Framing includes the transverse frames, stringers, chine bars, stem, and backbone. For small-to-medium-sized boats, you can make the framing from flat-bar stock. For the deck beams and cabin top beams, it’s preferable to use L-angle or T-bar (flange down) as this provides a suitable cavity for the insulation material and also allows the lining materials to be fastened to the inside or underside of the flange as applicable.

Hull frames may be flat bar or L-angle. Our objections to angle used to be that it was more difficult to keep the rust out of the angle. More recently, however, we recommend that all hulls be built from pre-prime-coated steel and have sprayed-in foam insulation. Where the sprayed-in foam is installed, there’s much less chance of rust forming around the frames. Because of weight considerations alone, we would not recommend angle frames in boats under 30 feet ( 9.14 m). Heavy-displacement boats and larger vessels can carry the extra weight and also will benefit from the extra strength of the angle frames. We have just completed plans for a new Spray Pilot House 40, and in this case I have suggested L-angle or T-bar frames be used throughout. The presence of the flange will assist in the lining and fitting out process. On flat-bar frames, timber strips are screwed to the frames to accept the lining materials.

   As mentioned above, the stringers, stem, and backbone will almost always be fabricated from flat-bar stock. Occasionally, solid round bar is used for the hull chines; there will be more on this subject elsewhere in this text. Web floors (also known as solid floors or gussets at the bottom of the frames) should be cut from plate that is the same thickness as the frames.

BRONZE

Bronze is an alloy of copper, tin, and varying small amounts of other elements. It’s a fine boatbuilding metal and it has been used in marine applications from time immemorial. In Roman times, bronze was a prized alloy and had many uses. The exact combination of metals used to make the bronze alloy will depend on its intended use. Copper is the main ingredient, and tin usually accounts for 5 to 10 percent of the mix. Bronze will often take its name from the third metal in the alloy; for instance, phosphor bronze contains about 5 percent tin and 0.5 percent phosphorus, and it is suitable for use in the marine environment. Alloys of aluminum bronze, or nickel-aluminum bronze, are often used for propellers.

ALUMINIUM OR ALUMINUM

Aluminum has been available for over a century, but it’s only in the past 40 years that it has been widely used for boatbuilding. Pure aluminum is a soft metal and not suitable for most commercial applications, let alone boatbuilding. There are many aluminum alloys for various applications but only a few suitable for marine use.

   Some of the metals alloyed with aluminum are chromium, copper, iron, manganese, magnesium, and zinc. Small amounts of these metals are used to improve the industrially pure aluminum. For marine use, the main addition to pure aluminum is 4 to 5 percent of magnesium.

   Because there’s no universal grading system for aluminum, you should check with your local suppliers for advice. The table shows some type numbers and their recommended usage. We have grouped them into UK and U.S. areas; most of the rest of the world follows one system or the other.

   The 5000 series and, in particular, material with the 5086 designation, is the metal most commonly used for boatbuilding. There are several different numbers in the 5000 series and it’s worth checking with the aluminum manufacturer in your country so you get firsthand advice. Don’t be fobbed off by unscrupulous suppliers or merchants who may try to sell you what they have in stock. The 5000 series has excellent resistance to salt water, is ductile, and retains its high strength when welded. In some cases, you may choose aluminum with one designation for hull plating, another for framing, and still another for decks and superstructure.

   When you’re ready to order your aluminum materials, it’s always recommended that you make one bulk purchase. As with other metals, and indeed all your boatbuilding requirements, it’s always best to buy in bulk. If you can find another builder with similar requirements, then a group order is recommended.

   At the same time as you are ordering your aluminum plate and framing materials, you should order the filler wire for your MIG welder. The most common wire is 5356, which is compatible with most aluminum alloys used in boatbuilding, including 5052, 5086, 6061, and 6063. The 5386 wire can be used to weld these alloys to themselves or to dissimilar alloys. (See notes about spool sizes in Chapter 5, Welding.) It’s most important to keep your welding wire clean and to use the spool as soon as it is opened. Store the wire in a dry area, and discard any dirty or contaminated material.

In this book, we’ll mainly consider welded aluminum, as this covers the method by which most boats are built from this material. There are other building methods, however, including small boats pressed out of a single sheet; these are popular in Australia, where they’re affectionately known as tinnies. Riveted construction is still used to build some smaller aluminum boats. Aluminum boats have also been formed by explosive techniques, but this and other offbeat methods are outside the scope of this book.

    For transverse frames you may choose either flat bar, L-angle bar, T-bar or flat/round-top bar. The latter is sometimes used for longitudinal stringers. For longitudinal framing, stringers, and chine bars (if fitted), we prefer flat bar, but the final choice of scantling sections should be left to the designer of your particular boat.

