Testing Skin Fittings

[andf]

My new to me boat (ten years old) is out of the water at the moment and I would like to check the state of the skin fittings and seacocks before it goes back into the wet stuff.

Apart from the obvious, like makeing sure all seacocks open and close etc. is there a way they can be checked more thouroughly.

I would like to check for de-zincification (is there such a word?) corrosion, cracks etc. Anybody got any ideas or top tips?

Courier (used to be Crianza)

 

[vyv_cox]

Seacocks and skin fittings made from any of the modifies brasses, such as Admiralty bronze, naval brass, etc., can suffer dezincification. Brass is an alloy of copper and zinc, so when the zinc is lost to corrosion the copper remains, making the allow look pink. You need to polish the surface of the metal with wet and dry paper until it is as new. Any pink will then be quite visible.

However, a bit of dezincification on the surface of a skin fitting should not cause much concern, it's only at critical points, such as the internal radius of the flange-to-shank junction, that failure might take place. This isn't a very easy area to inspect and taking all your fittings off to examine them would be a major task. I would clean them up a bit in-situ, then give them a thorough visual examination, checking for big pits, cracks etc. Only if you find anything unpleasant would I go any further.

 

[Norman_E]

Good advice, to which I would add (from an expensive experience) that if the skin fitting has a screwed on ball valve especially one that is chrome plated, treat the ball valve with great suspicion. I had one which looked OK externally break in half just above the ball when I tried to close it. These ball valves are mostly made for domestic use, from common brass and are made in pretty thin section to save money.
Question is, what to replace them with? Are there any good quality valves around, made from glass filled plastic?

 

[VicS]

What Vyv Cox says is correct BUT the difficulty will be knowing if any pinkness you see is just on the surface or whether the dezincification goes deeper. In any case the parts that are exposed to sea water are the flange on the outside and the <u>inside</u> of the fitting. Obviously you can look at the flange easily but the insides of the fitting will be rather more difficult.

Sorry as criticism goes that's not very constructive!

Someone is thinking of suggesting you whack 'em with a hammer. If they break then they are dezincified. The trouble with that is that the whack may be the last but one straw. The last one being somebody oening a valve a bit awkwardly when you are back afloat!

Hopefully your fittings are either a genuine tin bronze or at the very least a dezincification resistant (DZR) brass.

If you do spot any evidence of significant dezincification the question will be what to do about it.

Replace any suspect fitting(s) with bronze or DZR may be the best long term solution but also the most expensive. Cathodic protection may be a less expensive alternative. Remember, though, that anodes must be connected to, and fairly close to, the items they are to protect and also that non ferrous fittings should not be connected to the same anodes as other, ferrous, items.

 

[pyrojames]

Hit them witha hammer! /forums/images/graemlins/smile.gif There are two reasons for doing this. 1) they might break in which case replace them. 2) Listen to them when you hit them, they should "ring". It's easier to do with a prop, but a dezincified piece of brass/bronze will go thud, where as a good piece should ring, bell like.

 

[andf]

One thought ocurrs to me when reading the collected wisdom so far:

If I pulled out one of the smaller fittings and did some distructive testing on it - like cutting it in half and having a good look, would it be safe to assume that all other fittings would be in the same state?

 

[damo]

If they all had identical solutions passing through them, and they were all identical composition, and they were all subject to identical galvanic pressures, and they were all fitted exactly the same way, and they all had the same amount of use etc etc....

It isn't something I would rely on /forums/images/graemlins/smile.gif

 

[ebbtide]

"Cathodic protection may be a less expensive alternative"

M G Duff, the acknowledged experts, specifically warn against wiring up skin fittings. Anyone care to expand on that? Mine are certainly linked: prop shaft- engine-external anode on the quarter. How about WC fittings? What is the significance of 'line of sight'? Or the usefulness of hanging an anode over the side?

 

[vyv_cox]

only guessing really, but if you have slight compositional differences between the skin fittings, one will inevitably be more electronegative than the other. Left alone they will probably sit in seawater quite happily, but linked together there is a risk that one will corrode preferentially while protecting the other.

On the original question, as far as I know all the fittings on my 23 year old boat are original. The Blakes toilet fittings are probably bronze but the others could be anything. The boat has spent the majority of its life afloat, only about 6 or 7 winters ashore. No sign of severe corrosion that I can see.

 

[VicS]

[ QUOTE ]
specifically warn against wiring up skin fittings

[/ QUOTE ] I cant find that on their website.(but please point me to it) They do however say, "Do not bond the same anode to ferrous and non-ferrous metals". A point I had already made. [ QUOTE ]
How about WC fittings

[/ QUOTE ] I take it you mean the skin fittings. They should be bronze, preferably, or DZR brass neither of which should need cathodic protection in normal situations. [ QUOTE ]
What is the significance of 'line of sight'?

[/ QUOTE ] Perhaps not to be taken too literally. The anode must not be totally shielded from what it is to protect by say a keel but the slight curvature of the hull between the two should not be a problem. Steel rudders or keels should have an anode on both sides. [ QUOTE ]
Or the usefulness of hanging an anode over the side?

[/ QUOTE ] It can be useful but it has to be hanging fairly close to the item(s) requiring protection and there must be a good low resistance electrical connection between the two.

 

[dickh]

You can get quality bronze ball valves but you will have to get them from a specialist supplier and specify bronze - the normal ones in the chandlery are only nickel plated brass - the proper bronze ones cost about 3 to 4 times the brass ones. I believe ASAP supplies can supply the bronze ball valves.

 

[Norman_E]

Noted, the reason I am curious about getting good glass filled plastic ones is that my boat is in Turkey, where I can only find the plated brass ones, and bronze ones are heavy to carry out. I also think that good plastic ones may actually be a good long term solution.

 

[Tranona]

Yes, you can get plastic through hulls. usually fitted to steel boats where there is an obvious potential galvanic problem. However, for a GRP boat there is no need for this. Bronze through hulls are best but many boats have lower quality "brass" fittings as described in other posts. The most important thing is never to use gate valves below water, only ball valves with a 90 degree handle. Most handles are regrettably steel so often rust in the damp bilge, but the valve still works. Great advantage of ball valves is that they are held in the hull by the locking ring rather than bolts. However, if you really want to feel secure, replace the whole lot with proper Blakes seacocks. I had to replace the toilet outlet last year and a 1 1/2 inch Blakes was only about £10 more than a Bronze ball valve and fittings - but twice the price of "brass". However it will outlast me!

 

[vyv_cox]

<<< the normal ones in the chandlery are only nickel plated brass >>>

There have been two of these much-maligned ball valves, on my engine suction and galley sinks discharge, since before I bought my boat some 12 years ago. I look at them from time to time to check for problems and have found none. They work perfectly well although, as has been said, the handles tend to rust. Seems to me they have lasted a lot longer than some of the expensive 'proper' stuff on my boat, in a worse environment.