Screws and material for Aluminum Hull - what type to use?

[mydogmax]

This weekend I plan to attach my transducer for my GPS/Fishfinder and my Smart Tabs (Trim Tabs) to my transom.
I would like to know what screws to use that will not cause electrode corrosion with aluminum. I know they make aluminum screws but can you use other types like brass? What do the professional installers use? I might use small nuts and bolts for the transducer (specially welded on the transom) but will have to use screws for the Trim Tabs.
Also, does anybody know what sealant I need to use to secure/seal the screws into the hull? I bought the 5200 (I think 3M product) sealant at West Marine yesterday.
Thank you

 

[AZSenza]

Re: Screws and material for Aluminum Hull - what type to use?

Stainless will always give the least amount of corrosion. Even Aluminum screws (which wont have much strength by the way) will cause dissimilar metal corrosion due to the differences in alloys. Aluminum boats (Glass too by the way) arent much different than the airplanes I work on. The 5200 will be just fine. Try to avoid using any sealant that smells strongly of vinegar, this causes a breakdown of the aluminum oxide coating and can introduce corrosion. Its ok to use it as long as its fully cured prior to getting it wet (usually 24-36 hrs).

 

[krakatoa]

Re: Screws and material for Aluminum Hull - what type to use?

go galvanized screws...

 

[mydogmax]

Re: Screws and material for Aluminum Hull - what type to use?

AZSensa, thank you for your info. Is that photo taken on the Black Canyon below Hoover Dam?
Thank you for the Info. I thought stainless steel would cause corrosion as well?

 

[mydogmax]

Re: Screws and material for Aluminum Hull - what type to use?

go galvanized screws...

Thanks for the feedback.

 

[CATransplant]

Re: Screws and material for Aluminum Hull - what type to use?

I always use stainless steel fasteners on my aluminum boat, and haven't seen any sign of corrosion. I use 3M 4200 for anything that may have to be undone, like mounting transducers.

For blind applications, I use SS sheet metal screws or self-tapping machine screws if the metal is 1/8" thick or more. You can even buy those with a drill point, and do the whole thing in one pass. I like SS drill-point self-tapping screws a lot.

For situations where I can use a nut, I use screws, nylon-insert self-locking nuts, and flat washers...all Stainless Steel.

 

[AZSenza]

Re: Screws and material for Aluminum Hull - what type to use?

That picture is towards the back of Canyon Lake, outside of Phoenix AZ. There is a nice long sandbar back there to "Party" on. Nice cliff faces to jump off of! We usually see big horn sheep comming down to take a drink of water early in the morning.

 

[Splat]

Re: Screws and material for Aluminum Hull - what type to use?

just my $.02. tend to glue a piece of thick plastic or nylon to the transom with some 5200. Then mount the transducer to that. That way no new holes for the transducer, expecially if I have to replace one with a different model. Just a thought.

Bill

 

[mydogmax]

Re: Screws and material for Aluminum Hull - what type to use?

Good news about the transducer is that my Aluminum Klamath boat has a welded plate at the transom for this purpose. Plastic is a great idea if I didn't have this plate. I just want to know what type of screw will be compatible with the aluminum hull. One that will not cause corrosion. I already noticed that I have some factory installed stainless steel screws on the hull. I guess more won't hurt.

 

[Boatist]

Re: Screws and material for Aluminum Hull - what type to use?

My 1980 21 foot Aluminum Runabout has the trim tabs mounted with Stainless steel bolts with a Stainless Steel washer and nut on the inside.
Bennett Trim Tabs were put on in 1982 and of course the hinge and the tabs them self are also Stainless Steel. I do 50 percent of my boating in salt water on the Pacific Ocean and can not detect any corrosion at all.

As far as mounting your transducer use a Aluminum Block instead of plastic.
My small 200 khz 20 degree transducer is just glued on with Silicone Seal under the Aluminum mounting bracket. No Screws at all. It been there since 1981. I did move it one time when I put on a narrow 8 degree 200 khz transducer. It hit debree and kicked up one time but all I had to do was loosen the mouting bolt and put it back down then tighten the bolt. The 8 degree transducer is 4 times the size of 20 degree one but I did put one screw in it.

If I did it again I would use a aluminum block about 4 or 5 inches Square up to 1/2 inch thick and just use Silicone Seal. The plastic blocks will work but harder to find a glue that sticks well to the plastic. With the Aluminum silicone seal sticks very well and also seperates the two pieces of Aluminum
I would not use 5200. I would use silicone seal like I did or 4200 just incase you want to move sometime.

 

[mydogmax]

Re: Screws and material for Aluminum Hull - what type to use?

It sounds like the 5200 is more permanent and the 4200 is something which will allow me to unscrew easier in the future. Is this correct? Thank you for your input. Rich