Blakes seacock replacement

My Swan 40 is 37 years old and I believe the seacocks are original.  The heads outlet seacock has been dribbling now and again so last winter I had it lapped in with very fine grinding paste.   The first few months it was perfect but now it is leaking again - but only when it is in the closed position, when it's open there is practically no leak.   The other Blakes seacocks work fine and 100% dry.   

 My questions are: at what stage should I consider fitting a new seacock and which make ?  (this is not an easy job as the skin fitting is glassed into the hull)      Are there any other ways to stop the old seacock leaking?

Many thanks

Richard Forrest

Hi Richard,
Blakes seacocks can last for a very long time so 37 years is not surprising.
They need replacing usually when the surface of the rotating cone gets too deeply pitted and becomes dangerously thin. Till then the best way to treat them is lapping with grinding paste: first coarse and then thinner. In this way small pitting or ellipticity is corrected and perfect sealing is restored.
If you browse the "maintenance/manuals" section in this site you will find a useful article on the subject (thanks to Matteo...). From what you write you probably just need a bit more lapping but be sure to check well the thickness of the cone wall.
Replacing the seacocks is not a terrible job; I would say the the worst part comes from their recessed position. Another useful article on the subject in this site (what would we do without Matteo ...).
Regarding what brand of new seacocks, we could start an infinite discussion as you can easily find in many nautical sites. I have your same problem and I already bought the same brand but I understand that they are made of a different alloy and I ignore if this is good or bad news.

Daniel, 411/004

Dear Richard, I replaced all my seacocks on Fandango. I initially had the Blakes replacements (pricey), but when I took the old ones out and I noticed how bad they were from electrolisys, I changed my mind and instead of the Blakes I installed the ones from Forespar made out of marelon. Check them out, they are very reliable, in fact, according to Forespar, they are now standard on the new Swans (Did not check on this). They can also be recessed into the hull and some have the capability of taking two hoses at a low profile, in case you don't want to open any more holes on you boat and you want to add a water maker.

To give you an idea on how bad the old ones were, when I pried the one from the galley sink, it easily broke and it was all pink inside (corrosion indicator).

Rodrigo

Dear all

It appears Forespar is not well informed, the smaller performance Swans use their Flowtech model because of its flush-closing properties. This is not the same model as shown in the picture above. The bigger Swans use bronze seacocks.

The pink colour Rodrigo reports indicates that the material is brass and not bronze, and therefore corrodes away. The problem is that brass is often sold as bronze, and there is no way to tell from the appearance what it is. Then there is also something called inhibited brass, which does not corrode provided it has the correct composition, quite confusing.

Brass can be used in fresh water, for example is fine for plumbing in houses, but do not use such valves on yachts in salt water.

Chemical analysis or salt bath testing would be needed in order to know, hardly within the ordinary yacht owners possiblities. The reliability of the supplier is at premium.

Kind regards

Lars

Dear all,

I think that the blake seacock are made of brass covered with bronze (or is it copper?)  Once there are warned out the brass is in contact with see water and the corrosion comes in.  I have maintained mines (swan 47 n°59) (see picture) and we can see that there is still bronze on the top but there is no more where the hole is.  Not all of the 7 seacocks are like that and some are perfectly clean and beautifull.  I will therefore try to buy new one but without changing the part fixed on the hull.  Do you think I can still find these spare parts?  When do you think you must change the whole seacock?

Ludovic of Rumtrader

Dear Ludovic,

the Blakes are made of a high specification DZR (dezincification resistant) brass, and my suggestion is NEVER mix different parts. If you buy a new one change the cone and the fixed to the hull base. This is not a big job as one could think. In the "maintenance" section of classicswan.org website there is an article wich explains very well how to maintain and overhaul your Blakes seacock.

Fair wind!

