BYYB Forums

Hi everyone...I finished cutting out all my keel parts and so im thinking more and more about screws...I got a recent e-mail advertisement from woodcraft and they were advertising "stainless steel screws and pins"...

After checking it out I clicked on the info and one portion in the detailed info on the screws says their 305S screws are not recommended for a marine environement...I thought stainless steel was the best?

Here is a link to the info on the screws:

http://www.woodcraft.com/Family/2020614/...nformation

Hope to start laying out the lofting on the boat bottom today...and maybe some other parts like the bulkheads...

Matt

There are lots of different types of stainless steel, many are not suitable for the marine environment. You should be looking for the "7000" series steels.

In fact 305 is the lowest work hardening of all the austenitic stainless steels. It was developed for specifically for use in "drawn" parts (eye bolts, barrel bolts, rivets, etc.) and screws. This stuff will gall faster then you can say the word if you machine fasten.

As far as stainless steels go, this stuff has it's uses, but not in boats. 316 or better yet 316 L are the preferred choices. They can also gall badly, so be careful if you machine drive them. They also can work harden which will make them brittle or easy to fatigue. It's stronger the 304 (another common stainless) but more brittle.

If you are going to be in fresh water all of the time, then you can get by with 304, but it will eventually rust on you. 316 or 316 L will remain bright for decades if cared for (my 1960 Chris Craft, still has bright 316 L stainless on it).

To find the better grades of stainless take a little magnet with you. Run the magnet through the fasteners you're about to buy. If you feel the screws (or what ever) stick to the magnet, it's not good stainless and should be avoided.

Yes Paul, you mentioned that magnet trick a few years back. I do exactly that before i buy any stainless for the boat. thank's for that yet again.

Brian.

Ok thanks Paul...that is good info...assuming the price goes up as the screws get better...

I had many stainless steel screw heads shear off when putting them in. I had to pilot drill the holes first. Not so much trouble using zinc coated screws, they seem to be stronger, and less expensive. Just my experience during the build.

Greg

Zinc plated screws are mild steel, not stainless and will rust fairly easily, even though they're not supposed to. Fresh water boats can tolerate zinc plated screws, but eventually it will become "iron sick" as the moisture in the wood does it's nasty deed, often with the heads looking fine, but the body of the screw wasted away. Zinc near salt water will rust right away.

Galling and work hardening are common issues with stainless. If you machine drive a stainless screw, it must be done painfully slow or you will tear off the heads of smaller fasteners. A screws need a pilot and clearance hole, plus a counter sink is needed. Machine screws and bolts also need to be driven very slowly or the gall. I've torn off the heads on 3/4" bolts fairly easily using impact drivers and big drills on stainless fasteners. If you go slow, and/or us a moly based lubricant, you'll have much less trouble.

This all jives well with our experiences. Stainless is an odd material at times. I've seen several parts of high quality stainless (prop shafts, bolts, t-buckles) waste away due to oxygen starvation, an odd phenomenon which leaves even the nicest stainless like potmetal or ratty iron.

BTW, Stevenson Projects is about to start selling screws also, followed by hardware kits for standing rigging and running rigging this Summer.

M

ooh...sounds good mike...any suggested sources for now? 

Greetings,

I bought my screws and glue from Jamestown Distributors.


http://www.jamestowndistributors.com



316 Stainless Steel

#8 = http://www.jamestowndistributors.com/use...316+S%2FS+

#10 = http://www.jamestowndistributors.com/use...316+S%2FS+

On the right hand side of the page is a [ Select Product ] grey box where you can choose the length ... ie 3/4", 1", 1 & 1/2", etc. These screws were designed to hold plywood (note the shortness of the non-threaded shank), and are not cheap, running about 18 cents each.  If that's too much money, and you are going to be a fresh water only day sailor, then they also carry the same screws in 18-8 stainless for half the price.  As always, you get what you pay for.

Somewhere I picked up a set of combined drill and countersinks (probably from Jamestown) that exactly fit these screws so that the screw point just bottoms out in the hole as it pulls the plywood tight to the stringer.  I have been driving these screws with a new Makita Lithium Ion powered cordless drill / screw driver with the clutch set to #22, so that the clutch slips just as the screw head dimples the top layer of plywood ever so slightly.  I have drilled+countersunk and driven about 600 screws this way, and have yet to break one.

Mention that you are a Back Yard Yacht Builder, and they might still be giving a Discount.

Cheers,
Tom