mixing metals

[redhead78]

Hello, I have a question reguarding compatability of metal. I am installing a groco Bronze tri fllange seacock base. Can I use stainless steel 5/16" bolts to secure to the hull? Can I mix these metals without a problem? thanks Red

 

[Maine Sail]

Hello, I have a question reguarding compatability of metal. I am installing a groco Bronze tri fllange seacock base. Can I use stainless steel 5/16" bolts to secure to the hull? Can I mix these metals without a problem? thanks Red

It is not advised. Stainless suffers from crevice corrosion and would not be the best choice for that application. You'll want to try and find some bronze. Hamilton Marine can ship you what you need, they stock it. Just buy them long and cut to length if you are not sure. Will it work? Yes, and so would regular steel, but neither are the best choice to mix with bronze below the waterline, though stainless would be FAR better than steel..

From ABYC H-27

Materials
27.6
27.6.1 All materials shall be galvanically compatible

 

[Hermit Scott]

http://www.pbase.com/mainecruising/replacing_thruhulls courtesy of Maine Sail

I bought flanged seacocks, but this guy on here talked me out of using them. He recommended flange adapters instead. Now I can just unscrew a ball valve, chunk it and replace it without hauling the boat. If you buy a little rubber stopper to put in while you change them, it takes the heart attack phase out of the job, when a small geyser shoots up.
As a matter of fact everytime I go to buy anything he changes my mind. Flange adapters with bronze hardware instead of flanged seacocks, a furler instead of fixing my old one, an LED bow light instead of using cheap LEDs in my existing lights, I bought a manta claw anchor because of his old posts when that was his favorite anchor, I don't wish to spend the money on one of the new generation anchors yet. The best part is he always saves me some money. Thanks again Maine.

 

[redhead78]

I also have the tri flange adapter plate, they call it. I is triangular with a male thread facing up in the boat, the thru hull threads into the bottom fom underside, ball valve on top. then a hose barb. I bought the whle shootin match from Jamestown dist.My hull is a little more than an inch thick, so I am going to epoxy and glass in a piece of 5/8" plywood, inside and use counter sunk 5/16" screws, from outside and nut and lockwasher inside. I guess I should use silicone bronze fasteners if I can find them? Red

 

[sailingdog]

Why would you add a piece of plywood, when you could easily use a solid fiberglass backing plate instead. The plywood may rot and need to be replaced... if you glass in a fiberglass disc, it will not have this issue ever.

I also have the tri flange adapter plate, they call it. I is triangular with a male thread facing up in the boat, the thru hull threads into the bottom fom underside, ball valve on top. then a hose barb. I bought the whle shootin match from Jamestown dist.My hull is a little more than an inch thick, so I am going to epoxy and glass in a piece of 5/8" plywood, inside and use counter sunk 5/16" screws, from outside and nut and lockwasher inside. I guess I should use silicone bronze fasteners if I can find them? Red

 

[Chuckbear]

concerning mixing stainless and bronze, the ball inside of the valve, be it seacock or ball valve is stainless. We use stainless fasteners all the time to install seacocks with no adverse affects. Chuck

 

[Hermit Scott]

I bought silicone bronze hardware from Fastenal, I had to order them though.
I second the fiberglass backing plates. If I can impart one word of advise, buy GOOD hole saws to make them. I had some cheap ones from harbor freight, and it was dull before it got though the first plate. Also I would use a drill press if you have one, and have someone pour water over it while you cut it. The fiberglass dust filled up my whole shop and was nasty.
To make the fiberglass backing plates, I layed out wax paper on an old table, taped it down and used a small roller to start laying down polyester resin. I used 10 oz. and 24 oz. to make the 1/2" thickness, but I think any woven will do fine.
I power sanded the hull inside and dewaxed everything. I used thickened polyester to adhere it to the hull. Explore that link I posted before.

 

[Hermit Scott]

concerning mixing stainless and bronze, the ball inside of the valve, be it seacock or ball valve is stainless. We use stainless fasteners all the time to install seacocks with no adverse affects. Chuck

They are stainless or chromed, but aren't they isolated by the plastic seal? I have a groco strainer. It had a stainless basket inside instead of plastic. There were sizable pits in the bronze strainer body because of the stainless basket.

I don't think the different metals will affect the through hull system that is being installed because the bolts are not submersed in seawater with the bronze. Unless there is any kind of seawater penetration to the head of one of those bolt heads. All you have to do is hit something in the water and it could cause a bolt head to be exposed. I would be concerned more about crevice corrosion. But why use stainless at all? Strength is not an issue, as much as corrosion in a flange.

 

[Chuckbear]

The handles, bolts holding the handles, etc are all stainless and not all isolated. My 30 year old bronze engine strainer has a stainless basket with no signs of pits or electrolysis, I would look elsewhere if that were the case. Groco as well as others ships the strainers from the factory with stainless baskets. My point being to the original posters question about having problem using stainless fasteners, they can be used and are used all of the time. If you don't want to buy a box of bronze fasteners to use a few or they are not available, it is an option.

 

[Hermit Scott]

Groco as well as others ships the strainers from the factory with stainless baskets. .

That is true. I seriously questioned the wisdom behind that choice of theirs when I took apart this strainer I have and saw the pits. I replaced it with plastic.
Why would they have stainless and bronze together in seawater with no zinc? It seems obvious that the bronze is going to be eaten away by the stainless.
Groco is a well respected company, as well I respect your advice Chuck. But I don't understand it.

 

[Chuckbear]

On the galvanic scale, 316 stainless is 53 and bronze is 54, next to each other so the they are not going to have a great deal of galvanic interaction. The entire scale can be found here, http://www.corrosion-doctors.org/Definitions/galvanic-series.htm
Chuck

 

[sailingdog]

Chuck—

I'd point out that passivated 316L stainless is #76 and well could cause a great deal of galvanic interaction. It really depends on what bronze alloy it is and whether the stainless steel is active or passivated. Why risk it??

 

[tommays]

Well

In my now almost lifetime of fixing BIG expensive SS mixers i have seen it all and its on materail carrying certs as to what it is

My favorite is 316 SS anchor pins gettiing eaten by the 316 SS mixing blades they hold in place which is why this is no longer done and everything is now welded and polished to avoide and crevice

53 VS 53-1/2 can in fact lose pretty bad

 

[Ross]

What is necessary here is to establish what the galvanic voltage of each metal is. Gold is the standard for corrosion and magnesium and beryllium are at the bottom of the spectrum. Gold and beryllium in a cell will generate 1.85 volts. Going up the scale gold and copper and lower alloy bronze will generate .35 volts. Stainless steels and gold .50 volts. Therefore the difference between stainless steel and low bronze is .15 volts. That is acceptable.
http://www.corrosion-doctors.org/Definitions/galvanic-series.htm

 

[redhead78]

I just found and ordered, silicone bronze, 5/16" screws, washers and nuts from Jamestown Dist. This co is great if you are rebuilding a boat through the mail.......no tax, and for $36.00 free shipping for a year. UPS will have my package at my house in NJ tomorrow. I agree with you all, thanks for the input......Red