Rudders & Stocks
GMT carbon composite rudders and stocks offer a strong, lightweight and durable solution for both racing and cruising yachts which takes weight out of the stern and increases the safety factor of the vessel’s steering system.
For over twenty years, GMT has been building rudders for customers who demand the best. The engineering, materials and construction methods that are used at GMT to build every rudder are unsurpassed. Many American syndicates in the last four America's Cup competitions chose GMT rudders. Our rudders have steered many boats to wins in around the world races. Whether racing or cruising to far off places, you can rely on our rudders to deliver you safely to your destination. Here are some reasons why when you consider safety, strength, shape and weight, a GMT rudder represents your best value.
Our in-house staff of mechanical engineers uses computer programs developed at GMT to design your rudder. All posts, except those for special applications like America's Cup boats, are designed to exceed American Bureau of Shipping standards.
Since there are no published standards for the strength of composites, GMT has done extensive testing on different laminates that we have manufactured. This accurate information on the actual strength of the material allows our engineers to design very strong, light parts that will stand up to the rigors of rough weather.
Carbon rudder posts can be made from many different types of material. We use the best; carbon that has been pre-impregnated with epoxy resin. With this process, our supplier uses sophisticated equipment to coat uni-directional carbon with a very precise amount of resin. Our technicians apply layers of this material to the post tool. When the specified laminate is constructed, the post is cured under pressure in our 250 degree oven. Although the pre-preg process is more costly than the process of mixing resin and carbon in a shop, it is much more controlled. With pre-preg, we can build parts that are uniform throughout. These parts won't fail.
Our rudder blades start with a rigid, closed cell, foam. The foam is highly cross-linked to give it excellent strength and stability. It is a material that has been approved by organizations like American Bureau of Shipping, Lloyd's and Det Norske Veritas. In the lightest rudders, honeycomb core is used. The stability of these core materials means that the precise shape we build into the rudder will be the shape you'll be sailing with for years to come. For the rudder skins, we use uni-directional carbon. This material takes more time to apply than woven carbon cloth, but is much stronger. We also use a layer of woven fiberglass on the outside to improve impact and abrasion resistance.
The airfoil shape of a rudder is critical. The blade must be symmetrical about the vertical center plane. If it is not, the boat will steer differently on port and starboard tack. The finished shape of the rudder must exactly conform to what the architect designed or it will slow the boat down and cause excessive leeway. At GMT we start by drawing the airfoil shapes along the span of the blade using AutoCAD, a computerized drawing system. The blade is then faired along its length by another program using three dimensional spine curve-fitting techniques. All this information is then down loaded into our computer controlled milling machine. The operator can then stand back and watch the CAM machine carve a perfectly shaped blade.
We take extra care to finish our rudders to a high level of smoothness. After coating with a two part epoxy paint, the rudder is wet sanded. This takes time but improves the rudder. If you dry sail the boat, you are ready to go. You can also apply any bottom paint directly over this epoxy surface.
The Bottom Line
Quality and care in materials, engineering and workmanship result in a superior product. Of the hundreds of composite rudders that we have manufactured, over 99% have withstood all the stresses the sea has put them through. Our rudders have steered boats that have won the America's Cup, Maxi Championship, ULDB 70 Championship, IOR 50 Championship Around Alone Race and many more world class events. They have been around the world on long distance cruising boats from 40 to 140 feet.
Whether you are concerned about arriving safely at your destination after an ocean passage or first at the finish line after a day race, a rudder from GMT is clearly the way to go.
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Top photo: Farr 44 rudder (white) compared with 20-foot high rudder for 147-foot sloop Lady B, built by Vitters.
Middle photo: using carbon fiber for both strength and reducing weight in the ends applies to both racing and cruising vessels; shown is the GMT rudder for the 112-foot sail-training vessel Spirit of Bermuda.
Bottom photo: carbon fiber is the only practical solution for high-load high-aspect racing rudders like this one.