COPPER NICKEL

Copper, one of the most noble metals, has excellent resistance to corrosion in the atmosphere and in freshwater. When combined with nickel to form copper-nickel, it has superior resistance to saltwater corrosion. These features, coupled with its excellent antifouling properties, make it suitable for building hulls, however its huge cost and difficulty of welding will discourage most of us from seriously considering this material for boatbuilding.

BRASS

Brass, an alloy of copper and zinc, has no place as a structural member on any boat, and should never be used in place of bronze. You may have a few decorative items—lamps and the like—that are made of brass. You will know what they are because you will be continually polishing them to remove the tarnish that quickly forms in the marine environment.

   Brass made of 60 percent copper and 40 percent zinc loses all its surface zinc in saltwater, and is soon reduced to a useless mess. Beware of cheap fittings imported from the Far East. They may be sold as bronze, and look like bronze, but they often aren’t bronze. If in doubt, select only materials from known U.S. manufacturers.

MONEL METAL

The ultimate marine metal is Monel metal. It is very expensive, otherwise it would be more widely used. It’s not used for building complete boats but it’s perfect for fittings where ultimate strength and machinability are required. There are two main alloys, including the regular version that contains 67 percent nickel and 28 percent copper. This alloy is ideal for propeller shafting, where its corrosion resistance and durability are best appreciated. There may be some doubt about the use of Monel shafting in steel boats, however, and it may be better to use 316 stainless for your shafting requirements.

The variant “K” is nonmagnetic and is often used for special purposes. Often, Monel is used as the main propeller shafting on minesweepers. They can afford it. It’s also used to protect compasses on boats and aircraft. When more boats were built of timber, and before the wood/epoxy technique was developed, Monel screws were sometimes used on the finest craft, either to fasten the hull planking or in other important parts of the structure. The alloy contains aluminum and titanium as well as nickel and copper. It’s a great metal, but it’s not important to amateur builders of metal boats.

MAGNESIUM

Freshwater anodes are made from magnesium. It may surprise you to learn that protection from galvanic and other corrosion is necessary in all types of water, including salt-free environments. Anodes of zinc are not as effective as those of magnesium in fresh water. Conversely, if you move your boat from fresh water to salt water for more than two or three weeks, you will need to change to zinc anodes; the magnesium ones will rapidly disappear. Copper-nickel hulls do not require galvanic protection in fresh

ZINC

In its pure form, zinc is used for anodes. In salt water, it’s the ideal material for this use. In fresh water, as mentioned previously, magnesium is better. A small quantity of zinc is present in many metals. Zinc is also used in paint primers, paints, and other coatings.

LEAD

With its dense consistency and very low melting point, lead has many uses for the boat owner. The most obvious use for this material is for the ballast, but don’t be tempted simply to pour molten lead into the keel of your metal boat. Even heavy steel keels can buckle if lead is installed in this manner. (See Ballast and Trimming in Chapter 15.)

TOOLS AND SAFETY EQUIPMENT

Because of today’s emphasis on working safely, you’ll want to consider what tools and equipment you need to build, maintain, or repair your metal boat. One of the best and least expensive safety items is a clean work area. Avoid leaving anything lying about that is not in use or needed in the immediate future. These are the things that can trip you up, slash you, or otherwise cause bodily injury. Working with metal naturally produces hazards of varying degrees, but you can protect yourself by having the correct safety equipment. Under no circumstances sell yourself short in this area.

Protective Clothing

   Always wear a proper industrial safety helmet. You never know when something may fall, or be dropped on your head. Safety goggles are a must. They should have side guards to protect you against flying metal particles when you’re cutting, grinding, or chipping. You’ll need a face shield and the various lenses. Don’t forget your ears; remember that good earmuffs are essential. A respirator is required. Invest in good coveralls or a boiler suit. A leather apron and gloves with cuffs are definite requirements. One of our customers built a steel Roberts 38 in a Florida nudist colony. We often wondered how he dealt with the weld splatter. Wear steel-toed shoes or boots, not sneakers, around your metal boat building project.

   Protective hand cream and an adequate first-aid kit are essential. Have the first-aid kit handy because you can’t anticipate when it may be required in a hurry; its presence may save your life or at least prevent a minor injury developing into a major one. Make sure you have plenty of eyewash on hand. A good-sized fire extinguisher and an industrial vacuum cleaner are other essential items of safety equipment.

   Arc welders are relatively safe pieces of equipment, but potentially lethal alternating-current electricity powers them, so you can’t afford to treat them casually. Your alternating current (AC) supply will be 110 volts, 220 volts, 240 volts, or perhaps a larger three-phase supply. Make no mistake: all these voltages can be lethal.

   Watching the arc with the naked eye is not recommended. Even if you look at the arc for a short period with unprotected eyes, you can get arc eye, which is very uncomfortable and feels like sand around your eyeballs. Assuming that you, as the welder, always use a mask, then it must be the assistant or casual onlooker who will need protection.