electroylsis and aluminum tanks

[Dan_W]

HI,
I was hoping for feedback on electroylsis. I'm putting new tanks in our old Monk cruiser. I've sold the boat and part of the agreement is a new set of aluminum tanks to replace the 5o year old steel tanks. The question is, should the new tanks be grounded to the transom zinc or not. The tanks are under the aft deck and rest on wood deck frame and have no connections to anything electrical on the rest of the boat. My first impulse is to go ahead and attach the tanks to the zinc but I'm not sure.
Thanks for any help.
Dan

[cbob]

Dan, It would seem that unless you are using rubber fuel lines (diesel or gasoline?) not recommended or legal, the tanks will be electricaly connected to the engine(s)with, I assume copper tubing, and then to whatever the engines(s) are are electrically connected. Is the boats metal electrically bonded?? To what are the zincs connected?? Need more info. Were the iron tanks connected (grounded) by the exesting service metal? fuel lines, if so you are home free. cbob

[mmd]

Here's how I'd build and install them:

Build the tank so that no moisture can lay on the tank; i.e., the top must be flat (even a bit convex is good) and there are no indents for fittings or clearance. Place a neoprene or synthetic rubber pad between the mounting feet/lugs to insulate the tank from moisture and acids in the wood structure. If securing straps are used, they must be able to drain away any moisture, and I prefer to mount them with a neoprene pad between the strap and the tank surface. Use Type 316 stainless steel fastenings to secure the tank to the hull structure. Weld a small tab in an out-of-the-way place so that you can attach a small (14 guage minimum) ground wire to a ground plate to dissapate static electricity that builds up while filling. Attach a ground wire to the deckfitting, too. Use Type 316 hose fittings and valves on the tank. Plumb the system using high-quality reinforced flexible fuel line - such as Trident - that meets USCG, ABYC, ISO, and SAE J1527 specs and remember to use two heavy-duty all-stainless hose clamps at each fitting.

(Edit to add "synthetic rubber")

[ 12-18-2004, 08:40 AM: Message edited by: mmd ]

[Dave Fleming]

I agree fully with MMD's recommendations and add one word of caution.
I would not put copper any where near an Aluminum tank.

[TER]

Just for reference I thought I would point out that a galvanic series like this one www.dixdesign.com/galvanic.htm (http://www.dixdesign.com/galvanic.htm) can be used to determine which metal will corrrode if two metals are electrically connected. The more anodic metal will corrode. In this case it seems that zinc is more anodic than most aluminum alloys so it would provide protection against corrosion of the tanks.

Tom

[mmd]

Tom, you are absolutely right if the aluminum tank is in contact with a dissimilar metal either by direct contact or via a conductive medium such as seawater. However, in the situation of an aluminum tank in a (presumably dry) wooden boat interior, there is no normal situation wherein the tank regularly comes in contact with dissimilar metals, so by isolating the tank from all electically conductive materials as I have described, there is no need to connect the tank to an exterior zinc anode.

[TER]

mmd, thanks for clarifying. I didn't mean to cause any confusion or question your method, I just thought that must have been the reason the original steel tanks were connected to the zinc. Sorry if my post caused any confusion.

Tom

Edited: P.S. I had just taken my final exam in materials class this morning. Corrosion and corrosion prevention were covered in it so I guess I just had corrosion on my mind.

[ 12-17-2004, 09:36 PM: Message edited by: TER ]

[kc8pql]

Originally posted by mmd:
Use Type 316 hose fittings and valves on the tank. Which brings up a question. Anyone know where to find 316 tank fittings, or better yet, alu.? My aluminum tanks are installed as mmd describes above but I couldn't find the SS fittings I needed so I used brass and teflon tape in an effort to isolate them. Been bothering me ever since. I'd really like to change them out.

Ken

[Ross M]

"or better yet, alu.?"

Earl's Performance Plumbing (http://www.holley.com/HiOctn/ProdLine/Products/EPP/EPPA/Alum.html)

:cool:

[Dan_W]

Thank you everyone for the response. The original tanks were not grounded to the zinc. They were attached to the engine fuel system via USCG approved rubber fuel line. The installation plan I had was to set the tanks on the existing deck beams that the old tanks sat on with some added stringers to support the bottoms better. I was going to set them on rubber. The new deck framing will hold the tanks in place. I had planned on using copper tubing and valves up to the bulkhead just ahead of the tanks and then using rubber hose again to make the connections to the fuel/water seperator mounted there. The top of the tank just has a 1/2" pipe thread fitting. I was going to build a fuel pick up tube out of copper to go in that hole. Bad idea???? Thanks again for the input, it is much appreciated.
Dan

[RonW]

http://marinesurvey.com/yacht/fueltank.htm

Some more usefull info. on aluminum tanks.

[mmd]

Ken, I strongly advise you to replace the brass fittings in your tanks right away. Teflon tape will not insulate the two dissimilar metals from each other.

A quick google came up with Harrison Piping Supply (http://www.harrisonco.com/Valves.htm) in Michigan, Marwin Valve (http://www.marwinvalve.com/productline.html) in Cincinnati, Robeck Fluid Power (http://www.robeckfluidpower.com/prod-serv.html) in Aurora.

Open google and type in "stainless ball valve Ohio" and you'll get quite a list of places to check out, or use the ThomasNet (http://www.thomasnet.com/home.html?navsec=header) industrial search engine to find distributers in your area.

EDIT TO ADD: Dan, yes, bad idea. The only materials that should touch the aluminum tanks are stainless steel, plastic, and more aluminum.

[ 12-18-2004, 01:53 PM: Message edited by: mmd ]

[Dan_W]

O.K. no copper/alum mixing. What about coming off the tank with a stainless hose fitting and a piece of rubber hose to connect to the rest of the fuel system. I don't know if my budget can afford going all stainless!
Thanks again for all the great advise and resources.
Dan

[Dave Fleming]

Not just rubber hose but an approved fuel line.
Cummins sells it by the foot. Whomever is making the tank for you should have a handle on that stuff, especially in the Seattle area.

[mmd]

Dan, just the fittings that contact the tank need to be stainless as long as you use approved fuel hose. This means a stainless steel nipple at fill, return (if req'd), and vent, and a stainless ball valve at the supply outlet. Such hardware for two tanks should be able to be had for about $100.

[trull]

For static reduction, I might add that to keep copper grounding wire from aluminum grounding tab you can use those Al/Cu crimp terminals that electricians use. Available at your local electrical supply.