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First appeared in slightly different form in Cruising World magazine, September 1997, entitled "To Thine Own Chines Be True"Aluminum For BoatsCopyright 1997 - 2009 Michael Kasten Aluminum is a sheet material with virtues aplenty. To honor them best, I advocate simplicity, ample framing... and yes, even single chine hull shapes!

Why Build An Aluminum Boat?For things that go bump in the night. For ease of construction. For longevity. For good resale value. For the benefit of being able to create a custom design and build it economically, without the huge penalty of having to build a mold first, as with fiberglass. For freedom from the stench of fiberglass, and from the dread fiberglass boat pox. For repair-ability. For lightness and strength. For the competitive edge in performance. And most importantly, for the security of safe cruising. It takes over 60,000 pounds per square inch (psi) to tear apart a chunk of mild steel, and 30,000 psi to deform the same piece; to make it yield. With aluminum, around 45,000 psi will tear it apart, and around 35,000 psi will deform it. Yes, you read that correctly: size for size, aluminum has a higher yield strength. In these facts lie the extreme benefits of metal for hull construction: The "plastic range" of either metal is quite high, so the material can take a terrific beating without failure. Aluminum is light, strong, corrosion-resistant, non-sparking and weldable. Because aluminum is not abrasion-resistant, it can be cut with carbide tools. Aluminum is subject to electrolysis, pitting and crevice corrosion, but these liabilities can be managed as long as the installation of dissimilar metals and electrical items are correctly done. After that, it is a matter of attending to these matters during the life of the boat. In terms of seakindliness, some boat shapes may be better if built in steel. Aluminum's extreme lightness can introduce a faster pitching and rolling motion in some hulls. For example, very beamy boats will exhibit a gentler roll if built in steel. Fairly narrow or light-displacement boats, which tend to have a narrower waterplane and less inherent form stability, will benefit most from aluminum construction. These are of course generalizations. Given a blank sheet to begin a design, the roll behavior will be considered along with the choice of materials. In terms of size, one can successfully build a steel boat for coastwise cruising and serious blue-water sailing down to around 30 feet LOD. Below that, the steel vessel will either have to be built with excessive displacement or with quite thin plate that will be more difficult to build due to distortion while welding. An aluminum bare hull, built to the same strength standard, will weigh roughly 45% less than the same hull in steel. As a result, if high strength is of the highest priority, the aluminum boat can be built to the same structural weight as the steel vessel, and then be considerably stronger. We can therefore create aluminum cruising boats down to, say, 22 feet. One could still build a safe aluminum boat in a size smaller than that, but who'd want to go to sea in it? On CostThe aluminum to build a bare hull costs just under twice as much as the mild steel to build the same design. But aluminum is faster to work with, so the savings in labor helps even the score. The labor saved can be substantial since aluminum can be cut with common carpentry tools and is welded much faster than steel. Another significant advantage with aluminum is that there is no need to sandblast or paint the interior. You do have to insulate an aluminum hull, but that won't ordinarily require sandblasting. Painting the exterior of an aluminum boat is unnecessary, representing another big savings. After you've factored in the added costs of painting steel, the margin for building an aluminum hull drops to being a very minor amount when compared to building in steel. As a percentage of the entire construction project, the additional cost of the aluminum becomes very slight indeed. Once built, maintenance on an aluminum boat is less expensive, and resale value higher. These factors more or less even the score between the two materials. New construction methods have trimmed metal hull building costs substantially. The most dramatic savings can be effected by computer lofting, and then computer cutting the actual parts for the hull. Essentially, the builder receives a "boat kit" ready for assembly. A parallel method, also ideally done by computer, involves cutting and fitting the plate only, by itself, without a prior support structure. One last note about cost: When comparing like for like, boat costs tends to vary more or less directly with displacement (not length), assuming a given level of complexity in the design. Displacement, and therefore cost, varies as the cube of the overall dimensions. On Hull ShapeAesthetics are a personal thing. For my own part, I am attracted to the single-chine shape for metal boats because metal is a flat-sheet material. When building a boat using sheet material, it makes the most sense to think in terms of that material's characteristics and how one may optimize a hull design without incurring extra labor. In metal, a single-chine hull is easier and less costly to build than one with radius or multiple chines or one that is fully rounded. Further, with a good design there is no performance penalty with a single-chine hull. The slight gain in wetted surface, if any, can be offset by slightly greater sail area, made possible by slightly greater ability to carry sail due to the form stability provided by the chine. This line drawing and the ones that follow demonstrate degrees of design complexity for sheet materials, from single chine to a fully rounded hull. I prefer the simplicity and economy of a single-chine metal hull, as shown here. In my view, it is a more honest shape for a metal boat.

Further, the reputed seakindliness of a radius-chine or round-bottom hull can be approached in a single-chine hull by giving it a slightly more "slack" shape. A big advantage of the single-chine shape is economy; the cost to build a rounded or radius-chine hull is considerably higher due to the work involved with the added shaping and welding. A single chine can look quite appealing, especially when used with a more traditional style. In my view, it makes the most sense to take any extra money available and use this to make a graceful single-chine boat longer rather than radius chine or multiple chine, thereby netting some real speed and comfort benefits in other words, a bigger boat for the same money, with inherently greater speed potential due to the increased length. Multi-chine designs allow building with flat plate, without requiring that any plates be rolled. Although considerably more time consuming than a simple single chine, these shapes remain within the construction realm of the amateur or one-off builder.

