SS screws in alum frame window?

I'm in the middle of installing larger Krogen 48 salon windows in my Manatee 36. After speaking to Krogen about any possible stress risks, I am moving forward on the project but since these windows are stronger, thicker , screw-fastened alum framed instead of the original plastic glue-in jobs, the usual SS screws I use for most things may not be appropriate against the aluminum. Should I look for alum screws or just dab the holes with some Algrip primer or something? Thanks in advance.

healhustler said:

I'm in the middle of installing larger Krogen 48 salon windows in my Manatee 36. After speaking to Krogen about any possible stress risks, I am moving forward on the project but since these windows are stronger, thicker , screw-fastened alum framed instead of the original plastic glue-in jobs, the usual SS screws I use for most things may not be appropriate against the aluminum. Should I look for alum screws or just dab the holes with some Algrip primer or something? Thanks in advance.

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Liberally apply Tef-Gel and use nylon washers.

Stainless steel and aluminum are quite aways apart on the galvanic chart.

I was told of a case where a floatplane owner decided to replace a lot of the galvanized fasteners in the plane's float system with stainless fasteners thinking they would hold up in the saltwater environment he flew in better than the galvanized fasteners which would start to rust as the galvanizing went away.

The result was severe corrosion in the structural aluminum around the stainless fasteners and a serioulsy massive repair bill.

When we changed our PNW boat's old Raytheon rader to a new Furuno radar some years ago, we had PYI fabricate a short pylon for the antenna to sit on to center it over the existing mount. The pylon is powder-coated aluminum. The mount is stainless steel as were the bolts, nuts, and washers PYI gave us to attach the pylon to the mount. They gave us nylon inserts and washers to isolate the mounting hardware from the aluminum pylon base. Otherwise, the pylon base would have been attacked by corrosion around the stainless mounting bolts and washers.

Another vote for Tef-Gel. I have used it for years on sailboat masts and rigging where stainless steel fittings are routinely attached to aluminum spars. This compound is also widely used by shipbuilders and marine specialists.

There is a quite amazing compound called Tefgel a modified ptfe paste. Expensive but good stops corrosion in dissimalar metals , stainless galling and lubricates as a anti sieze. You should check it out

I have used plumbers tefflon tape with good results.

Sure it will stick a bit , but its fast , easy and the stuff is in your toolbox now.

Otherwise as suggested triple dip (not flash galv) bolts will work .

I've been using Duralac with good results. We were introduced to it when we were in NZ. Duralac is used extensively by spar manufacturers when attaching SS hardware. It was was originally developed for the airline industry.


http://www.llewellyn-ryland.co.uk/downloads/duralac.pdf

Tef-Gel is standard kit on aluminum vessels where SS fasteners are used all the time.

I'm not an electrolysis expert but I'll bet brass is much closer to aluminum on the scale. I just used 32 #10 X 1 1/2 brass screws on a platform I'm building in my stern cockpit and was amazed at the $.55 each cost. Must be because of the copper content of brass. I know they aren't as strong but when I decided on brass I doubled the number of screws.

And I know brass looses it's "bright" appearence quickly.

Copper, salt water and aluminum can be a bad combination.

Brass and and aluminum and salt water... nope, not a good idea, will need Tef gel just like stainless.

Agree, Tef Gel works. Having owned several aluminum boats and have noted that the manufactures recommend only stainless fasteners.

Thanks guys .. that's what I needed to know.

Old Deck,
Yes I remember a friend in Thorne Bay that has a Hewes Craft 18 and they attached stuff w SS fasteners. And there was considerable corrosion right next to the SS. ??

I just used some brass screws in a wood bench (small) in my aft cockpit. Got me thinking about it.

Duralac is used here. Colloquially called "cocky ****" for its similarity in appearance and consistency to bird droppings, messy to use.
Would monel screws overcome the problem? Never heard of aluminum screws, ? too soft.

