Ted took a little break from his somewhat regular musings here on Sail Far Live Free to cope with a fall that messed up some of the tendons in his hand, a bout with the flu, and an eightieth birthday. But now that he's back on track (and still cranking out sailboat design work!), I asked him to share his thoughts on the advantages and disadvantages of metal sailboats. In fact, Ted was working on plans for a 45' steel hulled cutter with an aluminum deck for a client in Russia when I contacted him recently. What follows is Ted's response to my request for information about metal sailboats.
The Metal Yacht by Ted Brewer
In the 1960's and early 1970's we rarely saw metal yachts in North American waters. Steel yachts had been built in Holland and Germany for many years and I had imported a few in the late '50s and early '60s. But, with only oil paints to protect them, they required a great deal of maintenance and were susceptible to serious rust problems if not properly kept up. Indeed, I've seen lovely 40 foot steel yachts from that era corroded to junk in 10-12 years. A few custom aluminum yachts were built overseas, as well as in some quality yards in the United States, but aluminum was considered to be only for large and expensive craft; half the weight for twice the price was the popular conception. However, due to advance in the protection of steel hulls and the reduction in cost of aluminum, metal can be the material of choice for both custom-built and amateur built yachts and, today, steel and aluminum craft are commonly seen in almost every harbor.
|Kaiulani 34 showing radius chine hull plated up. This particular boat was built in a barn in |
Canada and eventually sailed from the Far East to Australia on a multi-year voyage.
Each material has its advantages but, in the main, the racing skipper will choose aluminum construction for its combination of lightness and strength. The cruising man, on the other hand, may prefer steel for its greater strength and lower initial cost, or aluminum for its longevity, low maintenance and high resale value. Sailors interested in a metal yacht should know the pros and cons of the materials to make an intelligent choice, whether buying a used boat, building their own or ordering a new custom yacht. Here are a few points to consider:
Weight: The easiest comparison is that aluminum weighs about 168 pounds per cubic foot and steel weighs 490 pounds per cubic foot, almost three times as much. It is not that simple though; the machinery, interior furnishings, hardware, rig, equipment and stores weigh about the same for both steel and aluminum craft so the over all weight advantage of an aluminum yacht is not nearly as great as it might seem; generally on the order of 20-25%. Still, that translates into lighter displacement and/or a higher ballast ratio and both mean added performance.
Strength: Comparing strengths is difficult because aluminum alloys lose strength after welding while steel does not. The following table shows the differences between some typical alloys:
Ultimate Tensile Strength
Alloy Un-welded Welded
Aluminum 5086-H34 44,000 psi 35,000 psi
Aluminum 5456-H321 51,000 psi 42,000 psi
Steel - Grade A 58,000 psi
Steel - Grade AH32 68,000 psi
It is standard practice to increase the scantling of an aluminum part to make up for its lower strength of course but, even so, the aluminum still has a very substantial weight advantage. When you consider that the tensile strength of white oak, perpendicular to the grain, is only 800 psi and that of a typical fiberglass laminate is about 18,000 psi, the strength of metal yachts becomes even more apparent.
Steel also has the advantage of being 60% harder than aluminum and so is more resistant to abrasion in a grounding, for example. It is more malleable also so will stretch further in a collision or a hard grounding on granite before rupturing. Aluminum, in turn, has much greater abrasion resistance than either fiberglass or wood and will stretch a great deal more in a collision as well. In any case, I'm sure our readers would never allow their boats to get into a grounding or collision situation so this factor is not critical!
|Arden 60' steel radius chine 3-masted schooner|
In the stretching category I know of a 60 foot ultra-light aluminum design of mine that had her anchor chain slip the stopper while sailing into the teeth of a 50 knot squall, letting the anchor drop 15 feet or so before it jammed. For close to an hour the boat rose on each big sea and fell onto her heavy Bruce anchor, yet the only damage was a number of 2 inch deep dents in her very light .16" aluminum plating. This is an unusual accident but shows one of metal's major advantages. Sailing aboard a metal yacht can be very comforting when you are out on the deep blue competing for liebensraum with floating cargo containers and logs bigger than telephone poles.
Too, both steel and aluminum yachts are essentially one-piece structures without the annoyance of leaking hull/deck joints, leaking chainplates or other weak points. Cleats and other hardware can be welded in place, or machine screw fastened to pads welded in place, thus avoiding bolt holes through an otherwise watertight deck and roof. I've never cared for teak decks on a metal hull for obvious reasons: those thousands of fastening holes through that solid, watertight deck are simply asking for trouble. There are solutions however, such as a shower-grating type deck fastened to pads welded to the metal sub-deck.