Radius-chine hulls employ flat panels everywhere except for a narrow 'rounded' plate that joins topside to bottom, rendering a quasi-rounded hull without requiring that every metal sheet be rolled; only those at the radius. However... it will always be recognized as a radius chine vessel, and not a true rounded hull shape. Therefore if a radius chine is being considered, there is very little reason not to simply take the next step and go to a true rounded shape, as follows...

A fully-rounded metal hull is beautiful to behold. They need not be expensive to build if correctly designed, where only the minimum amount of plating needs to be rolled. These are not "radius chine" boats. They are instead just easily plated, rounded hulls with no reverse curvature, so these hulls can be built economically.

Radius-chine and multi-chine boats cost about the same amount to build, and a true rounded hull - provided it's designed correctly - need not be any more time consuming nor any more expensive to build than a multi-chine or radius-chine shape. And as a very big bonus... it will look vastly better!It is generally our first choice to make use of a single chine hull shape for metal boats. If for some reason a chine shape is not desired, we nearly always find that a well-designed rounded hull is the next best choice. It will share the same ease of construction as a multi-chine or radius chine vessel, but with a little bit of transverse curvature in the topsides and bottom. Designing true rounded metal hulls for ease of plating is not at all difficult. Our goal with a rounded metal hull is that the topsides and bottom will not require any pre-forming at all, there being just enough curvature to sweeten the appearance, but not so much as to require rolling. In other words, 90% or more of the vessel is still able to be plated using flat sheets, and without any fuss at all. One excellent technique when building a completely rounded metal hull involves using "joggled" plate seams, akin to "lap strake" planking in wood. According to this method, an offset is pressed in along one edge of the plate. The offset is just enough to take the thickness of the plate below it. Each plate is a strip about 12 to 18 inches wide. Bernard Moitessier's steel boat Joshua was built that way, and it certainly withstood the ultimate test...! Alternately, the plating can be lapped by instead jogging the frames to match the plate contour. Just above the lap, the frame jogs out to meet the plate above, etc. These lapped plate methods provide a much easier fit-up, and a much more easily achieved weld seam. If "lined off" nicely, as one would do with wooden planking, they can also look very good. The plate overlap creates its own longitudinal stringer and reinforcement. With any of these types including the fully rounded metal hull, as can be seen in each of the examples above, it is most economical in terms of labor if the keel is attached as an appendage. In other words given the strength of metal, there is no particular need to create a large reverse-curved garboard area merely for the sake of strength, as would indeed be the case with a glass or wooden hull. This saves an enormous amount of construction time, and is therefore the most practical approach. On "Frameless" ConstructionWith the notion of metal's extreme strength, we have come to a point of faith which has at times created a misconception: There is potentially misleading and incorrect information pandered by some in the implied promise of "frameless" metal boats. The concept of frameless metal boats is attractive, but flawed. The definition of "frameless" must be clarified Achieving the required strength in a metal vessel without using framing imposes an enormous weight penalty due to the required increase in plate thickness. If one applies well-proven engineering principles to the problem, one quickly discovers that frames are simply a requirement. Designers may employ devious strategies, such as using bulkheads, interior furniture or other features to achieve the required reinforcement, but responsibly designed and built metal boats, whether of steel or aluminum, definitely do use framing. Despite recent talk about "frameless" construction, responsibly designed and built metal boats do use framing. The added plate thickness required to forego framing completely would render a heavy hull indeed. Here, just three out of a total of 17 transverse frames for this design are illustrated.

