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Hi all fishing chemists... I've got stainless steel rod holders clamped to the aluminium railing on my Quinnie... then secured in place with aluminium rivets.

Which bit... the steel or the aluminium... is a risk from electrolyisis and should I/could I use any kind of zinc sacrificial anode for protection.

Cheers, Slinky

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Ally is at risk as it is lower on the galvanic scale.

Particularly the ally rivots as it is hard to see when they are near failure especially as they don't have much metal in them and a large surface area. You can isolate the rod holders by placing a plasitc barrier ( cheap plastic film like dampcourse that is UV stable) in between the rail and holder next time. You could also when reinstalling use a product called duralac ( huey or boating shops will sell it) which is a liquid barrier in a tube which creates a neutral oxidised chemical barrier layer on the touching faces of both metals. There used to be lots of chromate products like paints , undercoats, etch and barriers but most are now banned for public sale ( due to reaction and chance of heavy metal poisoning) but are still used in aircraft repair / manufacture.

Annodes only work well where there is a electrolite solution ( salt or normal water) in which a current can be caused to flow like on a moored boat hull. Hence the reason you never see annodes on cars etc.

I prefer to use stainless steel rivots with stainelss steel mandrils ( bit you pull to set the rivot that snaps off) as they are more durable. They are a right bugger to drill out when you move stuff though.

Edited by pelican
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Hard to say put a photo up sometime. If your boat is washed off and kept undociover and dry the existing setup will last for years etc but you can't tell the shear strength. A lot depends on gauge of rivot and what ally alloy it is really made of. You might know those answers if you installed them.

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Hi again Pelican,

I used 5/32" aluminium rivets so they'll hang tough for a fair while. I might add it to the winter maintenance 'to do' list and drill them out so I can replace them with stainless.

I bought myself some Duralac for when I do it.

thanks for all the advice.

Cheers, Slinky

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I don't know your boat but if the rails on your boat are painted there is less exposed surface area so possibly less electrolisys or possibility of a problem.

If you redo them I would definately Duralac the rivot and the hole and make sure no swarf from the drilling out is left in the boat. Since you are going to the trouble I would grab a plastic and use it as a physical barrier and then it will never be a possible cause in the future.

Many people say that their fittings aren't the problem when their boats start to get some electrolysis symptoms as the damage is not at the fitting. From experience aircraft mates tell me that it doesn't have to occcur at the fitting and can actually occur because of that fitting at a remote spot which is an easier electrical path - sometimes as metals harden as they are worked, flex , welded or age and that point becomes the suseptable spot for corrosion and electrolysis to work in tandem.


PS Keep duralac off your skin if you want to have kids.

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If it is still the original composition I would keep Duralac off your skin as part of the reason they banned the retail of similar chemicals in sprayable form many years ago was some bad health affects. edit it is a carcinogen Spraying chromates now is only done by aircraft, marine industry as it is the best metal primer for ally but with very strict OH@S as it is poisionous. From memory nervous system problems from contact exposure especially when it was sprayed. Like all chemicals keep em off your skin and don't inhale their vapours.

Copy of description from suppliers page

Used in the Aerospace industry as an essential corrosion inhibiting material wherever dissimilar material are used.

Description Duralac is an anti-corrosive jointing compound for use between joints of dissimilar metals.

Form Duralac Jointing Compound is a yellow paste prepared from an elastic varnish medium of low moisture permeability, a corrosion inhibiting material barium chromate and an inert filler. It conforms to specification D.T.D. 369B.

Properties Barium chromate is only very slightly soluble in water and hence is not leached out of the joint even in the presence of a considerable flow of water. It is however readily decomposed by acids with the liberation of chromic acid so that it is brought into action only in the presence of corrosive influences. It is tough and flexible, absorbs little water and is resilient to seawater. Shelf life is two years from date of despatch. Store below 20°C.

Uses Duralac is indispensable for the sealing of joints between dissimilar metals of all types including magnesium and its alloys. It is also valuable for the protection of metals in contact with wood, synthetic resin compositions, leather, rubber, fabrics etc. When the components of a structure are of different materials, it is essential that the points or faces of contact should be treated with corrosion inhibiting materials because in the presence of electrolytes considerable differences of potential arise, not only where different metals are in contact, but also where components of the same metal under different stresses are in contact: for example as between the aluminium alloy plates or extrusions and rivets or bolts used in building up the structure, in industrial areas where structures are exposed, in flue ducts and acidic vapours. In close proximity to the sea where a salt laden atmosphere will be met with, structures will need the maximum attention to prevent corrosion due to the electrolytic cells set up by the salt laden moisture deposited upon the structure.

Application Duralac is supplied ready for use and must not be thinned. It is best applied by brush. When Duralac is applied to metal or other surfaces the volatile solvent evaporates and the compound sets to the touch, but remains tacky for a considerable period. It is important that the joint should be closed while Duralac is still tacky – so that it is in such a condition that it will flow sufficiently under pressure to close the gaps in the joint. It will harden somewhat if a thin film is left exposed to the atmosphere for a long period and this will prevent the making of a close joint.

Material safety sheet

Safety data for barium chromate


Glossary of terms on this data sheet.

The information on this web page is provided to help you to work safely, but it is intended to be an overview of hazards, not a replacement for a full Material Safety Data Sheet (MSDS). MSDS forms can be downloaded from the web sites of many chemical suppliers.



Synonyms: chromic acid barium salt


Molecular formula: BaCrO4

CAS No: 10294-40-3

EC No:

Physical data

Appearance: yellow powder

Melting point: decomposes

Boiling point:

Vapour density:

Vapour pressure:

Density (g cm-3): 4.5

Flash point:

Explosion limits:

Autoignition temperature:

Water solubility: insoluble


Stable. Oxidizer. May react vigorously with reducing agents.


Harmful if inhaled or swallowed. May be harmful by skin contact. Carcinogen. Chronic exposure may cause cancer, liver and CNS damage.

Toxicity data

(The meaning of any abbreviations which appear in this section is given here.)

Risk phrases

(The meaning of any risk phrases which appear in this section is given here.)

R20 R22 R45.

Transport information

Personal protection

Safety glasses, gloves, good ventilation. Handle as a carcinogen. Take care to avoid inhalation of dust.

Safety phrases

(The meaning of any safety phrases which appear in this section is given here.)




Edited by pelican
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