Aluminum, Salt Water and Different Alloys

We recently received a email asking about aluminum boats and how it holds up in salt water, because this particular individual was told by a friend aluminum doesn't hold up long term in salt water. 

Well I put together a response to that email and i thought I would share my response to him. 

Here is email original question:

"Hello, I have been looking at your boats and wanted to ask what you think about aluminum hulls and salt water? I been looking to upgrade my alumacraft and talking to a buddy saying the next boat I get I should stay away from aluminum's if I plan to continue to play in the sound. After 8 years my boat has shown some salt water damage. I wanted to get your opinion on why I should stay with aluminum boats. specifically if I choose to go with your boats. thanks "

Here is my response:

"Thanks for contacting us with this inquiry. There is a reason aluminum is such a favorite of the commercial industry and is continuing to be more popular with NW fisherman. It is extremely durable, and strong. Fiberglass cracks, fades, and is hard to repair. With aluminum boats, you just use them and don’t worry about what happens. Now you mention salt water and protection from galvanic corrosion. Just like any piece of metal, aluminum will corrode over time, that is why boats that are left in salt water do need to be bottom painted, this creates a barrier from the salt water. It also helps with growth. The second requirement is having the proper cathodic protection. Typically called Zincs. All metal parts should have Zincs on them, like outboards for example have them. They are sacrificial and protect the boats. We don't use true Zincs anymore but choose to use a specific alloy of aluminum that is designed to better protect aluminum boats. Most engine manufactures use material as well. 

As long as you replace your Zincs on a regular basis and keep the bottom paint on the hull you wont have any issues. I have fished on 40 year old boats in Alaska made from aluminum and they are just as good as the day they were new, if you keep up the maintenance on them. Cant say the same for 40 year old fiberglass boats.

Now there are different types of aluminum and they respond differently in salt water. 5086 alloy is generally considered industry standard for commercial boats. 5052 is used a lot in river jet boats because it is softer and can flex more when they hit river rocks. But it is not as good in salt water and does not have the same overall strength properties of 5086.

Aluminum boats are often referred to as Tin boats because of the thin gauge of aluminum used in their construction. That is generally only with the “cookie cutter” style aluminum boats that are mass produced and for sale at big box stores. They are also made with cheaper alloys of aluminum to help with cost and retail price. Now we only choose to only use 5086, it is one of the most expensive alloy grades but is the best. The Navy requires 5086 alloy below the waterline on all their contracts, if that tells you anything.

I hope this helps explain more on aluminum, boats, and salt water use."