Without the aid of metal internal framing, many metal boats are successfully plated, and the plating then is welded together prior to the addition of the frames. This construction technique renders a high degree of fairness. Other methods use a "folded plate" strategy, with perhaps one large plate per side, to make the plating much faster to erect. To give the vessel adequate strength in the final product, though, frames must be added before the hull can be considered finished. Many so-called "frameless" boats make extensive use of longitudinals, which, in "folded-plate" construction, are often pre-welded to the plate. Bulkheads or other internal transverse structures are used to reduce the span of these longitudinals. Strictly speaking, then, these boats do have framing, and with good design, the framing will be adequate to the task. Classification societies, such as the American Bureau of Shipping, Lloyds, and Det Norske Veritas are somewhat conservative in their approach, but working through their formulae demonstrates the benefit of framing, primarily to bring the weight of the vessel within a reasonable range while maintaining the required hull rigidity. Studies of failures in aluminum crew boats and offshore supply vessels show the need for being very conservative in terms of the allowable areas of unsupported plating, in terms of scantlings for framing, and in terms of the welding between frames and plating. Most often, the best framing style makes use of a series of strong transverse frames combined with longitudinals which provide the primary support for the plating. The longs, then, are held by the frames. In my view, the frames in a metal boat should always be located where required by the interior bulkheads. Bulkheads can then be bolted directly to these web frames, and all is as it should be, simple and strong. With a few tricks of the trade up your sleeve, an absolutely fair hull is the result. Some boats are built "Frames First" while others are built by applying the "Plating First" as described above. For further reading about the various advantages of each, please see our online article: Metal Boat Building Methods. On Protection And CoatingsAluminum alloys for use on boats are generally limited to the 5000 and 6000 series. These two alloy groups are both corrosion resistant in the marine environment due to the formation of a tough aluminum oxide. Aluminum alloys are subject to crevice corrosion, since they depend on the presence of oxygen to repair themselves. What this means is that wherever aluminum is in contact with anything, even another piece of aluminum or zinc, it must be painted with an adhesive waterproof paint such as epoxy, or it must be protected with a waterproof adhesive bedding, or both. A plastic wafer alone as an isolator is not enough. Salt water must be prevented from entering the crevice; otherwise corrosion will result. Anodizing, a process of electrically causing the formation of a tough oxide film on the surface of aluminum, slows pitting, but anodizing will not prevent pitting or crevice corrosion. Aluminum is very active galvanically and will sacrifice itself to any other metal it contacts either directly or indirectly. Aluminum is anodic to everything except zinc and magnesium, and must be electrically isolated from other metals. In this case, paint, bedding, and a non-conductive plastic or rubber isolator should all be used together. Unlike tankers, small metal boats are not designed with an appreciable corrosion allowance. In terms of the paint system, aluminum boats are dealt with more easily than steel boats. Aluminum must be painted wherever things are mounted to the aluminum surface, and below the waterline if left in the water year-round. Otherwise, marine aluminum alloys do not require painting at all. Present technology for protecting metal boats is plain and simple: epoxy paint. Once the metal is protected with a 12- to 16-mil dry-film thickness of epoxy, it can then be top coated with whatever is appropriate to the situation. The top coats can be, for example, foam, enamel, linear polyurethane, or bottom paint. More durable top-coats better protect the investment in epoxy. To assure that this "secondary system" sticks to the epoxy barrier, use a standard extended-recoat-time epoxy primer, which makes an excellent tie-coat. For anti-fouling paint, the excellent offerings from the E-Paint Company should be of interest to metal-boat owners. Called "No-Foul," these paints release hydrogen peroxide to prevent marine growth, eliminating the inherent problems that accompany copper-based paints on aluminum hulls. Whether on steel or on aluminum surfaces, paint preparation is critical. Thorough cleaning and sandblasting provide the best surface for adhesion of paint or bedding. Alternately for aluminum, cleaning and then grinding with a coarse 16-grit disk will provide enough tooth for the paint to stay put. If the surface finish must be extra fine, as on an aluminum spar, then a thorough sanding, cleaning and etching with a product like Alodine before painting will give good results. The interior of an aluminum boat does not require painting. It would be the ultimate, though, to epoxy prime the interior if a blown-in urethane foam will be used. A chromated vinyl-acid "wash primer" would be a very acceptable second choice inside, in order to provide the best surface for adhesion for the foam. Regardless of the bottom paint used, zincs must be used to control stray-current corrosion, to which we can become victim with a metal boat, even without an electrical system! With a scratch at the bow, and another at the stern, the boat itself becomes the preferred path for any ambient currents in the water. In the best of all possible worlds, there would be no stray currents in our harbors, but that is not reality. Zinc anodes should always be used on an aluminum boat, and generally in the same quantities as with a steel boat, in order to prevent stray-current corrosion. The quantity and placement of zincs are discovered by experiment over time, and will differ from one marina to the next. As an example, on a 40-foot metal hull, the best scheme is to start with two zincs forward, two aft, and one on each side of the rudder. With a larger boat, say over 45 feet, an additional pair of zincs amidships would be appropriate. Surface area, not zinc volume, is the important factor. After the first few months, inspect the zincs. If they appear active but plenty of material remains, the zincs are doing their job. If they are seriously wasted, the area as well as the weight of zinc should be increased. Of course, welding zincs on is best, but for an aluminum boat, the zincs will instead usually be bolted to studs welded onto the hull plate, or bolted using stainless bolts into a heavy bolting plate welded to the hull. Good electrical connection between the zinc and the hull is imperative. The Bottom LineCan aluminum compete with fiberglass as a production hull material? Jimmy Cornell's Ocean Cruising Survey, a valuable indicator of trends among world-voyaging cruisers, shows that metal boats are on the increase. A metal hull was the number-one wish of those with other hull materials. "My next boat will be metal..." was heard over and over, particularly by those who were already cruising aboard a metal boat. It is said among dedicated blue water cruisers in the South Pacific, "50% of the boats are metal; the rest of them are from the United States...." Although it may seem so at times, this statement is fortunately not 100% true!! In terms of cost, we usually observe that displacement is more important than length. Aluminum is the ideal material for building a lightweight boat. The second cost determinant is complexity. This reaches into all aspects of the design, including hull shape. The simpler the design, the lower the cost. For example, a well-designed single-chine hull will perform extremely well, and the savings will allow a slightly longer boat. Dollar for dollar, this translates into a *real* performance advantage.With correctly applied protective coatings where needed, adequate zincs, a proper electrical system, and good care over time, an aluminum boat will last indefinitely. Further Considerations...?We believe in metal as the ultimate boat structure, and as a result we have created quite a number of metal boat designs. To review them, please see our Sail Boats Gallery and our Power Boats Gallery. We have also created quite a number of Prototype Designs, most of which are also intended for metal structure. Sail or power - mono or multi-hull - if the structure is well-designed and well built, the resulting boat will be excellent. We are often asked about one metal vs. another - most commonly steel vs. aluminum. Despite the excellent case we have made for aluminum above, we do not have a distinct preference. There are so many varying factors that will contribute to making that decision for each boat, and for each owner. Some boats are designed for one material only, other boats can make use of either. In general, any of our designs that have been developed for steel can very quickly be re-specified for construction in aluminum. The design conversion from steel to aluminum is done for a minimal extra cost. Where NC cutting files exist for a steel boat, they will need to be re-done in order to work for aluminum structure, and there will be a cost incurred for that conversion. Designs originally developed for aluminum structure are not as readily converted, since they will have been designed specifically to save weight. To convert an aluminum design to steel will ordinarily require a re-work of the hull shape in order to support the extra weight of steel. If a conversion of one of our designs from steel to aluminum or vice versa is of interest, please inquire.For more information on the question of hull materials, please see our web articles on the following:Metal Boats for Blue Water | Aluminum for Boats | Aluminum vs. Steel | Steel Boats | Composites for Boats | The Evolution of a Wooden Sailing TypeCopyright 1997 - 2009 Michael Kasten

