Marine Grade Aluminum vs. Marine Grade Steel: Which Is Best?

When purchasing accessories for your boat, there are several materials you can choose from, including marine-grade aluminum and marine-grade stainless steel. But, which option is best? Both metals have pros and cons, including their weight and corrosion resistance, especially in saltwater. 

You might consider using a combination of aluminum and stainless steel, depending on the application. Aluminum is better for some uses, while stainless steel is better for others. Below, we’re taking a closer look at the difference between these materials and how to determine which is right for you and your boat.

Marine Grade Aluminum

Aluminum comes in several grades, but the two you should be using on your boat are 5000 and 6000 series alloys. For items made of sheets or plates, aluminum is usually grade 5052 or 5086, while extrusions include grades 6061 and 6063. Grade 6463 is better, and you'll usually find that this material is used for leaning posts, towers, and tops.

Aluminum that is marine grade is typically used topside because it weighs less than steel. It helps keep the weight down and prevents the boat from capsizing. Additionally, smaller boats are made with more aluminum than larger ships, as they do not need as much strength. Another benefit of aluminum is that it is much less expensive than stainless steel.

Depending on the grade, marine aluminum has different percentages of metals. 5052 is 95.7 to 97.7 percent aluminum and 0.15 to 0.35 percent chromium. It also has 0.1 percent copper, 2.2 to 2.8 percent magnesium, 0.1 percent manganese, 0.25 percent silicon, and 0.1 percent zinc.

Meanwhile, grade 5086 contains less aluminum and more magnesium. The other metals also change, but not by much. 5086 has 93 to 96.3 aluminum and 0.05 to 0.25 percent chromium. It also contains 0.1 percent copper, 3.5 to 4.5 percent magnesium, 0.2 to 0.7 percent manganese, 0.4 percent silicon, and 0.25 percent zinc.

When you move up to the 6000 series, 6061 and 6463 have more aluminum while 6063 has less. 6061 and 6463 also have some iron to help strengthen the aluminum. 6061 also has titanium mixed in. Here’s an overview:

• Grade 6061: 96 to 97.4 percent aluminum, 0.04 to 0.35 percent chromium, 0.15 to 0.4 percent copper, 0.7 percent iron, 0.8 to 1.2 percent magnesium, 0.15 percent manganese, 0.4 to 0.8 percent silicon, 0.15 percent titanium, and 0.25 percent zinc.
• Grade 6063: 87.1 to 91.4 percent aluminum, 0.18 to 0.28 percent chromium, 1.2 to 2 percent copper, 2.1 to 2.9 percent magnesium, 0.3 percent manganese, 0.4 percent silicon, and 5.1 to 6.1 percent zinc.
• Grade 6463: 97.9 to 99.4 percent aluminum, 0.2 percent copper, 0.15 percent iron, 0.45 to 0.9 percent magnesium, 0.05 percent manganese, 0.2 to 0.6 percent silicon, 0.05 percent zinc, and 0.15 percent residuals.

You'll find that T-tops, towers, and hardware are often made from aluminum. However, aluminum is soft, so it scratches and dents easily. Boat hardware is often powder-coated or anodized to help protect it from damage.

Marine-Grade Stainless Steel

Sometimes you'll find the less expensive commodity-grade 304 stainless steel for boating accessories, but you should pass that up for Grade 316 for your accessories. Gemlux uses Grade 316 for all of its products, such as cup holders and rod holders. This type of steel effectively resists corrosion and has more strength, thanks to the nickel and molybdenum mixed in.

Unlike aluminum, stainless steel is not easily scratched or dented, so it's great for seat hardware, deck hardware, anchor rollers, and more. The biggest con for stainless steel is that it’s more expensive – but you won't have to replace it as often due to its durability. The other con for stainless steel is that it’s heavy, so using it on top of your vessel could make it more top-heavy, creating stress and possible fractures in the fiberglass.

Grade 304 stainless steel contains 65 to 71 percent iron, 0.08 percent carbon, 18 to 20 percent chromium, 2 percent manganese, 8 to 12 percent nickel, 0.1 percent nitrogen, 0.045 percent phosphorus, 0.75 percent silicon, and 0.03 percent sulfur.

Meanwhile, grade 316 stainless steel contains 62 to 69 percent iron, 0.08 percent carbon, 16 to 18 percent chromium, 2 percent manganese, 2 to 3 percent molybdenum, 10 to 14 percent nickel, 0.1 percent nitrogen, 0.045 percent phosphorus, 0.75 percent silicon, and 0.03 percent sulfur.

Stainless-steel accessories should have a polished finish. The polishing allows the chromium to react with oxygen to create a chrome-oxide surface layer, which helps increase the resistance to corrosion. It also makes stainless steel easy to polish out.

Using stainless steel for your rod holders, cup holders, hinges, and other hardware might cost a bit more upfront, but you'll replace them less often, so you’ll end up spending less money and time on boat maintenance and more time on the water.

For more information about stainless-steel accessories and the difference between 304 stainless steel and 316 stainless steel, contact Gemlux today.