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Old 07-10-2008, 21:43   #136
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Oh, and I did also want to mention that after we put the mast back in, we went for our first weekend of sailing and ended up beating into a gale with gusts of up to 79 knots (photographic evidence exists).... thats one way to test out your rig-tuning, but not the way I would have chosen... we also got to test our anchor's holding power in up to about 60 knot gusts... again not the recommeded test protocol...


N.B. There is no "wrong" advice posted on an Internet Forum. All advice is personal opinon, and should be considered in that light. I never treat such advice as gospel, nor do I discount it out of hand. Discussing the various sides of an issue is interesting in itself, irregardless of whether one's own opinion is changed in the process.
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Old 07-10-2008, 22:01   #137
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Oh, and I did also want to mention that after we put the mast back in, we went for our first weekend of sailing and ended up beating into a gale with gusts of up to 79 knots (photographic evidence exists).... thats one way to test out your rig-tuning, but not the way I would have chosen... we also got to test our anchor's holding power in up to about 60 knot gusts... again not the recommeded test protocol...
.......
In Storm Bay or somewhere else??????
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Old 07-10-2008, 22:02   #138
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You may be interested in "Barnacle Bill" an ex 1970's NZ Admiral Cup boat converted to a cruising vessel - Barnacle Bill - Sparkman and Stephens Racer Cruiser From New Zealand .
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Old 08-10-2008, 04:45   #139
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True enough but the story is not that simple. Ships use duplex or moly SS and have fairly complex cathodic protection with good electrical connectons.

Most folks are lucky to get the rig in the boat square, think they can develop and maintain good cathodic protection for 316 in stagnant saltwater?

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SS is fine Weyalan, some of the advice you are getting here is very poor and just repeats the myths promulgated on amateur forums made from uninformed positions. SS is widely used on high quality vessels and on well fitted commercial vessels for seacocks etc (cos they can afford it, wish I could ). It is an especially convenient material for aluminium vessels.
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Old 08-10-2008, 13:10   #140
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True enough but the story is not that simple. Ships use duplex or moly SS and have fairly complex cathodic protection with good electrical connectons.

Most folks are lucky to get the rig in the boat square, think they can develop and maintain good cathodic protection for 316 in stagnant saltwater?
You mustn't jump to conclusions - I was not referring to ships at all.

You seem to have a misconception as to the exact nature of any problems with ss's in "stagnant seawater" - I suggest that you go away and do some study on the matter before freely offering advice (sic) on it.
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Old 08-10-2008, 13:41   #141
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Midland, there are many citations of research done on crevice corrosion of 316SS in seawater. Here's the Google cached page of one that appears to have been removed from public access and moved to a restricted military venue:

This is Google's cache of http://stinet.dtic.mil/oai/oai?&verb...fier=ADA315900. It is a snapshot of the page as it appeared on May 10, 2008 11:38:28 GMT. The current page could have changed in the meantime. Learn more

Text-only version
These search terms are highlighted: crevice corrosion 316 stainless



Defense Technical Information CenterAccession Number : ADA315900
Title : An Analysis of Possible Microbiologically Influenced Crevice Corrosion of 316 Stainless Steel in a Seawater Environment.
Descriptive Note : Master's thesis,
Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF OCEAN ENGINEERING
Personal Author(s) : Howell, William R., Jr
Handle / proxy Url : Check NTIS Availability...
Report Date : SEP 1996
Pagination or Media Count : 66
Abstract : An analysis was conducted of 316 Stainless Steel components which exhibited an unusual degree of crevice corrosion after exposure to seawater for approximately one year. After conducting research into the possible chemical and microbiological mechanisms for the corrosion, a metallurgical and microscopic examination of the components was performed. Results of these examinations indicated that the corrosion observed was probably the result of an interaction between the Gallionella aerobic iron bacteria and the anaerobic sulfate reducing bacteria Desulfovibrio and Desulfomaculum.
Descriptors : *STAINLESS STEEL, *CORROSION RESISTANCE, *SEA WATER, *MICROBIOLOGY, *METALLURGY, ENVIRONMENTS, CORROSION, EXPOSURE(GENERAL), CRACKS, MICROSCOPY, IRON, CHEMICAL REACTIONS, MEDICAL EXAMINATION, AEROBIC BACTERIA.
Subject Categories : MICROBIOLOGY
PHYSICAL AND DYNAMIC OCEANOGRAPHY
PROPERTIES OF METALS AND ALLOYS
Distribution Statement : APPROVED FOR PUBLIC RELEASE


Search DTIC's Public STINET for similiar documents.

