MATERIALS: STEEL
Steel has remained my favorite material for boat and shipbuilding. It is readily available, of consistent quality, and it can be welded, forged and cast. The steel used in boat and shipbuilding is readily welded, and even though the several alloys used may differ in chemical composition are readily welded to each other without fear of one attacking the other. Having said this, there are preferred grades of steel (alloys) which give greater corrosion resistance and strength without an increase in weight. The higher the carbon content, the greater the corrosion rate. Thus one seeks low carbon steel A569 that has a maximum of .10; whereas, merchant quality A36 has a maximum of .25. With the former, there is a loss of yield strength, making it easier to form but must often be increased in thickness to obtain the required strength. A36 is, however, suitable for framing and heavier plates such as those used for stems and keels and also can be used for the shell plating. It would be safe to say that the majority of steel hulls are built from this merchant quality steel or, to use the generic term, mild steel. It is the least expensive, and a hull properly built, painted, and maintained will have a long service life. The alloy that I use and recommend for plating 1/4” and under is known as “Corten” which is the proprietary name used by US Steel Corp. for its High Strength Low Alloy (HSLA) steel. It is designated in the steel handbooks as A242. This steel has a maximum carbon content of .09 and, because of its alloying, has a yield strength of 55,000 psi compared to the A36 yield strength of 36,000 psi, and the price is about twice that of mild steel. This suggests that the plating thickness can be reduced to save weight and cost. Sometimes it can in the heavier structures, but there is a practical lower limit of plate thickness that is readily welded. This minimum is generally conceded to be 11 gauge sheet, which is .1196” thick and weighs 5# per square foot. Because of the ease of welding, most of us would rather weld 10 gauge sheet .1345” thick and weighing 5.63# per square foot, and this is the minimum with which some builders will work. I have built several hulls using 16 gauge .0598” thick weighing 2.5# per square foot. With stick electrodes they were very difficult to build and their life quite short as there was no margin for corrosion. This is another advantage of “Corten” since the resistance to atmospheric corrosion is 4 to 6 times that of carbon steel (mild/merchant). This has led some builders to not paint or sandblast the “Corten” which will then deteriorate just as quickly as unblasted and unpainted mild carbon steel. “Corten,” for use in salt water, must be prepared for painting and painted just as carefully as mild carbon steel. If the protective coating is then damaged, the rate of corrosion will be less than carbon steel. Some of the early carbon steel hulls that I built are approaching 50 years of age with no major repairs required. Others using “Corten” for plating are over 35 years old and are still active, and when they are sold it is not uncommon for them to bring two to three times their original building cost. Gauge plate pickled and oiled is also low carbon, and has the further advantage of no mill scale due to processing.
Preparing to construct in steel need not be a expensive undertaking as the equipment costs for the necessary tools are very modest, i.e., $500 to $800 in the year 2000. Required is a 225 amp AC/DC welding machine for stick electrodes, helmet, gloves, oxygen/acetylene cutting torch, heavy duty grinder, electric drill, 6 C clamps, come-along, wrecking bar, chipping hammer, cold chisel, punch, vise, assorted malls, sledge hammers 4# to 15#, and a 2” to 3”slab of steel 16” x 30” for use as an anvil. If only one hull is to be built, this is all most builders will need. The time needed for construction will be higher than that for a builder that makes a further expenditure, which will ease the physical labor as well lower the cost. The equipment I find beneficial is a plasma arc cutting torch, which is not only faster but causes the least distortion and, when correctly done, eliminates 95% of plate edge grinding. The saving here is in not working a backbreaking arm-tiring 15# grinder and the consumable grinding wheels. An advantage is the ability to cut openings, say, for portholes in the middle of the plate without distortion. The next is a MIG welding machine. This method uses a continuous solid or flux cored wire of small diameter (.035) versus 1/8” stick electrode. Like the stick electrode, the flux cored wire can be used in the open on a windy day and have consistently sound welds. The use of a solid wire requires a shielding gas, which leaves a clean weld that does not need to have slag removed. This is practical when construction is done under cover, since anything more than a light breeze will blow away most if not all of the shielding gas, thus prohibiting sound welds. In some instances, a portable screen can alleviate some of this problem. The lower heat input and speed of metal disposition makes it easier to control distortion, the gun is very small and lightweight, and also there is no stub loss. An auto-darkening shade glass for the welding helmet eliminates the need to lift the helmet to see where to start and where to move.
