Stainless steel running gear

Either you're confused or I am. Old fogeys like me were brought up to
never use stainless below the waterline. Although this rule has been
relaxed somewhat, broadly speaking, stainless is less satisfactory
than bronze -- its advantage lies only in lower cost.

Prop, strut, shaft, and rudder on inboard power boats under sixty feet
or so(which I'm guessing is what we're talking about here) always used
to be made of bronze. This gave good strength, excellent corrosion
resistance, and long life. Bronze has, however, gotten more and more
expensive and stainless has gotten relatively cheaper, so that now it
is cheaper to use stainless than bronze. Bronze is still the more
satisfactory material as it is much more corrosion resistant and is
somewhat stronger, allowing for smaller shaft sizes. (I'm painting
with a broad brush here, as there are many different bronze alloys,
but almost all of them do better than 303/304 or 316 stainless.)

The only time you might be happier with a stainless prop rather than
bronze is after hitting something hard, as the stainless prop might be
less chewed up. Even there, however, it could be debated, as it is
easier and cheaper to rebuild a badly damaged bronze prop than a
stainless one.

As for no-nos, stainless is OK (not great) if you use all stainless.
It's also OK if you use a bronze prop on a stainless shaft -- many
sailboats do this now -- provided you put a shaft zinc on. You're
less likely to want to do this on a powerboat shaft that will spinning
much faster, but electro-chemically it's fine.


Jim Woodward
<a style='text-decoration: underline;' href="http://www.mvFintry.com" target="_blank">www.mvFintry.com</a>


khorn RemoveThis @rhmdc.com (kim) wrote in message news:<a584e1f7.0310081205.2f09412c RemoveThis @posting.google.com>...
 > Can someone tell me the advantages/ disadvantages of stainless steel
 > running gear (prop, strut, shaft, and rudder). I remembered hearing
 > that it was a no-no, but I have nothing to prove either way.
 >
 > A boat I test drove had this installed, and it does'nt make sense why
 > someone would dump all this money into the running gear if it provides
 > no additional structural, corrosion resistance, or performance
 > enhancements.
 >
 > Thanks!<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Stainless steel running gear 

Cannons used to be cast out of bronze too until we learned how to cast
steel. My sailboat has the original SS shaft in saltwater for 25 years
and is doing fine. For a number of years now there have been a
gazillion shafts and props made of SS and I don't recall a lot of
problems with them.

Ron
 >> Stay informed about: Stainless steel running gear 

Thanks for all your input!
Kim
 >> Stay informed about: Stainless steel running gear 

kim wrote:
 > Can someone tell me the advantages/ disadvantages of stainless steel
 > running gear (prop, strut, shaft, and rudder). I remembered hearing
 > that it was a no-no, but I have nothing to prove either way.

 > A boat I test drove had this installed, and it does'nt make sense why
 > someone would dump all this money into the running gear if it provides
 > no additional structural, corrosion resistance, or performance
 > enhancements.
 >
 > Thanks!

Jewelery?

Sailing is a status sport?

Except for the elite. Ask Eienstein.

Replacement cost
/
lifetime
=
Cost effectiveness (more or less)

Vanity is a sin.

Your gavanism may vary. All metals underwater might best be all
the same alloy. Fat chance. Measure millivolts between evey
possible pair with bonding on and off. Decide on zinks / year
later.

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rc
gkoouhg.RemoveThis@ipxbcugs.net<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Stainless steel running gear 

Stainless steels require oxygen (to bind with chromium to form a protective
chromium oxide layer) to work well. And even then they are susceptible to
chloride stress corrosion, crevice corrosion, and galvanic corrosion, especially
in oxygen poor stagnant areas (like inside bearings etc. Bronze is better,
monel or nickel-copper better yet, but all much pr icier.

That said, stainless steel can work satisfactorily but you have to use alloys
specific for the task. Don't use 302/304 series. The 316 series is better but
less strong and have been known to suffer catastrophic failure due to corrosion.
The best SS alloys are expensive and known by various trade names such as
Nitronic 50 or Aquamet 22. Those are the only SS alloys I would consider for
use below the waterline (but be prepared for sticker shock)

JJ


On Sat, 11 Oct 2003 12:15:24 -0400 (EDT), gourt.DeleteThis@webtv.net (Ron Thornton) wrote:

 >Cannons used to be cast out of bronze too until we learned how to cast
 >steel. My sailboat has the original SS shaft in saltwater for 25 years
 >and is doing fine. For a number of years now there have been a
 >gazillion shafts and props made of SS and I don't recall a lot of
 >problems with them.
 >
 >Ron

James Johnson
remove the "dot" from after sail in email address to reply<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Stainless steel running gear