Direct Quote from an aluminum boat owner... As an owner since 5 years of an aluminum boat I could not agree more with your preference for this material. She is a great sailboat and requires very little in the way of maintenance. I do a lot more reef snorkeling than the paint, polish, varnish and wax guys! --Peter KminekPlease see the Plans List page to review our available Boat Plans.

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Frames First... or Plates First...?A Discussion of Metal Boat Building MethodsThere are a number of approaches one can take when fabricating a new metal boat. Among them are methods that erect the framing first and apply the plating to that structure afterward, and others that favor pre-planning the plate shapes in order to create the hull shape before the frames are introduced inside. The following is a discussion of the various approaches taken, their rationale and the pros and cons of each.With extreme luck, the following will be taken as intended - purely for information's sake. I hope also it will shed light on what has in the amateur metal boat building world become at times a heated debate. You can review our approach to the various metal boat building methods in our article on Aluminum for Boats where they are discussed in detail, including the various pros and cons of each approach toward fabricating. In that article and among the links provided there you'll also find our thoughts on boat shape itself: single vs. multi-chine vs. radius chine vs. rounded hull, etc. Rather than to discuss the merits of different hull shapes here, we will limit ourselves to the question of Build Methods. In this article I will divide the various metal boat building approaches into two broad categories of BUILD METHODS, and then I will address a few basic notions regarding STRUCTURE.The main thing I hope to accomplish here is to attempt to define and to therefore help the reader to understand the various different terms being used when discussing different boatbuilding methods.Here are several thoughts that I hope may help clarify the picture...Structure First, in terms of STRUCTURE, we have in recent years encountered several proponents of so-called "frameless" construction. Unfortunately, when the word "frameless" is used it is commonly mis-construed to imply that a vessel can do entirely without internal structure. Regardless of the various approaches taken toward fabricating and plate development for boats, there will always be a requirement for hull plate reinforcements, whether they occur in the form of floors, longitudinal stringers, bulkheads, web frames, mast steps, engine girders, tank faces, deck beams, or whatever. These are all various types of internal reinforcements, any of which will legitimately qualify for the term "framing." The very notion of "frameless" metal boat construction is by definition therefore a flawed and incorrect concept insofar as it refers to the possibility of a completed vessel being able to exist entirely without frames or other internal metal structure.While it is certainly possible to increase plate thickness in order to increase frame spacing and to therefore reduce the number of frames, it is not at all desirable to eliminate frames altogether. Even with aluminum, the thickness of plate required to completely eliminate frames would end up weighing far too much (and would cost too much) to be practical. Our approach to the so-called "frameless" metal boat construction methods are addressed thoroughly within our article on Aluminum for Boats, in our article on Metal Boats for Blue Water and below under the heading, The Question of Pedigree...Build MethodsIn terms of BUILD METHODS, we observe the following broad categories:1. "Framing First" with the plating being patterned and applied to the already erected frame, and 2. "Plating First" with the frames patterned to the already erected and welded plating - often making use of temporary moulds to help guide the plate and maintain the intended hull shape.This latter method is often incorrectly referred to as being "frameless" because the plating occurs prior to the frames being introduced. This is most unfortunate terminology, is inaccurate and therefore misleading, and is all too often cause for misunderstanding and unnecessary argument.The "Frame First" MethodWith the Frame-First method, the hull shape is controlled by first having a rigid "armature" over which the plating is applied, in other words: the frames. The primary advantage of this method is that it allows exact control over the shape. As a result it is by far the most common approach to metal boat building, whether being used for ships (nearly 100% used) or for yachts (possibly 90% used if Europe is included). We'll limit our discussion to small yachts here (boats under around 60 feet), so we need not involve methods used for larger vessels such as modular construction. In order to achieve a fair exterior hull surface, the "frame-first" method requires that the builder be skilled in the lofting, the set-up of the frames, the patterning of the plate, and the final weld-up of the hull. It is of course exacting work to achieve this level of precision and fairness in the completed hull, but the attention to detail is well worth it in the end..The question then becomes, "How shall we save the builder time...?"With the "frame-first" method, quite a lot of the builder's fabricating time can be saved by having all the frames and plating pre-planned by CAD and pre-cut by NC Cutting via plasma or water jet. What is NC...? It literally means "Numerically Controlled." The high level of precision offered by NC Cutting takes the traditional "frame-first" method to the next level... When using pre-cut metal parts, there is no lofting needed, and there is no cutting required for the frames or plates or other key structures. NC Cutting therefore provides substantial efficiencies to the builder, thus considerable time savings, in addition to offering a degree of accuracy that is simply unachievable by manual lofting and cutting.While NC Cutting can effect substantial labor savings in the hands of a professional builder, it has the potential to save even more time in the hands of an amateur builder. Why? Mainly this is due to the elimination of quite number of "What do I do now?" questions, and the relatively huge amount of time expended on them - inevitable for a first time builder when having to loft, plan, spile, and cut every part of the structure.Needless to say, the NC approach requires a high degree of skill and actual building experience on the part of the vessel's designer in order to be able to pattern all the frames, plates, and other parts correctly. It also requires a high degree of accuracy on the part of the builder who must then place everything as intended, i.e. exactly where it belongs. Ordinarily when using NC Cutting, aside from just the frame shapes being pre-defined, the frames will also have mouse holes for weld-throughs, and will have notches pre-cut to receive the longitudinal stringers. Additionally, there will be all the other parts such as the engine girders, tank faces and lids, stem and horn piece shapes, mast steps, deck beams, bulkheads, and of course all the exterior plating - all of it pre-cut to an accurate fit-up.The result of these efforts is that since all parts are machine-cut to an exacting shape, and the hull can be erected with precision, the builder - amateur or otherwise - can avoid the distortion problems associated with poor fit-up of plates.For further information about the NC Cutting process and how NC Cut Files are developed, we have posted a number of NC cutting articles online. The "Plate First" MethodWith the "Plating-First" method, the plate outlines are precisely defined. They are either developed manually, or from a 3D physical scale model, or they are defined using a 3D CAD model. Then the plates are cut to their perimeter outline, and arranged so they can be pulled into place one by one and tacked together, and finally the plates are welded up. This much can sometimes be