Why is dissimilar metal corrosion not a problem on boats?

[jtrom]

I have heard about replacing rivets and other fasteners with ss screws on aluminum boats....as an aircraft mechanic I was always taught that was a huge no no as the steel will corrode the aluminum...just wondered if anyone had a problem with this

 

[robert graham]

Re: Why is dissimilar metal corrosion not a problem on boats?

I believe that dissimilar metals on boats can definitely be a problem, but a lot depends on if your boat is left in the water all the time or trailered in and out, and if it's fresh or saltwater, tied at a slip/marina with shore power, other boats near by. I'm a trailer in, trailer out guy(no yachts), so the dissimilar metal corrosion has never been an issue at all, and my riveted canoe has some Stainless Steel screws here and there, my all-welded aluminum jon boat has a couple of Stainless Screws holding the transducer on, again no problems. Some larger, more complex boats that sit at dock/slips in saltwater most/all the time use a variety of corrosion control methods like sacrificial anodes on the hulls, etc. Good Luck!

 

[Snobike Mike]

Re: Why is dissimilar metal corrosion not a problem on boats?

The short answer is that it most definately IS a problem. Hence the need for sacrificial anodes.

 

[jtrom]

Re: Why is dissimilar metal corrosion not a problem on boats?

So basically on a smaller boat that is used in fresh water a few ss screws is a non issue.....thanks!

 

[sschefer]

Re: Why is dissimilar metal corrosion not a problem on boats?

Agree wth Mike, it is a problem. 18-8 Stainless is pretty close on the scale and it is the best that there is, (all things considered), for use on aluminum boats. What you have to remember is that 5056-H32 is considered Marine Grade alluminum alloy. The 5000 series Al has Magnesium in it that helps to prevent corrosion. 6061 is acceptable but it is heat tempered and although it is weldable it loses 50% of it's strength in the heat affected zone (haz). It has higher levels of Silicon in it. You'll see riveted boats using 6061 because it is stronger then 5052 or 5056 and you can use relatively thin metal and still produce a fairly strong boat.. That's a huge dollar savings for manufacturers. In either case 18-8 Stainless is your best fastner. If you can't weld or rivet the only other choice is glue and that aint gonna work.