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The choice of building material is perhaps the single largest decision affecting the quality, performance, and environmental profile of any yacht. Because of that, this section is comprehensive.
Like a growing community of globe-trotting sailboats, fishing craft, tugs, Coast Guard and military craft and commercial vessels, Trekker yachts are fabricated using the highest quality marine grade aluminum. Properly constructed, aluminum is the world’s premium yacht building material. Due to the proliferation of plastic production boats, few yachtsmen are aware of the many advantages of aluminum. But for custom and semi-custom built vessels ranging in size from a small 30 foot Alaskan salmon skiff to a 200 foot luxury ship for Arab oil sheiks, aluminum is the material of choice. The reasons for Trekker’s use of aluminum are many, as you will learn. Although there are some good applications for fiberglass and steel, the choice of aluminum is a key part of Trekker’s adventure class strategy. A short list of the material benefits of marine grade aluminum over fiberglass and steel is as follows: • Highest strength
to weight ratio Of course, you never hear a fish peddler shouting “rotten fish.” Companies using fiber reinforced plastic will extol the virtues of their material, and steel fabricators will focus on the unique properties of this metal. But be aware of what they don’t say, and how they frequently offer only the “positive” characteristics. At Trekker, we will endeavor to give you all of the data so that you can fully understand and appreciate our commitment to aluminum structures for adventure class construction.
The marine aluminum alloys, identified as 5454, 5083, and 5086 alloys, are quite different from the aluminum used in household products such as pots and pans. These special marine alloys contain no copper and from 3.5 to 4.9 percent magnesium. They are so resistant to corrosion when in sea water that they are considered inert. These 5000 series alloys are also different from the 6061-T6 aluminum that is used in sailboat masts. This material is heat treated and loses 30 percent of its strength in the vicinity of a weld – a quality that we do not care to see in our hulls that contain hundreds of feet of welding. Proper welding of 5000 series marine alloys produces strengths roughly equal to that of the parent metal – ranging from 39,000 to 44,000 pounds per square inch after welding compared to 24,000 PSI for the 6061-T6 material. For the production of adventure class yachts, where the focus is on strength, safety and durability, aluminum easily beats the competition. Let’s have the facts speak for themselves.
Aluminum is significantly stronger per pound than fiberglass or steel. Welded marine aluminum has a tensile strength of at least 39,000 pounds per square inch and weighs 168 pounds per cubic foot – providing a strength / weight ratio of 230. Mild steel has a tensile strength of about 58,000 to 68,000 PSI, but weighs in at a hefty 470 pounds per cubic foot – providing a strength / weight ratio of only 123 to 145. Fiberglass strengths vary widely depending on the type of material, mat, woven roving, or cloth, along with the orientation of the weave, ratio of glass to resin, and quality of workmanship. The American Bureau of Shipping allows an average tensile strength of 18,000 PSI for typical production boat construction laminates which will weigh about 95 to100 pounds per cubic foot – providing a strength / weight ratio of 180 to 189. Aluminum’s superior strength properties mean that for any given specification, aluminum can match other common materials using less weight, or provide much greater strength at a comparable weight. We should note that certain exotic and expensive constructions using Kevlar, carbon fiber, epoxy resins and other state-of-the-art materials can equal or better the strength / weight ratios of all the common materials, but only at a significant increase in cost typically reserved for high-tech racing machines. And their load characteristics are a bit unnerving as they tend to “explode” when their design limitations are exceeded. Perhaps you saw the America’s Cup sailboat snap into two pieces and sink within a few seconds? High tensile strength is one thing; a practical and forgiving material for dependable cruising is yet another. Another important strength characteristic of aluminum is its ability to stretch, allowing for the hull to bend and dent rather than fracture as would fiberglass. Aluminum hulls that have endured tremendous poundings on rocky shores for extended periods without leaking a drop. While a well manufactured fiberglass boat may survive a grounding, they are not up to the punishment of repetitive pounding. Manufacturers of plastic trawlers and expedition yachts often resort to overkill to try and protect the bottoms of their vessels. Some of their web sites show images of incredibly thick cross-sections of their hulls, and now you know why. But the penalty is in the weight of the hull structure – a serious limitation that a naval architect would rather invest in other ways
Aluminum has the considerable advantage of light weight because of its superior strength / weight ratio. The following reference shows the plating thickness normally used on a yacht of about 50 feet LOA and the weight per square foot of the hull skin: • Aluminum @ .1875 inch (3/16) = 2.5
lbs. per square foot Naval architects love lightweight structures. Additional tankage and cargo can be added to any given vessel, and smaller engines / less fuel can be used to move the vessel and increase range – and/or converted into higher hull speeds. Weight saved in the hull, decks, and superstructure can be traded for increased tankage. More fuel, water, and grey/septic fluids can be stored low in the hull – maintaining optimum stability while increasing performance in all areas. Integral Tankage Aluminum is unaffected by diesel fuel and makes excellent fuel, water and holding tanks. Unlike stainless-steel tanks, which can develop pin hole leaks due to crevice corrosion, or black iron tanks that rust from the outside, aluminum tanks last indefinitely. And with an aluminum hull, an additional benefit is the double bottom created by integral aluminum tanks using the hull plating to form one or two sides of the tank. And once again, this leads to additional weight savings – a string of benefits not available to boats with steel or plastic hulls.