done without using internal or external moulds as a guide, but more commonly moulds of some sort will be used. The moulds can be frame segments or they can be other types of temporary guides to the shape. After the hull plate seams are welded up, the frames are patterned to the interior of the hull plating, then the frames are installed and welded in place.The primary advantage of placing the frames afterward is to allow the plating to be welded up first without there being any potential distortion introduced by the presence of a relatively un-yielding frame inside. This can produce an extremely fair hull, and can do so even without there being much skill involved on the part of the builder, thus although it has enormous appeal to amateur or back-yard builders, it also has substantial appeal to many professional boat builders. It is for example the most common method in use throughout the Netherlands, where there is a very highly developed metal boat building industry.The main disadvantages of the "plate first" approach are: That unless the plating is patterned very accurately there can be unpredicted variations in the shape of the hull, there being no internal frame to control the overall shape, nor to provide an indication that the hull shape may be turning out differently than intended; and That the actual shape of the hull must conform to what is a readily developable plate shape, limiting the design somewhat. This "hull shape" restriction is the only significant drawback to the "plate-first" method. It just means that the designer must use fully "developable" hull forms. Though this limits what is possible aesthetically and in terms of being able to optimize the underwater hull form, it is fortunately not a crippling limitation...!When we are discussing any of the various "plate-first" methods, it should be recognized that this approach is really only applicable to the hull bottom and side plating, possibly including the transom. This method however is generally not applicable to appendages such as the keel or rudder, nor ordinarily to the deck and house structures. Therefore, really only about 35% to 50% of the vessel's total plating surface is even under consideration when referring to any of the plate first methods.Just as with the "frame first" method, in order to address the issue of accuracy, the "plating first" method can take excellent advantage of CAD for patterning and NC cutting. This approach will yield an extremely precise plate definition and consequent cutout, and therefore will provide a much more accurate as-welded hull shape. By using NC cutting, the frames too can be pre-planned and pre-cut, making allowances at their joins for the inevitable small variations introduced by the weld shrinkage during the weld-up of the plating prior to the frames being put in place.It should be mentioned that even when using the "plate-first" approach, it may be advantageous to attach a number of internal frame members to the plating prior to it being offered up to the boat, in particular this will often apply to the longitudinal stringers. This kind of "plate-first" approach is rather common among professional builders in the Netherlands. Often, frames are placed as there are opportunities to do so in order to retain the overall shape. For example, once the bottom plating and longitudinal stringers are in place and welded to the keel sides, internal bottom frames can be introduced while the structure is easily accessed, then the topside plating attached and welded up prior to introduction of the side frames. This results in an extremely fair hull, as well as a highly accurate shape.In my view, this hybrid strategy has the most to offer, especially when used with NC cutting. In order for the designer to plan the shape and the NC cutting so that construction can proceed smoothly, it must be determined in advance just what sequence the builder will use to assemble the plates and frames. Variations on a Theme...Within the "plate-first" approach, there are two main divisions: 1. The "Pre-Cut-Plate" method as described above, and2. The "Folded-Plate" or so-called Origami method.With the "Pre-Cut-Plate" approach, the plating is all planned for developability (curvature in one direction only, i.e. not saddle shaped or dome shaped). Here, the plating is all pre-cut, pulled into place - ordinarily over a mould or temporary supports - then stitched together along the seams. This is essentially the "plate-first" method described above.Taking this pre-cut-plate approach one step farther, we have the "Folded Plate" or Origami method, whereby as many of the hull plate weld seams as possible are eliminated via an ingenious layout of the seams and a shape that allows there to be a number of "pre-joined" areas. The advantage of the "Folded Plate" method is that with an accurately pre-planned outline that's cut out of plate, the entire hull plating can first be laid out flat - port and starboard - welded where necessary to create the sizes and shapes required, then it's all pulled together and stitched into place. Using this method, once the plate shapes have been determined, the hull plating can be erected in a very short time - often in a matter of days. Of course this looks impressive...! It actually is impressive! Naturally this concept has captured the imagination of the amateur metal boat building community, thus a possibly significant contingent among potential owner-builders.With the Folded Plate / Origami method however, one must realize that the designer is unfortunately extremely limited in terms of the possible hull shapes that will actually do this trick. Try it with paper cutouts and you will be immediately convinced. You can achieve a few minor variations and still get shapes that will fold together, but regional subtleties of hull form are just not possible. If a different type of hull form is desired, then quite a lot of trial and error time must be spent - usually by making actual trial cutouts and seeing if they will fit together in an attempt to discover a totally flat plate layout that will provide the intended shape when folded together. This is not only a severe limitation on the designer - it also restricts the builder who may as a result have only one basic model to offer. In other words, variations to the hull shape are difficult and time consuming to create, so the vessels are limited to being either larger or smaller, fatter or more slender, taller or shorter, having more or less sheer, yet essentially the same in their general shape and appearance.Further, it must be kept in mind that just as with the "pre-cut-plate" method, the "Folded-Plate" or Origami method is generally only applicable to the hull plating itself, and not to the keel, rudder, deck, or superstructure.We observe then the following disadvantages of the "Origami" method:1. Only a limited portion of the total plate surface will be addressed by the Origami method;2. The variety of hull shapes that are possible both aesthetically and functionally are quite limited;3. There will be quite a lot of fussing around with trial shapes prior to achieving the desired result. As a result of these factors, I have not so-far been tempted to pursue the Origami approach in my design work.Except for the initial "wow" factor, which holds a certain well deserved appeal among amateur boat builders, I don't see much advantage to it, especially in a professional boat building context. In particular, this is so due to the extreme restriction on the variety of possible hull shapes that can be offered. The hull shapes become extremely alike, therefore ordinary and uninteresting. Ask any of the proponents of the Origami method how many truly "different" hull shapes they have been able to design or build using that approach (hulls which are not simply stretched or squished versions of the same thing), and I believe you'll immediately see what I mean.One can just as easily make use of the "pre-cut-plate" approach, and have considerably more freedom with subtleties of hull form.Strategy...?If one is able to begin with a blank