Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 05-11-2010, 06:30   #1
Registered User

Join Date: Nov 2010
Posts: 13
Mixing Metals Beneath the Waterline - Facts / Myths ?

I am about to install some brass thru-hull fittings complete with sea-cocks and was wondering if mixing metals below water was a problem. I have my sacrificial zincs in place and have heard that "mixing metals" beneath the water could cause the brass to degrade since stainless is also present. I am beginning to think that my sources are not altogether reliable.
__________________

__________________
James Dieterich is offline   Reply With Quote
Old 05-11-2010, 07:05   #2
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29 49.16 N 82 25.82 W
Boat: Pearson 422
Posts: 12,388
Hi James,

First, the through hull fittings should be bronze and not brass. Brass is absolutely not suitable for any below water applications. Brass alloys are primarily copper and zinc and zinc as you know is used as a sacrificial metal and is one of the first to go. Bronze alloys are mainly copper and tin (marine bronze alloys usually have silicon, manganese or other components as well) and are what you should use.

The terms brass and bronze are often misused and the alloys look the same to me in a visual inspection. If you purchased the through hulls from a reputable marine supplier they should be bronze.

All that being said, it is no myth that mixing different metals can and will result in a galvanic reaction that will eat away one of the metals. A galvanic reaction is essentially a battery, two different metals in an acid environment. In a boat this could be zinc and steel in a seawater (mild acid) environment. How much and how fast one of the metals is "eaten" depends on the two different metals or even different alloys of the metals. There are dozens of different bronzes and also stainless steels, some with very different levels of galvanic activity.

The whole issue can be quite complex, to the point that whole books are devoted to the subject and many marine engineers make a career out of the study. For the common sailor following the common precautions is usually adequate.
__________________

__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 05-11-2010, 07:22   #3
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 3,594
Quote:
Originally Posted by James Dieterich View Post
I am about to install some brass thru-hull fittings complete with sea-cocks and was wondering if mixing metals below water was a problem. I have my sacrificial zincs in place and have heard that "mixing metals" beneath the water could cause the brass to degrade since stainless is also present. I am beginning to think that my sources are not altogether reliable.
It is quite common to see bronze thru-hulls used on boats with other fittings made of stainless or other material. In fact, it would somewhat unusual if this were not the case. Go ahead and install your new thru-hulls with confidence, but of course, be sure to keep the boat protected with the proper compliment of sacrificial anodes.
__________________
fstbttms is offline   Reply With Quote
Old 05-11-2010, 07:27   #4
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
since a lot of underwater through hulls are actually bronze skin fittings and a brass ball valve, it will last a considerable time, especially in a GRP boat.

Its not as good as a fully bronze sea cock, but it works

Dave
__________________
goboatingnow is offline   Reply With Quote
Old 05-11-2010, 07:37   #5
Registered User
 
svHyLyte's Avatar

Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,434
Images: 25
My grandfather used to say that brass had no place on a ship save bells, buttons and bugles.

Brass is an alloy of Copper and Zinc and, of course, zinc is the sacraficial metal of choice below the water-line. Bronze is an alloy of Copper and Tin (save for what is commonly known as "Commercial Bronze" which is really Brass by another name) but may also have other eliments added including Silicon which makes for a particularly sturdy Bronze alloy. While you will not find brass fittings in a marine supply store, you might easily find them in a Home Depot or Lowes and it would be unwise to attept to use them aboard ship.

FWIW, the effects of immersing dissimilar metals in an electrolyte (battery technology) has been known since at least 2000 BC (google "Bagdad Battery") but for the sake of the exercise, immerse a piece of brass and a piece of stainless or other metal in a cup of water with a little salt or vinegar mixed in and measure the voltage/potential between the two with a multi-meter. (Metal plating is based upon this phenomena and illustrates the extent to which one metal is wasted by immersion in an electrolyte with a dissimilar metal.)
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
svHyLyte is offline   Reply With Quote
Old 05-11-2010, 07:45   #6
Senior Cruiser
 
