decoding must be learned. If you are fortunate enough to know someone who can explain first hand how it is done, force him or her to do so. If you have no such luck, there are many well written pieces on the subject that you can refer to, many of which will leave the beginner in doubt until he or she picks up a pencil and gets to work. Many times this alone will solve the mystery fall away and expose the simplicity of lofting. For that reason, this discussion will be broken down into a basic procedure to be used in conjunction with your own good sense.
Space is the primary consideration when lofting. The amount required is at least several feet more than the length of the boat one way, and a few feet more than she will be from the top of the stem to the foot of the keel in the other direction. The floor should be as flat and smooth as possible. Once an adeqaute space is found a drawing surface can be prepared. For this heavy white paper can be laid out if there is no moisture, or plywood panels can be butted together and painted white. If wood or concrete, the floor itself can be painted white and the lines laid down directly on it. We do not recommend the living room floor, not so much because of the damage you might do to it, but rather, because we believe the amateur has, and ought to exercise, the right to retain a haven wholly away from the project.
Having found a suitable space to start laying down the lines, it is time to gather the necessary tools and equipment. The essentials are a steel tape, battens and pencils or crayons of some sort. The tape should be of adequate quality to ensure accuracy. The battens are rectangular strips of clear, straight grained stock, of various lengths which will be used to produce the fair curves in your drawings. Take care in choosing these and have at least a few handy. For drawing the lines any type of pencil will do though colored pencils may be useful to avoid confusion later on.
With all this collected around the lofting floor you are ready to begin. Before looking at the offsets begin to lay out the grid by measuring up from the bottom of the lofting floor to a point with enough space above and below it and mark your Load Water Line(Do not ponder the word "load" here. The LWL is simply the designers projected waterline. It will be one of your main points of reference in the lofting procedure.) Since this is to be the key line around which your graph , lines drawing and then molds will grow, take extra care in making it true. perhaps the best way is to stretch a piece of thin line, fishing line or some good small-stuff, between two points and mark directly underneath it at steady intervals. Then connect these dots with your best batten or straight edge.
Next you will need to make several lines parallel to this one both above and below it. If yours is not to be a keel boat only one or two lines will be needed below the LWL. The intervals at which you are to place these lines should be clearly stated in the plans. All of these horizontal lines are referred to as waterlines.
The vertical lines in your graph , which are called, "stations", can now be drawn in at intervals also taken from the plans. Place one directly in the middle of your floor and work out from it. This will be your centerline. The best way to make these is using dividers and the intersecting arcs method of squaring a line and a long srtaight edge. Once all of these are complete and square you should have a graph that will allow you to faithfully replicate the lines you now see in the plans.
Referring to the Table of Offsets, the three sets of numbers which occur in each individual box indicate feet, inches and eighths of an inch respectively.(ex. 01-02-04 = 12-4/8") Each column will be designated a station and the rows will be labeled either heights or widths/breadths. Heights will be measured up or down along the designated station a specified distance from its intersection with the LWL. Alternately, widths will proceed along a given waterline for the specified distance from the centerline. Measureing and mark the distances in the table. If at any point something does not seem correct or clear, stop and take the time to figure just what's wrong. Also, remember the hard fact that although mistakes do occasioally occur in the tables, far more often the mistake is the builder's.
Before you wind up with a floor full of indecipherable dots, it is wise to go ahead and fair in the lines more or less as you go. Otherwise you may be measuring many of the points again just to figure out whats what.
With the lines laid out in full and hopefully looking more than just vaguely like those in the plans, it is time to begin making molds. First, however, be absolutely sure to check whether the lines you have drawn represent the inside or outside of the planking. If they show the outside dimensions of the hull it will be necessary to correct your lines in one more simple procedure before putting together the molds. Take a pair of marking dividers and set them carefully to the required thickness of the planking. Then make a series of archs on the inside of the line. Use a batten to trace a line tangent to these archs and create your molds around this new paralell line.
Spiling is one of those great tricks every amateur boatbuilder should know. Not only does it allow you to create new planks quickly, easily and with a great degree of accuracy, but also makes you seem very clever and skillful to the uninitiated. You might feel that way about it yourself.
Spiling is used to plank a boat from scratch, replace a plank, shape bulkheads, or any other task which requires one piece to fit tightly within the confines of others. To do this you will need a pair of marking dividers, battens such as those used in the lofting process to draw a fair curve, and one more item called a spiling batten. This is any flat, flexible piece of stock ,such as plywood or a plank planed thin, that will fit inside the space to be filled with at least an inch or so to spare all around. Pieces with a slight curve cut into them may fit into place better than straight ones when wrapped around the frames.
If you are repairing an existing hull, as I will assume for the sake of consistency, remove the damaged plank and clean all the exposed edges of the surrounding planks thoroughly. Find a suitable spiling batten for the task at hand and clamp it in the space from which the plank was removed. None of its edges should be touching the adjacent planks and it should lay flat and easy against the frames. Using your dividers, place the point on the inner edge of a nieghboring plank and scribe an arch onto the batten. Make absolutely sure that the dividers remain at a constant setting during the entire operation. In fact, go ahead and mark the distance you want between the points somewhere on the spiling batten for reference. Continue scribing archs from the inner edge of adjoining planks until you have completely circled the missing plank. Scribe more archs where the curve is tighter and one from the point of each corner.