Of course other things that are useful are quick-acting bar clamps in lieu of C clamps. I have 40 and am only building for my own use. Also helpful are lightweight grinders (4”) in addition to the 15# grinder, one with a grinding wheel, one with a wire brush, and one with a sanding disc, and several 3/8” heavy duty drills with quick acting chucks. The above probably saves me 1/3 of the total hours to construct a hull than IF I had stayed with just the minimum equipment.
For the most part, straight sections are used, and cutting the correct length and mitering the joints of the frame is all that is required to making the frame. Plating is usually straightforward with no compound curves except in the bottom forward portion of the bottom plates. Here the solution is to use narrow strips, usually about 12” wide and 8’ to 10’ in length, and trim them to fit each other. In other words, in metal construction, one need not use a conical section because of material limitations. The framing systems are basically all transverse frames closely spaced, transverse frames approximately double-spaced with longitudinal stringers, and widely spaced transverse webs with closely spaced longitudinal stringers. Transverse frames are either Flat Bars or angles. Angles are the strongest, lightest, and stiffest, and occupy less transverse space. The objection to them so often heard is that they are harder to paint. They can be, but how often in the life of a vessel will they have to be painted again? My personal preference is for only transverse framing on vessels plated with 7 gauge (7.5#) and over. Below this, the use of longitudinals often produces a fairer hull, especially those that are not meticulously lofted. Transverse Web frames are usually T sections and occupy more space than regular frames. It is well to remember when using longitudinals that they are one of the prime sources for the deterioration of the shell plating from the inside of the hull, so limbers must be carefully located to prevent any water buildup.
Round bottom construction in metal requires a knowledge of stretching metal, which is not difficult to learn. With learning comes experience and, at times, when one is just beginning round bottom construction, it can be frustrating. One edge of a frame can be hammered with closely spaced blows to form the required curve. This is hard work. Heat can also be used via a rosebud tip on the acetylene torch; however, a helper is almost a necessity since, before the torch can be laid aside, the metal has cooled enough to inhibit a true bend. A small forge with open ends allows one to remove the metal quickly and work alone without the need of a helper. Some of the larger boatyards have a furnace, and the whole frame comes out white hot and is quickly bent to a pattern. The small boatyards usually make a hydraulic frame-bending machine. These are of numerous individual designs based on the yard’s need and experience; and they are either horizontal or vertical from 5 to about 150 tons capacity and range from hand operated to machine driven. A 10-ton bender seems to be adequate for vessels up to about 30’; a 20-ton bender for vessels up to about 45'. The frames are usually bent in pairs so that one complete bending operation of a frame will result in a complete port and starboard section. The same holds true for deck beams by bending in pairs which saves time, even though this results in some scrap. A method of obtaining a bent frame that is often used by the inexperienced is to cut the frame out of plate and weld on the flange or just leave it as the equivalent of a flat bar. The edges must be ground smooth and the corners rounded off to hold paint. There is a lot of labor and scrap using this method.
Plating of a round bottom hull requires a plating model on which to lay out the plates so that the builder is assured that they will not only wrap around the hull, but will also fay against each frame. It is of course possible to do this on a trial and error basis directly on the hull, but it will be found that the errors, if significant, result in either a large scrap pile and/or a rough hull. The lesson learned is once is enough--make a model.
MATERIALS: ALUMINUM ALLOYS
Aluminum Alloys are a fine medium for the construction of all types of marine vessels. Being a metal, almost any vessel that can be built in steel can also be built in aluminum alloys. There are a few glaring exceptions such as a Dory, which depends on a heavy bottom for a large portion of her stability. The reverse is not true for vessels designed in aluminum because the lesser weight of aluminum alloys permits a lesser displacement for the same type of steel hull.
In practice, to achieve the same strength as steel, it is mandatory to increase the scantlings approximately 50%, thus 1/8” steel = 3/16” aluminum; framing is also proportionally greater in sectional area. While the theoretical difference in material weight of aluminum is 1/3 that of steel, in actual practice the difference in structural weight as built gives only about a 30% savings over the steel hull. This must not be translated directly as a reduction to displacement as the engine, fuel, water, all other equipment, and joiner work remain virtually the same. I was at one time the Consulting Naval Architect for Kaiser Aluminum Company and can cite hundreds of reasons for and benefits of choosing aluminum alloys. Unfortunately, it is not a trickle-down effect that has much meaning in small vessels. Instead I prefer to think about some of the benefits as well as the demerits of aluminum construction
When welding aluminum, I would place cleanliness at the top of the list. One cannot expect to obtain sound welds using the same procedures that are standard practice in steel construction. Indeed, after working in aluminum and then returning to steel one finds the habit of clean joints so ingrained that it is automatically carried over. Weld rejections become a rarity.
