"Marine" vs "Deck" stainless steel screws?

[matt167]

I need some screws for my boat build. I know I need brass/ bronze, Monel or stainless fasteners..

I've chosen screws because they will be easiest. 90% of holding will be construction adhesive ( PL Premium or Titebond III depending on area/ holding power needed ).. I can get 1lb boxes of #8 605 stainless " Deck" screws for cheap locally. Marine grade fasteners would need ordered in at a much higher cost. Is stainless stainless?

 

[dingbat]

There are over 300 alloys of “stainless” steel.

I would not use deck screws in a marine environment w/o knowing the alloy.

You would be alright using these https://www.manasquanfasteners.com/product/decking-screws-bugle316/

 

[matt167]

The ones I found are 305 alloy. I put 605 up, but I went back and looked. 305

 

[dingbat]

The ones I found are 305 alloy. I put 605 up, but I went back and looked. 305

305 would be OK to use around freshwater but not saltwater

 

[Scott Danforth]

actually its well over 2500 alloys of stainless

you have the ferritic and austenitic as well as duplex (both ferritic and austenitic)

all with various amounts of iron, chromium, nickel and other metals in them..... .

if your near salt water, you want 316 for the alloy. if you are covering the screws with glass then any of the 300 series would works (and that includes the whole 18-8 family)

many fasteners are in the 18-8 category, some in the 410 series (self drilling) then there is the high strength alloys such as 15-5PH and 17-4PH

 

[dingbat]

I thought it was 150-some, but yeah, it's a lot. Most folks hear stainless and think it's all the same.

Not sure off the top of my head how many “grades” are recognized by SAE, how many

 

[dingbat]

...

 

[Chris1956]

I have had good luck with SS deck screws in the saltwater environment. Those deck screws will be hardened for use with a power driver. Marine screws will be soft, and real hard to drive without drilling pilot holes. The deck screws may (or may not) rust a bit. I would go with the deck screws.

 

[dingbat]

actually its well over 2500 alloys of stainless

Considering any steel containing between 10.5 to 30% nickel is considered stainless, probably a lot more than that world wide. One of our customer rolls over 130 “grades” on one mill alone.

We also work with a number of specialty facilities that produce a large number of proprietary materials for aircraft and military applications. They are technically stainless steels but will never appear in any grade listing

Non-disclosures are the norm to even talk about the material let along divulge the composition information required for us to do our job.

 

[dingbat]

I realize we've gone off topic, but my curiosity required looking into what my memory was recalling. This is what I remembered reading several years ago when researching stainless. This link mentions there are 5 major types or "families" that make up "more than 150 grades of stainless steel." Whether it's accurate or not, at least I know my memory still (sometimes) works :lol:

https://www.shapecut.com.au/blog/how...eel-are-there/

Part of the discrepancy is semantics.There is no clear cut norm on what differentiates a "Grade" from a "Product", let alone start digging into the variations in Chemistry from one "Product/Grade" to the next.

If I harden or anneal a particular "Grade" to impart different mechanical properties, does the material stay the same "Grade" or does it become a "Product"?

Then these is all the proprietary stuff whose chemistry and mechanical properties, or even their existence for that matter, will never be divulged to outside parties.

Lot and lots of work being done to develop the next generation of Stainless Alloys are thinner, stronger and lighter than before.

Been in the industry over 40 years. I still hear or learn about new Grades/ Products on a regular basis

 

[matt167]

I have never actually understood the differences in stainless steel OR aluminum. I was thinking about building the hull of the boat out of Aluminum but I did not want to rivet all those rivets.. It will be fiberglass encapsulated plywood. All of the fasteners should be under a layer of fiberglass.

I bought the 305 grade fasteners, which I guess are also coated with an anti corrosive. These are approved for use in treated lumber so I suspect the coating is to prevent galvanic corrosion associated with dissimilar metals

 

[Tycer]

According to Don Danenberg’s boat building books stainless steel requires oxygen to form a protective oxide coating and should never be used below the water line. My experience in home building trades keeps me away from stainless due to its brittleness. I’ve snapped many a head off. Under water I follow Don’s advice and use silicon bronze. If I’m permanently adhering something that will be submerged it’s 5200 for me.

 

[matt167]

Hmm, since it will be encapsulated with fiberglass I think I'll be ok. The fastener won't be doing much once the adhesive is cured. The reason I will use PL premium vs 5200 is, PL premium is a construction adhesive. 5200 is a sealant adhesive. 5200 has it's place but I think for doing what I need it to, PL Premium will work best. I'm gluing Douglas fir dimensional lumber to exterior plywood. Screws hold it in place while it cures

 

[Chris1956]

If the screws are under fiberglass, SS deck screws will last forever.

Gee, I am not sure who said SS screws cannot be used underwater....every boat builder does it. Silicon Bronze is a fine material, but it is not shiny and boat builders like their boats to have that shine.