This thread has me confused... What else would we use but SS steel screws? Aluminum screws? Too soft as a poster noted. I have an aluminum ham radio tower and the factory secured each section with SS screws--been up there for years and no signs of corrosion although I do use anti-seize compound. All my windows in Sherpa use SS screws--no signs of corrosion/electrolysis.

manyboats said:

Thanks guys .. that's what I needed to know.

Old Deck,
Yes I remember a friend in Thorne Bay that has a Hewes Craft 18 and they attached stuff w SS fasteners. And there was considerable corrosion right next to the SS. ??

I just used some brass screws in a wood bench (small) in my aft cockpit. Got me thinking about it.

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Eric,

I wonder about the quality of the stainless they used. Many of us have using stainless for years without a problem.

Ken

OD yes.
There seems to be more different kinds of SS than steel.

Are bronze machine screws readily availible. Wood screws a-plenty but machine screws?

Stainless screws in aluminum will corrode the aluminum and frequently the threads will gall, causing the fastener to fail when you try and undo it. I have some 316 stainless hardware, which is very good but hard to find and expensive. I have some on the boat as the previous owner worked at a pulp mill and I think some of them followed him home. Lucky for me, the mill has closed!

Brass is the wrong alloy for boats, bronze is much better.

The radio tower mentioned is likely not bathed in salt water.

manyboats said:

OD yes.
There seems to be more different kinds of SS than steel.

Are bronze machine screws readily availible. Wood screws a-plenty but machine screws?

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Jamestown has them: Fastener Type: Machine Screws

The only thing I use them for is for fastening bronze fixtures together like through hulls, strainers etc.

In our sail boat days and when we re-rigged the mast on Hobo, in addition to using Duralac, we secured some of the hardware with either ss or monel pop rivets. If remove is (was) required later, all you have to do is drill out the rivet. No worries about the rivet galling like you potentially have with screws.

Xsbank said:

The radio tower mentioned is likely not bathed in salt water.

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Neither are my boat's windows but they do get spray on occassion--definitely not soaking in salt water. The aluminum trim is original and looks great (particularly where SS hardware has been used) and the trim is close to 35 years old. Boat has always been in a saltwater environment. Windows were recently pulled and re-sealed with butyl (original butyl lasted decades before leaking).

Interesting thread...

Stainless steel screws are the proper thing to use. Get the 318 steel ones, Jamestown has them, instead of 316. Wrap them with Teflon tape and put a dab of silicone in the holes if you like. Don't use bronze, brass, or aluminum.

Vashon_Trawler said:

Neither are my boat's windows but they do get spray on occassion--definitely not soaking in salt water. The aluminum trim is original and looks great (particularly where SS hardware has been used) and the trim is close to 35 years old. Boat has always been in a saltwater environment. Windows were recently pulled and re-sealed with butyl (original butyl lasted decades before leaking).

Interesting thread...

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Sounds like the screws were properly bedded.

The screws on my Hatteras are all monel. The window frames are 39 years old and the aluminum windows show little if any corrosion at the screws. Aluminum and stainless don't mix, tef-gel helps but no guarantees. My sailboat masts always isolated stainless from aluminum with vinyl tape or nylon sleeves. There are nylon sleeves specifically made to protect stainless rivets in aluminum. You could rivet your windows with aluminum rivets. They drill out easier than removing corroded screws. If it were my boat I would opt for monel screws. I don't know where they are on the periodic table compared to aluminum, I just know they have held up for 39 years of salt water on my boat.

Very surprised that your aluminum frames are held by Monel screws. Monel is further from aluminum on the galvanic table than even copper, bronze, or brass which we all have seen the results of when in contact with aluminum in a salt environment. Is you boat in fresh water or washed down after each use?

It's 39 years old

Brooksie said:

Very surprised that your aluminum frames are held by Monel screws. Monel is further from aluminum on the galvanic table than even copper, bronze, or brass which we all have seen the results of when in contact with aluminum in a salt environment. Is you boat in fresh water or washed down after each use?