Matteo (38/067 Only You)

Ludovic,
in addition to fully endorsing what Matteo writes, I like to clarify that the original Blakes seacocks are not "brass covered with whatsoever" but are made of solid marine grade bronze. If you scratch the discolored corroded surface you will find only bronze.
There can be different reasons for the corrosion you find but I bet that very few seacocks working in salty water would be still in such fair condition after 30 years.
Lately Blakes switched to using a different alloy (DZR) which, apparently and hopefully, is even better.

I have another peculiar question: does anybody know why Nigel Warren in his book "Metal corrosion in boats" writes strongly against seacocks that sound very much like the Blakes although he never names them?
It seems almost a personal matter.

Daniel, 411-004

Mateo and Danielefua,

From your input I understand that my seacocks are in plain bronze. I will of course do my best to keep this original equipement and have gret pleasure in discovering the quality of each of the parts of our beloved S&S 47.

Thank you for this great internet site that is of great help to me.

Ludovic of Rumtrader

Ludovic

In your picture it looks like the cone has deformed so the middle part is concave, and does not touch the body when inside it. If this is so it could be tried to expand the middle part so the cone becomes straight.

If there is too little thickness left, or the body has expanded through corrosion in the middle part this will not work.

Daniel

Nigel Warren indeed refers rather critically to taper plug type seacocks in his book. My guess is that part of his comments are caused by the sales information put together by chandlers. Also these seacocks are made in the UK and he probably has seen a great number of them, and some have had problems.

Lars 

Dear Professor,

There is a part of the cone that is in contact with the water inside the boat when closed. I believe this is why we have corrosion there.  My plan is to change the cone and to grind the tube with the new cone.  I have asked for this cone only but have not had any response from the distributor yet. 

Is this a bad idea?

Thank for you help

Ludovic from Rumtrader

I am sorry Ludovic but everyone will confirm (as Matteo already did) that it is not a good idea. There are at least three reasons:
1) the angles of the cones may be not the same and trying to match them by simply lapping may take ages.
2) the metals may be not compatible for galvanic reasons.
3) if the inner cone has changed alloy structure for age, so probably did the outer.
In particular you will find that the manufacturer does not sell separate parts for the above reasons. You will be able to buy only whole seacocks and everybody will discourage using one part of the assembly discarding the other.
Sorry but this is it!

Daniel, 411-004

Thank you for all your advices.  We changed one seacock by original blake seacock.  I was surprised to see that the orginal fitting was just with polyester and not with bolts.  After some discussion we decided, for the new seacock, to use the bolts that are proposed by Blake.  This changes the outside apearence and was quite a lot of work as we repaired the polyester first. 

For the next replacement we have not decided yet how to fit it: with bolt or with polyester?

Any advice?

Ludovic

Ludovic,
this is a very good question I would like to hear comments about. As you write, Nautors fixed the sea-cocks from the inside with a patch of fiberglass as explained in a document that can be found in this site while Blakes recommend the way you adopted. Are the two procedures equally safe? Is anyone informed of what the Lloyds recommend?

Daniel, 411-004

I asked advice from a surveyor I trust and he confirmed that it would be good practice to "fit the skin fittings/valves with the external fitting as per Blakes instructions".
After this, unless somebody convinces me differently, I think I will follow his advice and do as Ludovic did every time I substitute a Blakes thruhull/seacock.
Just one more thing: if the hull is not at least 1" thick, it is advisable to fit also a properly made backplate - in glassed plywood or, even better, in fiberglass.

Daniel, 411-004

Daniel,

We did put first fiberglass to fill the gap left by the ring of the old seacock and then did a hole again so that the thickness of the hull was leveled.  We also then covered with gelcoat (see pictures)

I also ordered the special the seacock grease from Blake (a green stuff).  The previous owner of our boat had showed me the maintenance with simple marine grease.  The difference between the blake product and a simple grease is incredible.  (En français: il y a pas photo!) 

Another issue is that the new seacock have a grease valve enabling to add grease while in the water.  This is a major improvement but I do not have (yet) any idea of the normal grease injection rythm (once a month?)

Ludovic,   47 Rumtrader