The AMPHS World - seacocks and thruhulls

Seacocks and thruhulls are parts of the boat which should be attached special attention. Everyone knows : advanced electrolysis, improper assembly, unsteady sealing can turn the boat into a pool, or even offer him a oneway ticket to the depths of the ocean ; apart from setting up a cone in the thruhull and pump, there is not much to do when you are far from a coast.

On the Amphitrite, there are 3 valves and thruhulls in each bathroom, one for emptying the kitchen sink, one for the admission of sea water, 2 or 3 for the engine, 2 or 3 for the pumps, and 2 for the log and sounder, and if there is a watermaker, generator, air conditioning or cooling unit with heat exchanger, much more. In total, this makes a lot of potential water inflows, it is imperative to monitor.

A seacock (= ball valve) must be replaced when it becomes hard to turn. For the thruhull is another thing. Here's what David MERLOT, former head of manufacturing at Wauquiez, to whom I spoke before operating :

My advise is to keep the thruhulls. Why?

The material is sinter bronze, quality of alternator bearings ; in addition, it has a thickness of 5 mm and is included in the polyester (knurled diagonally).

The thruhull was positioned in the mold immediately after casting the gelcoat and the hull was built around (thickness of 5 cm) ; by the withdrawal of the polyester material, it was blocked (see photo).

On the other hand, this mounting avoided to wear holes in the hull which kept all its seal ; but the thruhulls must be checked after taking down the seacock if there is no electrolysis ; to unscrew it no problem, no jamming ; the bronze must have a beautiful yellow color. Outside, when sanding, you can also judge the state of the thruhull (thickness and color).

You can screw directly into a seacock of stainless steel without corrosion problems. The nut is there to block the valve in a good position. Mounting with Teflon tape, you must be generous by turning, even better : screw and unscrew and set tape again.

Note : These tips are given only for thruhulls of origin, not those that were added during the installation of new equipments.

As I replaced five seacocks (toilet and lavatories) and as, the last I saw her, my boat was still floating, I might add that:

   1. In the bow bathroom a valve resisted the dissambling ; i had to cut it away. In fact, it was a very difficult access and it was not possible to use a large tool.
   2. After 28 years, the thruhulls show a beautiful yellow, no trace of electrolysis.
   3. Between thruhull and seacock, I used Loctite 577, a product for sealing connection ; given the tightening of the 3 valves in a small space, it is not easy to apply sealing tape, but for pipe-to-hose adapters I used Teflon.
      65.213.72.112/tds5/docs/577-FR.PDF
   4. The dimensions of the valves (in inches) are : 1˝1/4 (toilet drain and sink), 3/4˝ (water inlet) ; adapters (of varying diameter) do not always stick with pipes, because, currently, it is used most often 1˝1/2. In Tunisia, it's simple : you let turn the parts you need.
   5. In the aft bathroom rear (original !), the sink is not above the thru-hull : I got out of the valve with an elbow adapter.
   6. I used both 316 stainless steel seacocks and brass seacocks to compare the lifetime of the 2 valve types.

      See also: www.amphs.org / thread.php

      Bronze or brass? Brass is an alloy of copper and zinc ; the zinc lost by electrolysis ; it's why that the brass components become reddish, which is the color of copper ; in this case, there is danger. In addition, it should be noted the marked and rapid corrosion of brass in presence of ammonia (remind you of the screws holding the toilet at home that are not resistant to cleaning products).
      Bronze is an alloy of copper and tin ; tin resists better than the zinc electrolytic phenomenon and makes this alloy more stable for use in shipbuilding. Sinter bronze is still more stable. When electrolytic is appearing, copper prevails on the tin and the alloy becomes pink.

      NB : The photos below taken with a GSM without flash are not very good.

2010.05.08 - remplacement vannes (01).jpg
We can see the thruhulls, after taking down the seacocks, with tightening nuts. The inferior part is wrapped in polyester.

The seacocks deserved to be changed.

On the left : new stainless steel seacock for sink. In the middle : new stainless steel seacock for the WC inlet. On the right : hose adapter turned in Tunisia (15 E).

Article written by Mindelo