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instead of bronze or galvanized screws why not stainless steel

For above the water line stainless steel is OK. Below the water line Silicon Bronze is preferred. Stainless steel when exposed to air forms a protective layer of oxide. When used under water that does not happen which can lead to a type of corrission. There can be savings in sticking with one type rather then mixing because of quanity discounts.

Stainless steel comes in many alloys, some people believe stainless steel is non-magnetic but there are certain stainless alloys that are magnetic. Stainless steel identified as being in the 300 series are claimed to be OK for salt water. If you only go to inland waters stainless is fine. The problem with galvanized screws is if they are electroplated instead of being hot dipped then the sharp edges don't get much, if any, zinc coating. If you want to be a purest then use bronze.

Common hardware stainless is normally 18=8. The step up is a 304 and then 316 which is the prefered metal. On trailable boats with modern glues and materials stainless is really not an issue like you see in in water boats that does not get glassed or sealed with bungs over the heads. Bronze is also suspect since most bronze hardware is suspect, all stock coming from overseas even for the few guys advertising theirs are domestic hardware. The only thing that the states are doing is cutting the threads on solid stock, dependant on the quality. There are also ring shank fasteners using monel which is expensive but well worth it for some serious jobs.

There are indeed magnetic and nonmagnetic alloys...the magnetic ones are fine if you want your kitchen knives to stick to a magnetic rack but they don't really belong in a boat. Like Oyster mentioned, if you're getting it in a hardware store, it's probably 18-8. If you can't find a marine supplier nearby, I'd buck up and pay the shipping to get the right stuff.

I too have heard and read about crevice corrosion in stainless fasteners, but I've done a lot of refits and I don't recall ever seeing a fastener failure where there wasn't some over-riding cause that would also stress a brand new fastener. This includes boats built long before the epoxy formulations that make our lives so much easier.

Like any skipper, you have to be comfortable with your boat and feel she's going to stay together longer than you. However, I also think that it's not a significant enough threat to prevent someone from building and enjoying their boat for lack of hardware. I thin it's safe to say that most of us build boats to be used first and foremost, long-lived is secondary.

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-Brian

"Do or do not. There is no try."
- Yoda

I try to keep things in perspective.

Yes, my silicon bronze hardware (5lb's of nails, about 1500 screws and half dozen carriage bolts) was expensive at a little over 600 bucks for everthing I needed.

But my total build cost is close to 15K - the fasteners accounting for about 4% of the overall pricetag.

It just makes no sense to me to skimp out on fasteners, (that are there afterall to back up a joint in most cases if your glue skills are less than perfect), to do what? reduce the percentage of your overall cost down to 3...

As stated above, the quality of all hardware is crap compared to what it used to be - so why not be as safe as possible and buy the "better quality" crap, at least for something as important as fasteners

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it