Trekker’s standard practice is to finish each yacht with the hull, topsides and superstructure largely unpainted. Instead, the shiny silver surface is massaged to a soft silver patina with an organic blast of ground walnut shells. Aluminum saves significant amounts of time and money by earning its reputation for requiring the least maintenance of all boat materials. Unpainted marine aluminum can be rinsed with fresh water and allowed to dry. No more chamois and towel chores. A mild bio-degradable soap may be used if the surface is dirty, but forget the polishes and waxes. The hull, topsides, and superstructure will darken slightly over time – building a natural protective layer that eliminates corrosion. This soft silver patina is the perfect backdrop to the beautiful array of adventure craft that adorn every Trekker. If you are compelled to polish something, then polish the toys! While the overwhelming majority of yacht builders mesmerize their buyers with gleaming white hulls, Trekker’s dazzle the crowds with a massive dose of rugged functionality. To explore, or to wax. Hmmmmm. Over the lifetime of a yacht, the time and money spent on polishing, waxing and drying of fiberglass, or the constant corrosion battle with steel is easily replaced with the selection of aluminum.
Building adventure class yachts means adapting each vessel to the array of adventure craft chosen by the owner. Nothing can match aluminum’s relative ease and low cost of making structural changes to suit each project. There are no expensive fiberglass molds that limit the shape or size of each detail, and the custom framing for racking the auxiliary craft can be welded directly to the boat’s superstructure. This produces the strongest relationship between the mother ship and her smaller vessels in any sea condition. Safe, secure, and built precisely to the needs of the owner.
A properly built and maintained aluminum structure will be as strong in 100 years as the day it was launched. The material simply does not loose strength. Once completed, an aluminum boat is one piece of metal without glued and bolted deck and superstructure joints. This provides a one-piece “monocoque” structure that does not flex and twist, and is impervious to hot and cold climates. Marine grade aluminum will not absorb water, blister, delaminate or rot. Steel boats are high maintenance structures, and the best techniques only slow down the ablative process. Plastic boats slowly absorb water throughout the gel coat like a sponge and are prone to cancer-like blisters and layer separations that are expensive to repair. And fiberglass must be over-built as it looses up to 30 percent of its strength during normal use and exposure to sun / heat. An aluminum structure can be expected to remain unchanged and last indefinitely. And collisions and groundings with immovable objects that would easily puncture steel or composite hulls often just dent aluminum ones.
Plastic boats burn like torches – all the way to the waterline due to the flammability of the petroleum-based resins. Aluminum, as defined by SOLAS standards, is non-sparking, non-magnetic, non-flammable and non-combustible. For increased peace of mind, there is nothing better than the fire resistance of a metal hull.
Modern marine aluminum is an ideal material to naturally resist damage from the elements at sea. Leaving the yacht largely unpainted can save 10% of the build cost – offsetting aluminum’s higher expense and providing Trekker owners with the most practical and durable platform to experience their adventures.
Well built and maintained aluminum yachts maintain a significantly higher resale value than plastic or steel. Their strength, low maintenance and long life durability have earned the industry’s highest used market valuations.
Steel is less expensive in the short run and easy to weld. Like aluminum, there are no expensive molds to build, making this material appealing for budget-driven one-off boats and commercial hulls. The low material cost has been the highest incentive in the use of this easily corroded metal. Due to its poor strength to weight ratio it is common to use steel for a hull, and then switch to aluminum and fiberglass for the superstructure. But in many demanding applications from passenger ferries to Coast Guard vessels, aluminum is becoming the preferred material. Fiberglass is the cheapest process for constructing acceptable production boats. Once a mold is built, the manufacturer can churn out identical copy after copy. And fiberglass lends itself to smooth curves, important in achieving the glamour look in many motor yacht designs.
Aluminum fabrication is a demanding process that is best conducted by a proven shipyard that utilizes dedicated facilities and personnel to work with aluminum. Additionally, designing and building to meet stringent industry standards such as the American Bureau of Shipping is an important strategy to insure a vessel’s highest integrity. Very briefly, the following are key points to achieving World-class aluminum construction: Certified and tested marine grade aluminum. Premium aluminum yachts begin with premium aluminum. Trekker purchases material only from the best producers, and then independently tests the material to verify its properties before it is placed into the production process. Precision material preparation. The quality of aluminum construction is directly proportional to the careful and accurate preparation of the various plates and support members. Smooth and evenly separated seams produce smooth and evenly penetrated welds. All of Trekker’s materials are precision cut using proven 3D modeling files. Certified aluminum welds. Certified welders working in environmentally controlled facilities are required to produce certified welds. All strategic welds are then easily x-rayed to verify optimum weld compliance. Electrolysis prevention. Because Aluminum is less “noble” than many metals traditionally used on boats, a few extra steps up front assures that aluminum boats uphold their reputation for low maintenance. Aluminum’s one material issue is that it is susceptible to electrolysis if it is in the vicinity of any copper-based metal such as brass, bronze, or copper itself. Proper design, construction and maintenance procedures are well known and simple but must be followed carefully. Examples: sea cocks must use fiber reinforced nylon valving and bottom paints must be formulated for aluminum hulls. If a bronze propeller is used, the hull must be protected with zincs, and the zincs must be monitored for condition. This is simple, but must be adhered to because failure to maintain zinc integrity will then establish the aluminum as the sacrificial anode, and structural corrosion would occur. Electronic gauges are easily installed for automatic remote monitoring. Zinc replacements occur normally during regular bottom cleaning operations.
Trekker’s entire platform is a showcase for the many advantages of aluminum. Our high quality semi-custom yachts effuse toughness, durability and safety, ease of maintenance, fuel efficiency, and an eternal focus on the adventure. And when you are ready to trade your Trekker in for your next one, your used Trekker will fetch a considerable market premium because of the anticipated low maintenance costs and extended longevity of its World-class aluminum construction. The World is changing. Trekkers will lead. |
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