osirissail's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: A real life Zombie from FL
Boat: Gulfstar 53 - Osiris
Posts: 5,416
Images: 2
Simply put do not use brass fitting where sea water is involved. Bronze or stainless steel or Marelon are all acceptable. And more importantly each through-hull and seacock must be properly installed/supported so that sudden shear loads will not break them.
__________________
osirissail is offline   Reply With Quote
Old 05-11-2010, 07:49   #7
Registered User
 
capn_billl's Avatar

Join Date: Aug 2010
Location: Houston,Tx
Boat: Maxum 37'
Posts: 1,587
Since water is the universal solvent anything you use will only last a matter of time. Galvanic corrosion can eat a metal part to failure in less than a year. Or a properly protected bronze part can last for over a decade. I have used brass fittings, but they didn't last as long as bronze, and I wouldn't trust them for any distance from shore. Stainless is a good metal, but some grades of stainless are subject to pitting and can fail suddenly. My recommendation, pick a metal, stainless or bronze. use it everywhere. Ground to sacrificial anode. Marine hoses often have a wire threaded into hose material. Bend the end under the hose clamp to ground both ends, (pump to thru hull). ground pump case. Insure sacrificial anode is connected to ground system. Inspect any wet surface often for pitting and signs of corrosion. Test thru-hull valves often. Follow all ABYC recomendations for boat wiring an plumbing, good luck.
__________________
capn_billl is offline   Reply With Quote
Old 05-11-2010, 08:10   #8
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
I just wanted to make a minor correction. An electrolyte is a liquid that can conduct electrons. It is not necessarily an acid such as in the case of salt water, which is slightly above a pH of 7 (slightly basic).

Also mixing various metals underwater is not necessarily a recipe for disaster. I run a boat with an aluminum hull with bronze propellers which are attached to a stainless steel shafts. The shaft is then bolted to an iron transmission and engine block. The electrolysis is under control.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 05-11-2010, 08:21   #9
Mooderator
 
capngeo's Avatar

Cruisers Forum Supporter

Join Date: Jul 2010
Location: Key West & Sarasota
Boat: Cal 28 "Happy Days"
Posts: 4,211
Images: 12
Send a message via Yahoo to capngeo Send a message via Skype™ to capngeo
I remember once (a long time ago) when I worked in a boat yard; a boat got hauled and the bottom paint was burned clean off around each through hull fitting! The copper in the paint was less noble than the stainless through hulls, and became the anode!

About 20 years ago, a salesman talked me into (by giving me free samples) going with the "new" nylon/glass fittings. Well, they are still in service and have required zero maintenance. Any time I have to service one of the metallic ones, it gets replaced by "plastic" now
__________________
Any fool with a big enough checkbook can BUY a boat; it takes a SPECIAL type of fool to build his own! -Capngeo
capngeo is offline   Reply With Quote
Old 05-11-2010, 09:14   #10
Senior Cruiser
 
osirissail's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: A real life Zombie from FL
Boat: Gulfstar 53 - Osiris
Posts: 5,416
Images: 2
The only approved below the waterline fittings are the Marelon series from I believe Australia and sold in the USA by Forespar. I replaced all my through-hulls and sea-cocks with them during a major re-fit for two reasons: 1 - They are not subject to electrolysis and lightning damage; and 2- with all my plumbing being non-metallic I can use acids to clean out sea-growth clogged hoses, pipes and other fittings.
- - But you need to install any through-hull/seacock correctly and be sure it is adequately supported for shear loads. Be your fittings metal or Marelon if improperly installed you are asking for trouble so still keep those wooden cone plugs handy.
__________________
osirissail is offline   Reply With Quote
Old 05-11-2010, 10:05   #11
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Exercise your Marelon valves frequently before they seize up. You can only put so much torque on a plastic handle before it busts off.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 05-11-2010, 10:57   #12
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,592
Images: 240
Greetings and welcome aboard the CF, James.