sheet, in other words if one is able to create a new custom yacht design, it becomes possible to choose between a frame-first vs. a plate-first building method. In this case, the first task in the design cycle belongs to the owner, and that is to find a designer who can bring about the owner's vision and purpose for the vessel they have in mind.The designer's role is to act as the owner's advocate throughout the whole process, attempting to meld their requirements / requests with what is practical / achievable / safe / etc., at the same time as attempting to achieve the aesthetic, the layout, and the performance being sought. Then once the vessel has been designed, to follow through during the construction of the vessel, first to connect the owner with a builder who is suited to the task, and then to follow through during construction to assure that what has been designed gets built as planned.Occasionally this order of events gets turned around, and the owner first finds a suitable builder, then together they forage for a design that the owner likes and that the builder wants to build. While this can often result in great success, it can also result in great compromise. However if the compromise is not too great, and the cost is attractive, then a deal may be struck that is satisfying to all involved. More often than not though the builder or the owner will want to introduce changes to the design. Subtle variations to the interior, usually introduced by the owner, are to be expected and are usually not of any consequence. Major changes to the layout that involve changes to the structure, or that involve relocating tanks, bulkheads, engines, major machinery, masts, etc. are very often sought. However, any of these kinds of changes must necessarily involve the designer.What is not often realized is that collectively, these changes can quickly eliminate any possible advantage to having selected a stock design. At this point, it can become advantageous to begin from a blank sheet - even if it is largely based on a prior design. Thus, our nearly 100% focus on new custom yacht design.If a stock design is entirely suitable as is, or if minor changes are all that's needed, then certainly the designer will be able to "customize" that design to suit - it is all part of a designer's usual routine.The Question of Pedigree... All the building methods mentioned above can be made to satisfy the structural requirements of the ABS or other rules - with the exception of the so-called "frameless" building method, which cannot. In considering any existing design, one should inquire as to whether the structure has been designed according to the standards of one or more of the yacht classification societies.For motor vessels, we calculate structure per the requirements of the ABS Rule for Motor Pleasure Yachts, or for sail boats, the ABS Rule for Ocean Racing Yachts, or both, taking the most conservative result from each, then adding our own factor of safety. We also consult applicable portions of the German Lloyd's rule and other classification society rules such as Lloyd's Register wherever they may be appropriate, such as for spars and rigging or for wooden structures, etc.Aside from the structure, when inquiring about any stock design or new custom design it will be prudent to inquire about the stability compliance of the vessel being considered. For example, we impose the EU Recreational Craft Directive stability requirements on our designs - both sail and power. Even though there are legally no stability standards imposed on pleasure craft built and registered in the US, we feel this is quite important, therefore the EU-RCD is our base-line standard.You can read about our rationale for use of these standards, what they mean, and how they apply by reviewing our various articles related to "Boat Design" on the Articles web page. In terms of safety equipment, while we very much advocate the use of the ABYC guidelines for safety and systems, there are a few specific areas where we disagree with the ABYC recommendations. Mainly this is limited to those chapters where the ABYC guidelines are at present inadequately developed and are rapidly changing - in particular with regard to bonding and electrical isolation on metal vessels. We address these matters thoroughly in our Vessel Specification which accompanies each design, often amounting to well over 50 pages.ConclusionsA number of our designs are fully developable, and are thus directly adaptable to the "pre-cut plate-first" approach, in particular if NC cutting were to be employed. Examples that come to mind are the 36' ketch Grace and her larger sisters: the 42' schooner Highland Lass and the 42' ketch Zephyr, which have fully developable hulls. Many of our other designs, while largely developable, have intentionally violated developability locally in order to achieve the right aesthetic shape or the right distribution of displacement or the right waterlines or buttock lines, etc. Examples include the 44' schooner Redpath or those designs for which a rounded hull form was preferred such as the 36' cutter Fantom, the 40' schooner Benrogin, or the 50' schooner Lucille.Although we have no particular interest in pursuing the "origami" approach as such, we do believe there to be considerable merit to the "pre-cut-plate-first" approach. More particularly we have observed big advantages to the hybrid "plates-first-then-frame-as-you-go" approach mentioned above. Even though hull shapes are thus limited to only what is developable, there are innumerable good shapes that one can achieve which are aesthetically pleasing and that have a water-friendly shape.To be a success, the pre-cut plate shapes must be precisely planned and cut, but this is not at all difficult when combined with CAD driven NC cutting. We have developed NC cutting files for a number of our designs, and we're continually involved in the development of new designs - and of NC files to ease their construction.Further Considerations...?We believe in metal as the ultimate boat structure, and as a result we have created quite a number of metal boat designs. To review them, please see our Sail Boats Gallery and our Power Boats Gallery. We have also created quite a number of Prototype Designs, most of which are also intended for metal structure. Sail or power - mono or multi-hull - if the structure is well-designed and well built, the resulting boat will be excellent. We are often asked about one metal vs. another - most commonly steel vs. aluminum. We do not have a distinct preference. There are so many varying factors that will contribute to making that decision for each boat, and for each owner. Some boats are designed for one material only, other boats can make use of either. In general, any of our designs that have been developed for steel can very quickly be re-specified for construction in aluminum. The design conversion from steel to aluminum is done at no extra cost. Where NC cutting files exist for a steel boat, they will need to be re-done in order to work for aluminum structure, and there will be a cost incurred for that conversion. If that's of interest, please inquire.Designs that were originally developed for aluminum structure are not as readily converted, since they will have been designed specifically to save weight. To convert one of them to steel structure will ordinarily require a re-work of the hull shape in order to support the extra weight of steel. For some boats, that is not much trouble. For other boats, in particular small ones, steel may not even be an option. If a conversion to steel is of interest for one of our aluminum designs, please inquire. for more information.You will find more information about costs and other considerations between these metals among the essays linked from our Articles web page, and especially in the two articles listed below. For more information about any of the above, please feel free to contact me.Related ArticlesMetal Boats for Blue Water | Strength of Aluminum vs SteelPlease see the Plans List page to review our available Boat Plans.