Welding aluminum is very similar to welding steel, EXCEPT in cutting and otherwise preparing a plate or shape for welding using power tools, such as a saw, sanders, routers, and grinders, which can impart enough heat to actually melt some or all of the metal in the joint, causing a heavy scale to form. The scale melts at roughly three times the temperature of the parent metal; therefore, when welding, an undue amount of heat has to be induced, and this slag then precipitates into the weld zone causing inclusions and porosity. Unless carbide blades are used for sawing, a lubricant must be used to prevent the blades from gumming up. This is usually a stick wax rather than a cutting fluid. The solution is simple, and that is to wipe all effective areas with toulol and then, with a hand file, clean up all the edges to be welded. This may sound like a monumental task, but for 20’ of joint about 2 minutes is all that is required, as the thickness of the scale is not much more than .0001” or 1/000” thick. Weld cracking is common when welding aluminum and most often it can be traced to poor preparation and welding sequence. After the plate or shape is ready to be welded, use a hand stainless wire brush to the joint or seam to be welded and then wipe the whole with toluol. Now weld, using standard procedures and techniques. I do not believe in welding from one side only on shell and deck plating as both are subject to flexing and to impact loads. The exception is when it is impossible to make the weld on the closed side, at which time I use ceramic backing strips which are grooved to form the back bead. The strength of a completed aluminum weld is about 80% of the parent metal strength due to the loss of strength in the HAZ (heat affected zone) which is alleviated to a certain extent by careful location of butt joints and seams. When welding from both sides, it is, as in steel, necessary to get back to sound metal in the root of the first pass. This is best done by power gouging, but this is very noisy. Today we have small grinding wheels made for working aluminum that do not gum up and by using light pressure and rapid movement will not melt the aluminum. The same wheel is not suitable for, say, beveling.
Some of the advantages of aluminum are: it is lighter; welding and sanding require less time; requires no paint except for antifouling purposes; does not rust; can be cut with woodworking tools and plasma arc; and it is easier to machine. Also, the scrap has a high value; it is non-magnetic; and longer and wider sheets and plate can be used because of its weight and stiffness. The savings in the cost of paint and sandblasting are quite significant. For example, sandblasting the exterior hull, decks, and cabin trunk of a 40’ steel troller is $1600 to $2000. If the inside is also blasted, add $3000 to $4000. The barrier coats and primer, inside and out, plus the finish color coats cost about $2000. This buys a lot of aluminum. The pilot house of wood used on steel vessels costs more than an aluminum pilot house used on aluminum vessels. Special shapes can be extruded at a nominal cost for dies. Unused portions of a plate that would normally be scrap in steel can be cut into flat bars and pieces for other small fixtures. It is well to remember that in cutting, say, with a Skil saw, there is NO distortion. I have found that 20’ x 8’ plates are quite handy; whereas, in steel, say, 4’ x 14’ or 5’ x 12’ would be my choice in that they must be cut with heat.
There are some detractions of using aluminum in boatbuilding. There is a limited number of suitable alloys for marine use; these are in the 5000 and 6000 series; and the numerous remaining alloys should never be used. Except in rare instances, aluminum should not be heated to make several bends, and cannot be forged to make fittings and other parts. It costs about 6 times more per pound than mild steel, thus extra care must be exercised to derive the most out of each plate to minimize the scrap. Extra care must be exercised to isolate any dissimilar metals from the aluminum and, with the exception of laminated wood cabin tops, wood bonded to aluminum should be avoided due to the probability of poltice corrosion
Materials - Wood
Wood is one material that I enjoy working with and have built many boats of this material. Every boatbuilder must have the basic skills associated with woodworking; however, few achieve the status of master carpenters, yet are capable of very fine joiner work and finishes. In boat and shipyards, construction of mold lofts, building ways, pattern making, and interior joiner work are but a few instances where woodworking skills are required.