Now remove the spiling batten from the hull and clamp it down on top of the piece of stock you have chosen for the new plank. Check the end grain of the stock to be sure that any cupping opens downward on what will be the inside of the plank as this is the way all planking should be fastened to keep the hull fair as the plank begins to soak up water and expand.
To transfer the marks on the spiling batten to your stock, place the point of your dividers on an arc to one side of its apex and scribe a small line on the stock. Move the point of you dividers now to the other side of the same arch and scribe another small line intersecting with the first. Do this for every arc on the batten. Remove it and connect the points of intersection with a straight batten or other limber straight edge to outline the shape of your plank. To cut out the new plank use a skill saw set to cut just over the depth of your plank. Leave a little extra outside of the line to be trimmed with a hand plane later if you like, but try to make your original cut as carefully as possible. Soon you may be able to come up with an exact fit right out of the gate.
In addition to all of this, some people advocate flipping the spiling batten and marking the plank on its inner side. The reasoning for this is that, since the measurements were taken off the hull against the bare frames, it is the inside of the plank that is being measured and , therefore, that should receive the cut. This is correct and an especially useful tip when planking bigger boats with thicker planking but probably unnecessary when repairing production or smaller boats with thin planking. The process is not difficult, however, and you may find it worth the extra step. To do this, simply drill holes through your spiling batten at opposite ends of each arc as discussed above. Flip the batten over and place it on the inside of the plank , as dictated by the cupping of the grain. Scribe the intersecting archs and cut.
Lamination is an effective technique and a credit to modern technology. In many of its forms it is also compatible with traditional restorations. Stems, keels, frames and other solid structural timbers can be conveniently manufactured in this way when no single piece of suitable stock is available. Also, laminated pieces are stronger and more rigid than their sawn or scarfed counterparts. For these reasons and more, it is a popular technique used in just about every corner of the wooden boat industry and one of which every aspiring or amateur builder should have a working knowledge.
Other than wood , the two things absolutely necessary to create a laminate are epoxy and clamps. In the epoxy look for quality while sheer numbers can not be beat when it comes to clamps. If the piece to be glued must contain a curve of some degree, a jig or "duckboard" must be built. This is done by tracing or otherwise laying out the curve on a piece of plywood then attaching a series of blocks, "ducks", along the line. The strips will then be pressed and clamped against these blocks so it doesn't hurt to oversize them a bit.
Understand also that a laminated piece is one that is composed of a series of thin strips stacked on top of each other with a layer of glue between each. The large amount of strength in such a piece is taken from both the adhesive and the directional continuity of the wood strips. Two pieces scarfed and glued together might make a strong enough timber for certain applications but does not constitute a laminated timber and should not be substituted where construction calls for one.
When you are ready to glue, prepare a surface of tin foil, or wax paper to keep the piece from being glued to the floor or jig. Make sure that the wood is clean and dry. The goal now is to have the whole mess glued and clamped tight as quickly and cleanly as possible. Rubber gloves may help to do this by eliminating any concerns about gluing fingers together. Think through the process and have everything at hand. As soon as the epoxy is mixed, smear a layer across the surfaces to meet with a squeegee or flat piece of scrap. If possible glue all the pieces together at one time and be done with it. If they are too big or too many to manipulate or if you run into a snag and fear the glue will begin to set before all the pieces are together. Make sure that these strips which were attended to are clamped tightly together in the correct position. The rest can always be added after they have dried.
Frame members made in this way can be shaped and faired after the epoxy has hardened. Drill, saw and shape them as you would any piece of wood, though perhaps not with those really fine edge tools. A grinder may be more suitable for dealing with the glue if any portions of any size need to be beveled rounded or removed.
Steam bending frames is an involved process best left to professionals and only the most experienced amateurs. That said, everyone has to learn sometime. If this is something you really want to do, take the time to understand the procedure, continue with care and be prepared for a certain amount of disappointment. Not every piece of oak you pull from the steam box will take the bending nor will you be able to bend every frame on before it cools. You will figure out that steamed white oak, while amazingly flexible, is not as soft as an "over cooked noodle" and that you must manhandle it from the instant it is out of the box until it rests securely in place. If you persevere and succeed, however, you will receive for your efforts the satisfaction of creating or restoring a fine boatin great tradition.
The first thing to concern yourself with in this process is the steam box. If you do not have access to a good one and your project entails more than the bending of one or two frames, it will be necessary to build one. To make it sturdy use solid lumber, one-by pine is good, and make it as long as you could ever conceivably need. Be sure to give it an adequate inside height and width as well when choosing the boards. Give it corner supports of square strips and fasten it all together tightly with screws or nails to ensurea minimum of leaks. Place tight fitting doors on one or both ends and hang them with heavy hinges. Use a heavy strap or rubber bungee to keep it sealed shut. Finishing touches can include a rack on which pieces can be stacked inside but these are not essential.
