A2, A4, 316 steel keellbolt nuts? Help!

[pete]

Hi,
well I'm just getting around to casting and fitting my lead keel, and
I'm using 316 steel bolts ( I know some people disagree but if its
good enough for Van der Stadt its good enough for me!)

So I have ordered the rod and will have a thread cut for the bit that
sticks into the boat, but now my suppliers are offering me A2 nuts to
fit the thread and hold it to the hull.
Does this sound good enough? Should they be A4- or do I have to get
nuts made from 316 steel too?
What is the differnce between A2, A4 and 316 anyway?
Hoping someone can clear a little confusion here.

Pete

[Glenn Ashmore]

I would go with stainless. Think about it. The nuts and washers will be in
the bilge and exposed to rain water, sea water, gray water, and all the
other gunk that ends up down there. You can get them from McMaster.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"pete" <l...@nothere.net> wrote in message
news:kvar339s52s29lp18...@4ax.com...

[Martin Schöön]

pete <l...@nothere.net> writes:

A2 and A4 are designations I am used to see here in Sweden.
A4 is the stuff you want on a boat if you want to avoid rust.
It is also very strong. A2 is not quite as stainless. If the
difference is merely about looks or if there is more to it I don't
know. I have to look it up.

316 is an American designation I think. How it relates to A2 and A4
I don't know. There are conversion tables that should tell you.

--
Martin Schöön "Problems worthy of attack
show their worth by hitting back."
Piet Hein

[David Scheidt]

Martin Sch??n <martin...@gmail.com> wrote:

:A2 and A4 are designations I am used to see here in Sweden.

:A4 is the stuff you want on a boat if you want to avoid rust.
:It is also very strong. A2 is not quite as stainless. If the
:difference is merely about looks or if there is more to it I don't
:know. I have to look it up.

:316 is an American designation I think. How it relates to A2 and A4
:I don't know. There are conversion tables that should tell you.

A2 is 304 -- 18% chromium, 10% nickel. A4 is 316, 18% chromium, 10%
nickel, 2% molybdenum.

[Steve Lusardi]

Pete,
The DIN designation A2 is about the same as AISI 304 and DIN A4 is
equivalent to AISI 316. There are also variants 316 L (2% Molybdenum) and
316 TI (Titanium). Both A4 and 316 have superior anti corrosion properties
over A2 and 304. The 316 variants have even better anti corrosion properties
and are primarily directed at the chemical industry. Type 304 / A2 are used
in fresh water environments and A4 / 316 in salt water. As far as strength,
all stainless bolts have less strength than a Grade 8 high strength bolt,
but slightly better than a Grade 5. Most stainless fasteners are made from
8-18. This variant has the corrosion resistance of A2/304, but has superior
strength.

In application, stainless bolts used in threaded stainless holes(nuts) have
a high tendency to gall and seize under load. Try not to do this. If the
threat of corrosion is significant, use a different alloy nut than the bolt,
never use 304 with 304 or 316 with 316 and always use an anti-seize grease.
Understanding the corrosion failure mode of stainless is very important as
well, before deciding on its use. Stainless steel relies on absorbing free
oxygen on its exposed surface not to corrode. If a stainless bolt is exposed
to stagnant water AND is subject to even the slightest working motion where
the surface is rubbed, the surface oxygen will be removed. The surface will
then attempt to re-absorb free oxygen from its environment. As long as its
environment has free oxygen, its corrosion resistance will continue.
However, if the environment now has a depleted supply of free oxygen, then
crevice corrosion starts and it is very rapid.

So the gamble is the bolt never gets wet or is continually flushed with new
water or the bolt never moves after installation. In the case of keel bolts,
your odds are not good for a favorable environment. Remember "Drum" in the
Solent in the '80s or the British gentleman in the BOAC off the coast of
Australia in the '90s. These are the ones we hear about. It's very difficult
to report a failure when you're dead and the boat is sunk. I love stainless,
but not for keel bolts, Van der Stadt or otherwise. Think wrought iron,
manganese Bronze or even Silicon Bronze, but not stainless.
Steve

[pete]

Thanks for your replies, I did think that A4 was equivalent to 316
but was nver sure and am pleased some people confirmed it.

Steve, thanks for your input, you did press this point on to me (and a
few others I believe) before, and I hear what you are saying,, I am
going to see if I can find suppliers of the alternatives, but how
would this affect the size of the bolts? For example, for my keel, the
architecht has specified 20mm diameter steel, need this be increased
if using bronze?

I do vividly remember Drum, plus a few others, the most recent being
Hooligan V a few months ago in the UK with the loss of a crewman, but
that, in fairness, was a case of the keel itself snapping in two at
the point of entry into the "letterbox" slot in her hull.

Ta very much, Pete

[Steve Lusardi]

Pete,
Out of all 3 alternatives, I would use wrought iron. There are iron plated
ships still in service in excess of 100 years old. Bronze is OK if you do
not have other metals in use below the waterline. Iron is non-homogeneous
(it is not an alloy) (no internal batteries) and is the least reactive
electrolytically. In all cases I would increase the rod size to 30mm and not
worry about them forever. Use plenty, it's cheap insurance.
Steve

"pete" <l...@nothere.net> wrote in message

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