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Boat Materials

Aluminum. We use only the finest materials available. The 5000 series marine grade aluminum alloy is specifically made for full-time saltwater applications. ALCOA, Aluminum Company of America, put a plate of this aluminum in Narragansett Bay, RI for thirty years and took it out because nothing was happening. We have chosen the 5086 alloy for the whole hull. This aluminum alloy is the absolute best available and thick to boot. With either 3/16 or 1/4 construction, these boats are 2-3 times as thick as most aluminum boats you may be familiar with. If youve ever seen a U.S. Coast Guard 47 footer than youve seen 5000 series aluminum alloy at work afloat.

Gunwale. This 2 3/4 oval in cross-section extrusion gives the edge of your boat incredible durability. Weve had demo rides where a prospective customer inadvertently slammed the boat into cement pilings with just a slight rub to show for it. The only reason to own fenders is to protect the other guys boat.

Chine. Along the length of the chine is an extrusion that both the side and the bottom plates fit into. This high impact area is then double welded the length of the boat. This level of quality is unheard of even in custom aluminum boats.

Non-Skid. This material is applied to the self bailing deck and consists of a polyurethane base and topcoat surrounding an aggressive non-skid abrasive. Not for the faint of heart, nor the bare of foot, this material is similar to the new bedliner material you may be familiar with as an aftermarket application in pick-up trucks. It gives you tough, durable, surefooted-ness in all weather conditions.

Foam. We inject closed cell foam beneath the self-bailing deck into all voids below decks (except around the fuel tank). This high-end system assures you of both unsinkability and upright flotation should you ever swamp the boat.

In short, no expense is spared in making for you the finest boat available anywhere. These materials, used for the first time in a production model boat, truly represent the first in a whole new category of boats.

Black Lab Marine Partners, LLC

207-400-7404

Aluminium Alloys Used in the Marine IndustryAluminium alloys commonly used in the marine industry include: Aluminium-magnesium alloys - 5000 series, used primarily for rolled materials (sheet/plate). Most common are 5083 & 5383. Aluminium-magnesium-silicon alloys - 6000 series, used primarily for extruded sections. Most common are 6082, 6061, 6005A & 6060.

Source: Capral AluminiumFor more information on this source please visit Capral Aluminium.