. For one interesting method of generating steam refer to Allen Taubes book The Boatwrights Companion (International press ETC ETC). In it he gives ample instructions for building a compact electric unit using a 220 volt hot water heater element and common household plumbing. The unit is less than 20" long and can be attached to the side of the box or carried separately for on-site convenience. A more basic method, though equally successful and the one we use, involves a small, one-burner camp stove and a pot of water. Simply clamp a tight lid on the pot, connect a length of rubber hose to it with a correctly sized through fitting and connect the other end of the hose to the top of the box in the same manner. Then it is just a matter of finding some matches and making sure that there is enough water in the pot to steam the wood for a sufficient length of time.
With this solid contraption, made from scratch to your own standards and for the express purpose of steaming white oak frames for your boat, you should feel confident and eager to proceed. The next step is to acquire some green, straight grained white oak. The wood should be green because dry wood is too brittle to take the stress of bending and straight grained because any grain runoff in the frame will cause the fibers to sheer apart without fail. Finding such lumber may be difficult but it is the only way to ensure any degree of success. Also, as you are collecting and cutting the frames keep in mind that the lines in the end grain should run as nearly for and aft with the hull as possible. They will be stronger this way and less likely to split when fasteners are driven into them later.
With just a little more preparation you will be ready to begin. This must be done on the boat. Be sure everything is correct and cleaned up so that nothing will hinder you while racing to slide the frames in place before they cool. Mark points of reference for each frame so that it will be put in the exact place it belongs the first time. If building a lapstrake boat and the planks are already in place or simply repairing your boat, have the fasteners sitting in pre drilled holes, flush with the inside of the planks so they can be driven in quickly to help secure the frame. If repairing a boat it may be necessary to remove a plank or two in key areas so that a clamp can be inserted to hold the new frame against the hull. Also realize that when repairing a boat, if the interior is open enough, a mold can be made into which you can bend the frame so that it can be fitted into the hull after it has cooled. This will allow you do a more careful job as there is no pressure to hurriedly drive in fastenings to hold the timber while it is hot.
When everything is ready to begin, fire up your steam box and throw in some frames. They will have to cook for an hour or more so take this opportunity to relax and think through every step of the process as well as you can. At the designated time, put on some heavy gloves, open the box and quickly yank out a piece, closing the door again after it. Run to the boat and hand it to a friend standing there ready to take it. He will then begin using both hands and possibly both feet (Im serious) to conform it to the shape of the hull. To do this, however he will have to exaggerate the bend some by hauling down on the top of the frame to allow for a certain amount of relaxation in the fibers as they cool. As he is locked in this wrestling match you should be securing the frame from the bottom up with either clamps or the fasteners already in place. If, in the course of this mad dash, the wood has proved itself worthy and yourselves certain and smooth enough in your actions, a strong oak frame with fair curves and without any fractures or splintering should result.
Since this is your first time though, do not be discouraged if you have missed the marks, failed to achieve an adequate bend, or broken the frame. Try to learn something with each attempt that will allow for faster, more efficient execution.
The adaptability of sawn frames to any hull shape has always made them a popular choice. This is especially true in more recent times as natural crook timber and wood adequate for steam bending has become scarce. Sawn frames are any in which two or more pieces are butted together to create a timber of the necessary length and shape. This can be achieved in several ways.
The type of sawn frames probably best known to the modern wooden boat enthusiast is the single frame. Used in smaller boats and V- hulls, this is the type of structure you will see in nearly all wooden power boats. They consist of straight pieces, called "futtocks", on either side of and butted at the chine. At the butt a another wooden piece is fastened over the joint to secure it. This is called a cleat or Gussett. At the keel the two bottom futtocks of a frame meet and are held together in a similar manner though the gusset is replaced here by a floor timber. The floor timber is bolted to the keel and extends out along either side of the frames, thus joining the two halves of the frames and securing them to the keel.
The other common form of the sawn frame, the double frame version, is generally used in larger round bottom boats. It operates on the same basic principles. Instead of using a simple gusssett or cleat however, the double frame method pairs one set of futtocks against another so that the butt joints of each are supported by the whole pieces of the other in alternating fashion. The benefits of double frame construction are a strong and potentially heavily curved frame. Some natural curvature in the wood grain is desirable in certain sections of such a frame but not enough to present a problem when locating stock. Floor timbers for the double frame operate in the same way as in the single frames, using one solid piece as a cleat where two other futtocks butt together at the keel.
Frames made of natural crooks, that is, which are cut out of a log which contains the correct shape for the frame in its natural state, might be considered a close relative of the sawn frame. They are cut from a larger piece and incorporated into the hull without changing the natural situation of the grain, but they are far stronger That is not to say, however that a properly built sawn frame is not strong, especially after it has become an integral part of the whole boat. Then the planks, stingers ceilings and so forth work together with the frames to produce a plenty strong boat as generations of fisherman I'm sure can attest. But there is simply no rearrangement of parts that can compete with the natural unchecked flow of the wood fiber for strength.
This is only the beginning!