Members of the public may purchase hardcopy documents from the National Technical Information Service.


Other citations don't mention bacterial involvement, but the topic itself is taken seriously by a number of sources you probably wouldn't have any problem accepting. Including the US Department of Energy, (DOE) which is concerned about failures in nuclear cooling and storage systems where 316SS has been failing from crevice corrosion with questions as to whether the effects are galvanic, chemical, or some combination.

Reasonable men can and do sometimes disagree. A significant number of them, with scholarly credentials and field experience, have reported failures in stainless and advised against its use in certain situations. You think they're all wrong? You're entitled to your opinion, but some of us would be more impressed if you could demonstrate any flaws in their concerns, or disprove the theories they suggest for the failures. Saying "it ain't so" without going any further, contributes nothing to the discussion. Please, do tell us why they are all wrong and why you believe 316SS in damp anoxic conditions is a structurally suitable and stable material.

A closed seacock, containing several ounces of seawater and simply sitting, closed, at dock or during layup as typical of yachts, is a perfect example of the conditions they say will promote failure. An open seacock, with seawater actively flowing through it, is not the issue here.
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Old 08-10-2008, 14:01   #142
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If it has the pinched up stern (to meet the IOR rule) it will roll bad on a reach. Nothing wrong with a light , well built boat though. IOR boats should be cheap on the market though. Sure you aren't paying too much?
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Old 08-10-2008, 14:18   #143
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Midlandone, please explain to all of us how 304/316/316L can remain in salt water without any corrosion. I'm always open to learning something new.

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You mustn't jump to conclusions - I was not referring to ships at all.

You seem to have a misconception as to the exact nature of any problems with ss's in "stagnant seawater" - I suggest that you go away and do some study on the matter before freely offering advice (sic) on it.
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Old 08-10-2008, 16:32   #144
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In Storm Bay or somewhere else??????
Believe it or not, in the Derwent itself, blowing norwesterly. We got laid flat and "gave the spreaders a wash" right off nutgrove. That was a gust that we saw at 63 knots, Pisces, just ahead of us, got a photo of 69 knots on their instruments, and the Hobart Ports tower registered at 82 knots!

Last night was the first twilight race of the season (yay). I love twilight races... low stress (no spinnakers), good fun, not too long (3 beer races, generally). We came 2nd in div 1 (4th across, beating several "faster" boats)
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Old 08-10-2008, 16:45   #145
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Midlandone, please explain to all of us how 304/316/316L can remain in salt water without any corrosion. I'm always open to learning something new.

Professional BoatBuilder - July/August 2008
You might like to point out where I said ss "can remain in salt water without any corrosion" - as I did not say it and you are repeating your error of making assumptions about or making fabrications of what I have said.

In fact I find your question interesting because ss (and a number of other metals) rely on corrosion to build a protective layer. As way of another example aluminium is simlilar and is also another metal for which the correct alloys are ok uncoated in seawater.

As for the article you referred to the writer has made a glib statement covering ss. As with bronzes there are alloys of ss that are resistant (and widely used) and alloys that are not. With bronzes they are all at least reasonably resistant as long as low presence of zinc - remembering that the widely used manganese bronze is actually an alloy with zinc so a brass not a bronze but in low beta phase is resistant. It is, of course, the common bronze (brass) in propellers and also widely used in seacocks.

You will find that many ball type bronze seacocks (maybe some plug ones too) actually have ss balls in them and many well respected bronze seacocks are actually made of brass - eg Blakes are made from alpha phase manganese bronze, a brass. Manganese bronze if not carefully cast and so of high beta phase will give severe problems as owners of lower quality propellers, for example, often find out through dezincification unless they provide heavy anodic protection to them.

In the end, ss is widely used on high quality boats and high quality pleasure boats with no problems including for seacocks. As I have said, ss becomes an especially sensible solution for aluminium boats. If you think the designers and builders of these vessels don't know what they are doing I suggest that you go and give them the advantage of your knowledge instead of fabricating words into my mouth here.