Aluminum Distributing Inc 5086-H111, 5086-H116, 5083-H116 aluminum for marine use/ sheetwww.adimetal.com/ Marine GradeAlloy Aluminum 5083 5086Structural Marine GradeAlloy Aluminum 6061

Sheet and Plate (5086-H116 or 5083-H116 or Dual)

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Aluminum 6061Chemistry Data : Aluminum : Balance Chromium : 0.04 - 0.35 Copper : 0.15 - 0.4 Iron : 0 - 0.7 Magnesium : 0.8 - 1.2 Manganese : 0.15 max Other : 0.15 max Remainder Each : 0.05 max Silicon : 0.4 - 0.8 Titanium : 0.15 max Zinc : 0.25 maxAluminum 5086Chemistry Data:Aluminum: BalanceChromium: 0.050.25Copper: 0.1 max.Iron: 0.4 max.Magnesium: 44.9Manganese: 0.41Remainder Each: 0.05 max.Remainder Total: 0.15 max.Silicon: 0.4 max.Titanium: 0.15 max.Zinc: 0.25 max.

largerimage Several sizes dual certified

The following specifications cover Aluminum 5083

QQ A250/6Aluminum 5083Chemistry Data:Aluminum: BalanceChromium: 0.050.25Copper: 0.1 max.Iron: 0.4 max.Magnesium: 44.9Manganese: 0.41Remainder Each: 0.05 max.Remainder Total: 0.15 max.Silicon: 0.4 max.Titanium: 0.15 max.Zinc: 0.25 max.

Mechanical Data :

Aluminum 6061-T6Ultimate Tensile Strength, psi : 45,000Yield Strength, psi : 40,000Brinell Hardness : 95Rockwell Hardness : B60Aluminum 5086Form : Sheet Condition : H116 Temperature : 68Tensile Strength : 42Yield Strength : 30Elongation : 12Aluminum 5083Form : Sheet Condition : H116 Temperature : 68Tensile Strength : 42Yield Strength : 30Elongation : 12

Principal Design FeaturesThis is a non-heat treatable alloy for strengthening. It has very good corrosion resistance, is easily welded and does have good strength.

ApplicationsCommonly used in the manufacture of unfired, welded pressure vessels, marine, auto aircraft cryogenics, drilling rigs, TV towers, transportation equipment, and in missile components.

Aluminum Mill Product Specifications

Available Forms:Sheet and Plate ASTM-B928 , FEDERAL-QQ-A-250/7

5086 Marine Grade Aluminum Alloy

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Angles - 25 Ft (5086-H111)(19)

Pipe (5086-H32) Drawn Seamless(29)

Sheet and Plate (5086-H116 or 5083-H116 or Dual)(35)

Flat Bar (5086-H111)(28)

Round Tube (5086-H32) Drawn Seamless(18)

Round Rod (5086-H111)(16)

The Butt Weld Fittings and Flanges (5086)(7)

Sheet and Plate (5086-H116 or 5083-H116 or Dual)

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largerimage Several sizes dual certified

The following specifications cover Aluminum 5083

QQ A250/6

Chemistry Data:Aluminum: BalanceChromium: 0.050.25Copper: 0.1 max.Iron: 0.4 max.Magnesium: 44.9Manganese: 0.41Remainder Each: 0.05 max.Remainder Total: 0.15 max.Silicon: 0.4 max.Titanium: 0.15 max.Zinc: 0.25 max.

Mechanical Data : Form : Sheet Condition : H116 Temperature : 68Tensile Strength : 42Yield Strength : 30Elongation : 12

Principal Design FeaturesThis is a non-heat treatable alloy for strengthening. It has very good corrosion resistance, is easily welded and does have good strength.

ApplicationsCommonly used in the manufacture of unfired, welded pressure vessels, marine, auto aircraft cryogenics, drilling rigs, TV towers, transportation equipment, and in missile components.

Aluminum Mill Product Specifications

Available Forms:Sheet and Plate ASTM-B928 , FEDERAL-QQ-A-250/7

6061 Structural Marine Grade Alloy Aluminum

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Structural Equal Angle (6061-T6)(17)

Structural Unequal Angle (6061-T6)(4)

Structural Flat Bar (6061-T6511)(46)

Structural "U" Channel (6061-T6)(8)

Structural Beams (6061-T6)(3)

Structural Tee (6061-T6)(2)

Round Tube (6061-T6)(4)

Square Tube (6061-T6)(4)

Pipe (6061-T6)(14)

Round Rod (6061-T6511)(14)

Square Bar (6061-T6511)(6)

Flat Sheet (6061-T6)(5)

Flat Sheet (6061-T6)

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largerimage The following specifications cover Aluminum 6061

6061 Aluminum is, by most any measure, the most commonly used aluminum alloy. It is specified in most any application due to its strength, heat treatability, comparatively easy machining, and weldability. If that were not enough, it is also capable of being anodized, adding a layer of protection for finished parts. The main alloy ingredients of 6061 aluminum are magnesium and silicon.

Physical and Mechanical PropertiesUltimate Tensile Strength, psi : 45,000Yield Strength, psi : 40,000Brinell Hardness : 95Rockwell Hardness : B60

ASTM B209, QQ A-250/11

Chemistry Data : Aluminum : Balance Chromium : 0.04 - 0.35 Copper : 0.15 - 0.4 Iron : 0 - 0.7 Magnesium : 0.8 - 1.2 Manganese : 0.15 max Other : 0.15 max Remainder Each : 0.05 max Silicon : 0.4 - 0.8 Titanium : 0.15 max Zinc : 0.25 max

Principal Design Features Probably the most commonly available, heat treatable aluminum alloy.

Applications Commonly used in the manufacture of heavy-duty structures requiring good corrosion resistance, truck and marine components, railroad cars, furniture, tank fittings, general structural and high pressure applications, wire products, and in pipelines.