Attaching dissimilar metals to aluminum hull

[Rob406]

Hey guys, I have what may be a stupid question here. I am adding a rotary helm steering kit and also a remote control for an outboard into an older 15' aluminum boat. Both of these units are built on (what looks like) a zinc coated steel mounting plate. What is the correct way to mount these accessories onto bare aluminum to avoid any "galvanic corrosion" troubles. How is it done on boats that come with these accessories. I have tried to educate myself to little avail other than there may be an issue. What is the correct way to install these accessories?

 

[Ned L]

You can use something as simple as a piece of HDPE (cut up milk jug) to isolate the two.

 

[Watermann]

Without it being a wet connection between the 2 surfaces then there shouldn't be a problem but I painted mine to prevent any future rust issues.

 

[Rob406]

Ok well with the rotary helm I laid out a gasket from cork gasket material left over from another project. The "bezel" is mounted using s/s hardware and goes through plywood, which is then sheathed with aluminum. So with the hardware there is still contact but it is minimal. But on the remote control it is a little more difficult. I have it mounted directly to a big piece of u channel with 1" mounting flanges on both ends (a "hi-hat" in the sheet metal community) Because of the design of the remote control there is a large plate of zinc sandwiched directly to the aluminum and there is really no way to "gasket it off" without having direct contact one way or another. Is this or is this not something to worry about? The hull itself is usable but in rough shape (year 1957) and I certainly don't want to contribute to making it any worse. I guess I don't understand the science behind all the "principals" of corrosion. Do I just gasket it off best I can and walk away? Is that how you would find a store bought aluminum hull with forward controls?

 

[Watermann]

As far back as I can remember every boat manufacturer I've seen worked on here as had steel used in the boat. It normally rusts and causes pitting in the aluminum. Starcraft for instance used aluminum blind rivets with steel mandrels and then left the mandrels in the bottom of the boat. Lund boats I've seen with steel fasteners and pitting too. So my advice stands as if the boat is dry on the inside it will take a very long time for primed and painted steel to rust out. If the boat is neglected and left uncovered to be a kiddie pool out in the back yard then it will rust, rot and corrode.