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I've had it for the last 5 years, sails in salt rests in fresh, most of the last 20 years. The previous owner kept the boat in Portage Bay Washington in fresh water. The boat has been all over the place in salt water as far south as Guatamala. I've heard it rains a in Washington and it certainly did in Saint Helens. Down here the sun does more damage than anything. I was told the original screws in the whole boat were Monel. They look like it when I remove them. The window screws I haven't needed to remove yet! I could be mistaken as I really don't know, they just look the same color as the monel screws I've removed. Hatteras actually colored trim screws to match moldings and such.

I think there may be some confusion between the corrosion in the aluminum when in contact with a stainless fastener, usually evidenced by a bubbling in the aluminum surface around the head of the screw, and crevice corrosion of the screw itself due to water intrusion. Monel is less prone to the latter, but should still be properly bedded with something like Tef gel to protect the aluminum from the former. We did a glass re-bed of almost all the windows on my Hatteras, and for the life of me I can't remember if the screws were monel or bronze, but we did bed them when we put the frames back on. The idea of using rivets for this purpose frankly horrifies me, what a mess!

In my opinion, and based on a lot of years' experience with float planes (aluminum) in a salt water environment (PNW), Scary's post 24 is right on the money. I would never trust any sort of insulating gel or paste because the threads of the fastener are going to make metal-to-metal conact no matter how much of the stuff you smear on there or pump into the hole.

If one absolutely has to use stainless fasteners to hold aluminum components, the nylon sleeves mentioned by Scary are the only reliable way to go in my opinion. Even insulating tape seems iffy to me because of the potential for the fastener threads to cut through the tape and make metal-to-metal contact with the aluminum.

I believe the best things to use when fastening things to aluminum or fastening aluminum to things like a cabin side, particulalry in a salt environment, are either aluminum fasteners or galvanized steel fasteners, which are what is generally used in the assembly of the float systems for a floatplane (but not the floats themselves).

The problem with using galvanized fasteners is that the galvanizing disappears with time--- it serves the same function to the steel fastener and the aluminum comonents the fastener is fastened to that zinc anodes serve to a boat. So they have to be inspected at specific intervals and replaced when the galvanizing starts going away, otherwise the steel fastener will start to rust.

Windows in a boat don't seem to me to be a strength item. So I would think aluminum fasteners, be they screws or rivets as Scary suggests, would be the way to go.

Just use Tef Gel or something else to help isolate the SS fasteners and be done with it.

For decades builders and riggers have been doing just that. And as you can clearly tell by the testimonials posted here, it works over the long term.

Galvanized fasteners on a boat in saltwater!?

I would like to thank all here for having a discussion about something i was about to ask about, but was beaten to the draw. I am in the process of rebuilding a swim platform I built for my old Trojan cruiser. The swim platform uses a welded aluminum frame covered with King Starboard. It has served me well over the years, but it has never experienced salt water. I bolted it to the transom with 316 Stainless 3/8" bolts. I can't really say I have experienced any corrosion around the stainless bolts but I do know that aluminum is a sacrificial anode material of choice in fresh water. I hope the Californian makes it to salt water in the next year or two so I wasn't sure what to do about fastening it to the transom. Use the same SS hardware? I was considering asking here but you all beat me to it. I started wandering about connecting the aluminum frame to my bonding system, but quickly concluded that would be the same as using it as a sacrificial anode. Not Good. But the stainless hardware bothered me. My new plan: switch the 3/8' 316 Stainless bolts out for 1/2" Aluminum bolts. The aluminum is weaker at 37,000 psi tensile vs 70,0000 psi tensile for the 316 SS, but the larger size 1/2 vs. 3/8 comes real close to the same overall strength in the end. A Happy Ending. With somewhere close to 24 half inch aluminum bolts holding it to the transom it will be more than adequate and not make me worry about corrosion. It amazes me how much one can learn here by reading the experience of others. The old Trojan was 10' wide beam and the new (to me) Californian 34 LRC is 12' wide. although both boats transoms have a radius, they are not the same. So my plan is to cut the old swim platform in half and spread the halfs to the new wider width and weld a new aluminum section in the middle. In doing so I can adjust the end pieces to better match the Californians transom radius. It is my hope to put together a story about the project in the future.