Corrosion: The marine aluminum alloys (5454, 5083 and 5086) used for yachts and commercial vessels are very different from the aluminum in your mast. The marine alloys contain a substantial percentage (3.4%-4.9%) of magnesium, depending on the specific alloy, and are highly resistant to corrosion; they are essentially inert in sea water and, if you don't mind the appearance of a dull grey yacht, they don't need to be painted except for the bottom anti-fouling protection. Alloy 6061-T6, used for spars, is a heat treated alloy that is not corrosion resistant and can pit badly in a marine atmosphere, as many sailors have discovered to their sorrow. It is favored for internal use by many builders due to its stiffness and is used, suitably increased in thickness, for frames, longitudinals, keel, knees, and other parts that will not come into contact with seawater. Quality aluminum yachts are plated with 5000 series alloys on all exterior areas and these alloys are used for any part that touches seawater, i.e. shaft tubes, rudder ports, etc.
Steel, of course, rusts quickly in a salt water atmosphere so a steel yacht needs to be protected both inside and out. The interior is usually painted with coal-tar epoxy while the exterior can be epoxy coated or flame sprayed with zinc or aluminum. In either case the steel must be wheel abraded and pre-primed or sand blasted inside and out to provide a tooth for the paint or flame spray, and this extra labour can offset the higher cost of aluminum to a substantial degree.
Both metals are lower in the galvanic scale than copper, so bronze or copper below the waterline is a no-no. Fiberglass-reinforced nylon sea cocks, 316 stainless steel propeller shafting and rudder stocks are the answer. Copper anti-fouling paint is not recommended on the metal either but a coat of epoxy before the copper is applied seems to solve the problem. In any case, proper zincs should be fitted to eliminate electrolysis and replaced regularly. An aluminum ketch of my design, built over 45 years ago at Richardson's Yard in Meaford, Ontario, was still going strong when I last heard of her, a few years ago due to good maintenance and regular zinc replacement.
|Corten cutter, converted to radius chine, made a multi-year circumnavigation|
Other Advantages: Tanks in metal boats can be built-in and this can increase capacity substantially. Built-in water tanks in steel yachts do need to be epoxy coated inside though so very large access clean outs are mandatory, and they're a good idea in all tanks, of course. There has been some discussion about aluminum water tanks contributing to alzheimer's, but we still cook in aluminum pots so I can't get too excited about it.
Steel is fireproof but I'm not sure how big an advantage that is. A fire at sea in any yacht is a disaster and having a burned-out, hot steel hull floating in mid-ocean doesn't seem to be any great blessing to my way of thinking. Aluminum is non-magnetic and that can be an advantage when you're trying to swing a compass, but special compasses for steel yachts are available, of course.
Emergency repairs are fairly straightforward; not quite as simple as nailing a patch onto a wood hull but certainly as easy as repairing fiberglass. Steel can be welded as strong as new and there are scrap yards all over the world. Aluminum, being softer, can be readily drilled and tapped so a gasketed patch of aluminum or plywood can be fitted in a pinch.
Metal boats can be insulated with sprayed-in foam and some claim that this protects the steel if properly done. The result is certainly a very quiet vessel, easily heated and well suited to living aboard in a colder climes. However the foam will burn in a fire which greatly increases the difficulty of making welded repairs, and the gas it gives off is toxic. My own preference is for a fire retardant, semi-rigid insulation glued in place, and good materials are available on the market now.
Hull Shape: European builders have long been able to form fully developed steel hulls but this is an art not often found in North America. Only chine hulls were built here in the early years except in a few high quality, high cost, boatyards. That lack of round bilge hulls is, perhaps, another reason that metal boats were a long time gaining popularity.
However, in the mid '70s, we came out with the Goderich 35, built in Ontario in steel by Huromic Metal Industries. For that design, I developed the "radius bilge" shape; essentially a single chine vee bottom hull with a very large radius along the chine, ranging from a 2 foot radius at the transom to 4 foot at the bow for the 35. With this form of chine shape the boat turned out quite well. Indeed, she was difficult to distinguish from a fully developed round bilged yacht but was simpler to build and was very well received as a result.
|Alaska 43 - Double chine hull that has crossed from America to Australia|
The ease of construction of this hull form is proven by the fact that small fabricating shops, as well as many amateur craftsmen, have built my radius bilge designs in both steel and aluminum in sizes from 30 to 60 feet. In the late '90s a young couple from Alberta had their new home-built 34 foot sloop shipped to Nanaimo and I was simply delighted to inspect it and see that my brainchild had been so beautifully executed. She was perfectly fair outside and impeccably crafted inside; no professional could have done better!
Of course, other designers are now using the radius bilge hull form and plans are available for a wide variety of yachts, sail and power, in all sizes and types. At the same time, many professional yards have mastered the art of producing fully developed hulls and there are a number of custom builders capable of fine work in steel or aluminum or both. Indeed, it's possible to have an aluminum deck and upperworks fitted to steel hulls if that's your preference. Another choice of a number of my clients has been to have the metalwork and machinery done professionally and them complete the joiner work and outfitting themselves.
In any case, metal boats are now seen on all waters of this continent and more are being built every year. If you are in the market for an aluminum ocean racer, or a husky steel cruiser, there are designers and yards that can make your dreams come true.
Steel Boat Building, Thomas E. Colvin, published by International Marine
Boatbuilding with Steel, Gilberty C. Klingel, published by International Marine