Mixing metals below the waterline can be a problem.
It's doubtful that you will be using BRASS thru-hulls - much more likely BRONZE.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 05-11-2010, 13:55   #13
Senior Cruiser
 
osirissail's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: A real life Zombie from FL
Boat: Gulfstar 53 - Osiris
Posts: 5,416
Images: 2
Quote:
Originally Posted by David M View Post
Exercise your Marelon valves frequently before they seize up. You can only put so much torque on a plastic handle before it busts off.
Definitely, and that applies to all other types of seacocks especially bronze. However, Marelon have a very neat way of freeing up the ball valve/handle. The handle is not the most rigid and it is easy to snap it off. But each Marelon seacock is made of three main parts: the body base; a ball valve/handle; and the upper body. The body is in two parts with threads holding them together to exert force on the ball/handle. If the ball/handle will not move due to lack of exercise, you can place large wrenches/spammers/channel-lok pliers on each part of the body and "unscrew" the body parts a fraction of a turn. This relieves the pressure on the ball/handle and now you can move/exercise the unit.
- - Anything bronze/SS/Marelon when left in one position for a very long time without exercise tends to "stick" and resists movement. Lubrication during haul-outs should be a must-do on your check-list of things to accomplish before going back into the water.
__________________
osirissail is offline   Reply With Quote
Old 05-11-2010, 14:21   #14
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Quote:
Originally Posted by James Dieterich View Post
I am about to install some brass thru-hull fittings complete with sea-cocks and was wondering if mixing metals below water was a problem. I have my sacrificial zincs in place and have heard that "mixing metals" beneath the water could cause the brass to degrade since stainless is also present. I am beginning to think that my sources are not altogether reliable.
James,

It is quite unlikely that your thru-hulls are made of "brass". If you bought them from a reputable vendor they will likely be 85-5-5-5 bronze or ASTM B62 bronze. In the US, you don't say where you are, Groco, Spartan, Aopollo/Conbraco, Buck Algonquin and others make marine UL rated thru-hulls and seacocks/valves.

You would be best served to stick with a Marine UL product for thru-hull, valve and hose barb. They yellow brass or Muntz Metal valves and hose barbs you buy at Home Depot, and West Marine too, can contain 35-40+% zinc! Dezincification of cheap brass valves or fittings is very real. A true UL marine rated seacock, hose barb or ball valve should have less than 5% Zn.

Also remember that most thru-hulls are generally NPS thread and ball valves are NPT thread which are technically incompatible threads, yet they screw together. When you say "seacocks" I heva no idea whether you mean a thru-hull with a ball valve or a true flanged seacock.

Here's ABYC's suggestions:

27.5.4 Seacocks shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings
and Sea-Valves.

27.5.5 Thru-hull fittings shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull
Fittings and Sea-Valves.

27.6.1 A seacock shall be securely mounted so that the assembly will withstand a 500 pound (227 Kg)
static force applied for 30 seconds to the inboard end of the assembly, without the assembly failing to stop
the ingress of water.

27.6.1.1 The installation shall prevent any movement of the assembly.

27.6.1.2 Thru-hull fittings and seacocks shall be connected directly.

27.6.1.3 Threads used in seacock installations shall be compatible (eg. NPT to NPT, NPS to NPS).


This is the result of mixing marine rated 85-5-5-5 bronze and a Home Depot yellow brass ball valve. The ball was COMPLETELY gone in less than a year, 8 months total in-water time. The thru-hull was like new as were the other bronze marine seacocks on this boat. This valve was a few weeks away from failure, at best.



Oh and a bronze elbow and yellow brass hose barb. Can you say sink your boat...



Brass & Bronze:


Look for the Marine UL logo!



Why not to mismatch threads:
__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Old 05-11-2010, 14:36   #15
Senior Cruiser
 
osirissail's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: A real life Zombie from FL
Boat: Gulfstar 53 - Osiris
Posts: 5,416
Images: 2
To add to Maine Sail's excellent photos - here is a link to the subject of dezincification in boat through-hulls and seacocks - www.michel-christen.com/2T-H.pdf
The photos are in the first half of the paper.
__________________

__________________
osirissail is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Facts and Fiction on US Registration and RCD Dertien Dollars & Cents 3 12-04-2010 20:59
What's Best for Polishing Metals? John Drake Construction, Maintenance & Refit 32 26-06-2009 20:44
Loud crackling beneath waterline - help! KodiakMike Construction, Maintenance & Refit 36 12-12-2007 15:48



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 22:54.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.