Seacock - bronze or stainless steel?

alex · Post by **alex** » Tue Mar 11, 2008 23:09 pm

Hello,

I am about to install a hose fitting (läpivienti), but fell into material thoughts - what is better, bronze or stainless steel? I would rather pick up steel - it doesn't rust, doesn't corrode, it's everlasting. However, many boats have bronze fittings - there should be a reason. At least, I could cut bronze to the size myself, and cutting stainless steel would be an undesirable project...

Alex

harald · Post by **harald** » Wed Mar 12, 2008 09:16 am

I'm under the impression that stainless could in some cases be
suspectible to pitting, but I'm not the expert. There's prolly a reason
why most thru-hulls are bronze?

Have you thought about a composite thru-hull? It doesn't rust,
corrode and as a bonus it becomes very flush with the bottom of
the boat when closed?

We installed a flowtech thru-hull for all incoming water in the boat and
have been very satisfied with this solution. I think X-yachts and many
other use these as standard?

Start clicking from this picture forwards:

http://www.fe83.org/gallery/view_photo. ... d=im000781

rgrds

Petri · Post by **Petri** » Wed Mar 12, 2008 10:49 am

Do not use stainless steel in boats, ever.
If you want to use steel, check that you are using acid proof steel (haponkestävä).

Like Harald said, composite materials might be the optimal choice.

harald · Post by **harald** » Wed Mar 12, 2008 21:22 pm

http://www.meredin.fi/Meredin/1107.pdf

page 3, the right side.

alex · Post by **alex** » Wed Mar 12, 2008 21:28 pm

harald wrote:There's prolly a reason why most thru-hulls are bronze?

That's what I stumbled upon. I was stainless steel ready but then I recalled most thru-hulls I saw were bronze...

harald wrote:Have you thought about a composite thru-hull? It doesn't rust, corrode and as a bonus it becomes very flush with the bottom of
the boat when closed?

No, I haven't. I don't trust plastic much (old experience), but composite is stronger. Will check the options.

harald wrote:Start clicking from this picture forwards:
http://www.fe83.org/gallery/view_photo. ... d=im000781

Yes, I saw that. FE83 project galleries are fascinating.

harald · Post by **harald** » Wed Mar 12, 2008 21:36 pm

Well, the whole hull is composite, so why shouldn't the thru-hull be?

alex · Post by **alex** » Wed Mar 12, 2008 22:41 pm

Petri wrote:Do not use stainless steel in boats, ever.
If you want to use steel, check that you are using acid proof steel (haponkestävä).

Well, I thought all boat stainless steel stuff is acid proof...

alex · Post by **alex** » Wed Mar 12, 2008 22:42 pm

harald wrote:Well, the whole hull is composite, so why shouldn't the thru-hull be?

Perhaps since hull has no small moving parts...

Petri · Post by **Petri** » Thu Mar 13, 2008 10:36 am

alex wrote: Well, I thought all boat stainless steel stuff is acid proof...

Some are, some are just marketed as "rosteri" aka. stainless. The problem is that some of the spare parts e.g. are made for inland boating, so acid proofness isn't needed.
The point is just always to make sure that you are really buying acid proof, not just stainless.

jukkaa · Post by **jukkaa** » Thu Mar 13, 2008 12:46 pm

Petri wrote: The point is just always to make sure that you are really buying acid proof, not just stainless.

The stainless steel through-hulls and seacocks that e.g. Maritim sells seem be made of AISI 316 steel, which should be "acid proof", AFAIK.

I would be very interested in the real reason for using brass instead of stainless steel. The brass seacocks seem to be prone to jamming, especially when used as the toilet overboard dumping valve.

Jukka

Panu · Post by **Panu** » Thu Mar 13, 2008 12:48 pm

Petri wrote:
alex wrote: Well, I thought all boat stainless steel stuff is acid proof...
Some are, some are just marketed as "rosteri" aka. stainless. The problem is that some of the spare parts e.g. are made for inland boating, so acid proofness isn't needed.
The point is just always to make sure that you are really buying acid proof, not just stainless.

Hello Sailors

Normal austenitic staniless steel (AISI 304) is not suitable for sea use below water line. Above the water line stainless steel must be polished and waxed propely to tolerate clorine content of the atmosphere.

To be sure that not to have any corrosion you should use acis proof steel (AISI 316). This is austenitic steel, but there is 2-3% Mo content in it, witch increase tolerance against corrosion. We have to understand that acid proof is just acid proof by definition. It doesn't mean that you can use it in any kind of environmet without problems. For example in pulp industry you can find so hostile environmet that AISI 316 can tolerate it less than 30 min

. Normally AISI316 is OK, even under the water line.

Both AISI 304 and 316 are sold as L versions (AISI316L) witch means low carbon content. This makes material more tolerant against corrocion after expose to exessive heat like in welding process.

If you whant to be on safe side (overkill attitude) you should use dublex (austenic-ferritic) stainless steel (AISI 329) or even more pregious materials like super budlex or inconels etc. These materials are extremely difficult to handle or work with. Even drilling a hole can be a huge challenge

. Also the price could be obstacle for use.

Olli · Post by **Olli** » Thu Mar 13, 2008 14:19 pm

Panu wrote:Normally AISI316 is OK, even under the water line.

So, if you would replace thru-hulls, would you use AISI316 or brass? Couple of years ago when I replaced all thru-hulls I figured that the brass ones will last at least as long as my hull epoxy treatment, and when (or if) I have to renew the epoxy treatment again, I will remove the thru-hulls anyway, because it makes the bottom job easier.

This part is for Finnish readers (cannot be translated): Haponkestävän teräksen lisäksi on olemassa myös **tun kestävä teräs, jota käytetään mm. strippiluolien tangoissa. FE:n alumiininen strippitanko soveltuu vain tilapäiseen käyttöön

alex · Post by **alex** » Fri Mar 14, 2008 18:34 pm

Thanks to everybody. Have got lots of interesting information about materials.

jarno · Post by **jarno** » Sat Mar 15, 2008 01:33 am

I would think it is unnecessary to use high strenght materials as AISI304 or AISI316 in through hull's. They both have a tendecy to jam the threads. Brass as a softer material is more feasible and still harder than surrounding material (glassfibre). Get less jammed pipe connectors.. use brass.

alex · Post by **alex** » Sun Mar 16, 2008 13:58 pm

jarno wrote:I would think it is unnecessary to use high strenght materials as AISI304 or AISI316 in through hull's. They both have a tendecy to jam the threads. Brass as a softer material is more feasible and still harder than surrounding material (glassfibre). Get less jammed pipe connectors.. use brass.

Yes, I think so too - contacting part materlais should be comparatively equal in rigidity.