stainless bolt use on aluminum boat

[seanymph85]

I will be reinstalling the transducer bracket soon and wondered if I can replace rusty steel bolts with stainless steel. There are also some other screws/bolts in the transom in other areas that are very rusty and I would like to replace them with something that won't rust but will be strong enough for what they are fastening. Attached is a picture to show where the bolts/screws are that I would like to replace with something that won't rust.

 

[Barramundi NQ]

Stainless steel and aluminum are better than straight zinc coated or similar steel bolts. Electrolysis still can occur especially with stray current in aluminum boats. Of course, never ground anything to the hull. I've used stainless steel many times on my tinny for all fixings. S/steel doesn't like to give off its electrons as fast as mild steel, hence its usage throughout the marine industry. Sometimes its good to tap a fine thread and then seal with a marine sikaflex. I have snapped phillips pan head screws into one aluminum transom bracket, that can be a b%#$& to get out. I was trying to drive the screw in to make/ tap a thread with too much force and stainless can be softer than mild steel screws....hope that helps.

 

[undone]

In fresh water there isn't an issue, in salt water you may find some corrosion after a while.

 

[Barramundi NQ]

Yeah sorry, I'm only a saltwater boater. Where I am in Aussie most people dont use their boats in freshwater, saltwater is my default setting

 

[Ned L]

The way this is handled on high quality commercial boats & yachts is to isolate the SS from the Al with non conductive bushings, spacers and washers.

 

[seanymph85]

As far as washers goes: The bolt head would be against the transducer bracket on the outside of transom, so if a washer is used is it still needed on the outside of boat? On the inside of boat there was a lock nut and nut. I am uncertain if stainless nuts come with a nyloc style or not but even so I would assume a nonconductive washer would be used between nut and transom. What would the material for the washer be?

Unless larger holes were drilled than needed for bolt holes to use "spacers/bushings" the bolt threads could still touch aluminum. Hate to drill larger holes if I can avoid it.

This boat is only used in freshwater to answer the above comment in regards to fresh and salt water.

Considering a couple of the above comments on fresh water and stainless vs. zinc bolts it would appear on this older boat used in fresh water that I would be better off with stainless than the zinc bolts that rusted badly.

 

[jigngrub]

I use stainless steel sheet metal screws with a good sealant for transducers on tinnies, no loc nuts or washers... never had one fall off or leak and the stainless doesn't rust.

 

[Ned L]

For freshwater I wouldn't worry about corrosion and special precautions. Just use stainless fastening and don't worry. By the way, nylock nuts don't provide isolation, there is still metal to metal contact between the nut and bolt. To answer your question, if the bracket is plastic there would be no need for a special washer on the outside. In a 'perfect' situation, with a plastic bracket you would need only a bushing (plastic) and a washer (plastic - any type) on the inside under the SS flat washer.

 

[seanymph85]

The nyloc nut was mentioned as if an isolation washer such as nylon/Teflon type was required I would not use a lock washer that might cut into the "washer" and would instead use the nyloc nut in place of a lock washer type of fastener.

So given a consensus on the comments regarding stainless/aluminum and fresh water use I won't worry about the need for isolation of the stainless fastener(s).

As well given experience of others with regards to the stainless and transducer mounting I will follow that lead as well.

Thanks for all of the tips on this!