I have designed and built lap strake, plywood, carvel planking (double and single), strip planked and Ashcroft hulls, and have used sawn, laminated, and steam bent frames. I have also built composite hulls, which are framed in steel often in conjunction with steel floors, keel, and garboards. Building in wood requires only hand tools, which can be obtained at a reasonable cash outlay. All the needed tools can be carried in a carpenter’s box at one time without getting a hernia. I have built many boats from 8’ to 50’without any power tools. This was because power was not available and if it were I could not afford the power tools. Even after WWII when hand power tool prices were affordable, my yard at that time was powered by old generators that were either broken down or about to break down, so it became a case of are you building boats or are you fixing machinery. When power lines were finally extended to the yard, power tools were not only used but also welcomed. There are individuals today that wish to emulate their forefathers and never use power tools. Believe me, had my great-grandfather had a power saw or an electric drill he would have used them without hesitation. Power tools may not have made him more productive but he certainly would not have been as tired at the end of a day
Speaking of power tools, it is quite easy these days, due to advertising, to become tool poor as the implied notion seems to be that if one has all of the best tools then all work produced on them will be the best, especially if each tool has a dedicated purpose. It is the ability of the craftsman, not the tools, that determine the excellence of a job. Often more time is spent setting up these power tools to do a task than would be expended if one had used hand tools.
The popular notion that plywood is the best and simplest for the owner/builder is not always true. Plywood planking dictates the shape that the vessel must have to permit its use. In V bottom hulls the conical development of the forward bottom produces convex sections that are prone to curling a sea up and onto the deck. This is lessened by the use of spray rails or modifying the chine by inducing a flat area that deflects the sea. In other words, a problem is being cured which need not have existed in the first place had the proper material been selected from the beginning. Plywood planking covers a hull very quickly; however, it can require a rather complex framing system and, when the chines are properly constructed, often requires skills beyond the capabilities of many owner/builders as well as professional builders. Plywood hulls are often glassed and the chine construction simplified in the hope that one will offset the other and will allow mediocre woodwork to pass as good. Short term, it can work, but I have noted many failures in the long term. Many were due to poor workmanship and others due to moisture saturating the chine area and popping the glass. Small craft chines are often made via the quick stitch and glue method, the longevity of which I suppose is predicated on how well the wood is sealed in the surrounding areas. Glassing over a wooden hull to cut the cost of woodworking is the same as saving with a spoon and spending with a shovel. A wooden hull properly constructed and maintained has a very long life without the need of glassing.
For skiffs, flat or V bottom, the cross-planked bottom is by far the least expensive and quickest method of construction. Plywood topsides are often incorporated in smaller hulls. In larger hulls, such as sharpies of 50’ to 60’, the use of thicker topside planks permits the use of edge bolts to strengthen these slender shallow hulls.
In round bottom hulls, constructing with single sawn frames and strip planking is the easiest as well as least expensive method of construction. The frames are the molds so there is little waste material. Steam bent frames require molds; therefore, for multiple buildings, this method is the least expensive as one set of molds suffices for all subsequent hulls. It matters little if the hull is strip or carvel planked as the frame spacing can, if necessary, be adjusted to suit without changing the molds. One advantage of using molds is that hulls can be stretched in spacing or spread at the midship mold to create more cargo space. In strip planked hulls I have found that lining off so that the strips are parallel to the sheer is the most satisfactory method, especially if a heavy wale(s) is to be incorporated as the sheer strake. Carvel planking, even though the planks must be spiled, is straightforward and planks up faster than strips if the strips are hollowed and rounded.
The difficulty today is the general availability of properly sawn wood and obtaining the quantities required for the construction of a vessel. In the past, I have employed a timber broker to search out, purchase, and deliver timbers and planks dressed to my specs to my yard. Today, I fit in the category of a backyard owner/builder, thus I search through lumber piles long before I need it to select the suitable material. This, of course, is time consuming. When selecting planking material at a local lumberyard or builders supply house, one quickly discovers that all are not the same thickness or width as the lumber may come from a dozen different sources. A power planer is then a necessary power tool for the yard, especially if the material required is not a standard dimension. I have been quite happy with the 10” and 12” portable planers. In the past dozen years I have used pressure treated lumber for all framing, planking, decking and exterior woodwork. Unless it is purchased as “dried after treatment,” it must be treated as green wood and stacked and stickered to dry. I find that during our hot season (May to October) 5/4 wood will dry out and become dimensionally stable in 5 months, and 6 to 7 months during the cool of the year. I have a personal dislike working with plywood, but highly recommend it and use it for bulkheads, decks, shelves, berth bottoms, and cabin tops. Using MDO and HDO ply (medium density overlay and high density overlay) on cabin tops, I seldom glass it over since the phenolic overlay is very durable. I am not averse to using canvas rather than glass if the top must be covered.
I attribute the longevity of many of the older wooden vessels to the use of oil based paints during their construction. These paints were formulated by the builder. Using these formulae allowed the paint to be well-thinned and to soak into the wood. Today many use quick drying paints and sealers which are not absorbed into the wood but merely lie on top, entrapping moisture and hastening decay. Wood must breathe.