Hellosailor - I have never claimed that crevice corrosion cannot exist and don't need it explained to me. I have been exposed to problems with ss (and other metals) since the early 1970's when involved with ss in situations which make seawater seem tame (eg boiling water and preciptated chlorides from wetting drying cycles resulting in tank failures from crevice corrosion in way of welds and residual stresses in plating). As in all things correct selection of alloy and manufacture is important - ss doesn't have that on its own, bronzes do too, for example.

In the end ss (of correct grades) is fine underwater and is widely used. It is also (of correct grade) also fine in temporary anerobic conditions. It is not a wise choice in permanent anerobic conditions in seawater such as the bottom ends of moorings.

But in the end I see that the forum myth will be told and retold from uninformed mouths that ss is not suitable for seacocks or through hulls/standpipes - that despite its widespread use (its use including, it seems, by several well informed forumites here ). Also enough has been done to stuff up Weyala's thread (but maybe he has more comfort in his choice of seacocks).

So I will leave it at that, at least some understand the message that I deliver.
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Old 08-10-2008, 17:44   #146
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I do not consider the thread in the least bit "stuffed-up". I'm learning stuff: Learning stuff is good!
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Old 08-10-2008, 18:00   #147
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Believe it or not, in the Derwent itself, blowing norwesterly. We got laid flat and "gave the spreaders a wash" right off nutgrove. That was a gust that we saw at 63 knots, Pisces, just ahead of us, got a photo of 69 knots on their instruments, and the Hobart Ports tower registered at 82 knots!

Last night was the first twilight race of the season (yay). I love twilight races... low stress (no spinnakers), good fun, not too long (3 beer races, generally). We came 2nd in div 1 (4th across, beating several "faster" boats)
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I do not consider the thread in the least bit "stuffed-up". I'm learning stuff: Learning stuff is good!
63kt knock downs, 2nd in twilight races, 3 beers and we get a 361SS spit fight.

No - Not stuffed up. I'm having a (seacock) ball....
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Old 08-10-2008, 18:01   #148
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Hey Weyalan, good to hear you are back in and sailing. Sorry to muck up your thread.

I think Midlandone and I will have to agree to disagree. Maybe I'll repost in another thread and ask him how he protects 316 from crevice corrosion when used below the waterline?

Anyway, Good Job as always.

Joli
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Old 09-10-2008, 03:07   #149
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Hi Joli - I just noticed that the Professional Boatbuilder article you linked to also says one shouldn't use high zinc brasses for seacocks. Which on the face of it, as a generalisation only, is good advice but is in fact wrong because as I pointed out manganese bronze is actually a brass and is in fact widely used by trusted manufacturers eg Blakes.

So, there you go, one mustn't believe everything you read in magazine articles .

I wonder how you feel about ss keelbolts - widely used and also successful (and under water, including often anerobic ).
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Old 09-10-2008, 10:37   #150
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Boy are we getting Clintonesque in our parsing of words.

As far as brass, if it's called brass and/or is the bright yellow color, steer clear. In the typical brass, the zinc is rapidly eroded leaving a hollow weak copper fitting. Manganese Bronze may be a brass, but it doesn't suffer the zinc depletion that most brass does. So consider it a bronze which is probably why it's called bronze.

SS has problems with crevice corrosion. Still it will work just fine for thru-hulls. Don't expect them to last nearly indefinitely as bronze ones do, however. If SS ones fail to seal, start leaking through the valve, etc. be worried. I'd be thinking of replacing them over time with something that is more corrosion tolerant but I wouldn't panic.

The big thing, is don't go down to the local Home Depot and buy ball valves for your thru-hulls. They are mostly Chinese made with the quality chemistry that their products are noted for. They look good but could be anything from adequate to absolutely unsafe. Have seen photos of HD ball valves that failed within a year from corrosion. For instance, one of their tricks is to use chrome plated steel for the balls in the valve. Impossible to tell for sure what they are made of until they rust and stop sealing.

Last but not least, Marelon is not a set and forget seacock. They need to be cycled regularly or they freeze up. When that happens, the handles typically break off rendering them useless. IIRC, Forespar says they should be lubricated annually. A little difficult to do in the water unless your really quick working in a gusher.

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