pic 3 Ollie grinding

8th January 2021

Deacons

Seacock Replacement

Boatcare briefing
Seacock replacement is a job we specialise in at Deacons Marina. A seacock is simply a valve that fits on to a thru-hull skin fitting. The seacock's purpose is to allow water to pass in or out of the boat through the hull to inboard equipment and to provide a positive shut off from water ingress if required e.g sea water used for cooling the engine and to flush toilets.
 
Seacocks should be exercised regularly; ideally once a month, checked annually, and replaced as required. If you do not move metallic seacocks regularly, they can seize, preventing you from shutting them off in an emergency.
 
Traditional seacocks are metallic - brass or bronze. Over time these will start to leak due to chemical erosion and de-zincification, especially of toilet and sink seacocks – this erosion results in pitting of the ball valve resulting in a poor seal and water ingress even when closed. De-zincification can also cause them to become brittle, increasing the risk of failure.
 
Below, a picture showing dezincification of a DZR brass seacock. This is essentially corrosion. The expected life of most DZR fittings used below the can be as little as 5 years, which is all that is required to meet the requirements of the Recreational Craft Directive which is the standard that all leisure boats are built to in Europe.
PIC 1   A pic showing de zincification (corrosion, coloured pink)
 
 For this reason, we replace metallic seacocks with Tru-Design seacocks - the first composite through hull fittings to be certified by the Int. Marine Certification Institute (IMCI) Belgium. Designed and made in New Zealand, the Skin Fitting body and nut are moulded from glass fibre reinforced nylon composite. High strength, high-modulus glass fibres provide dramatic strength, stiffness, toughness and dimensional stability and does not corrode.
 
 
pic 2   lots of seacocks new and old

Our process for seacock replacement is as follows;
 
First we go inside the boat and remove the pipe (be that to the toilet, sink, or engine) from the hose tail of the seacock. Next we grind off the skin fitting on the outside of the hull, taking care not to scorch the hull. This leaves the area prepared for the new skin fitting.

We insert the new skin fitting, placing Sabatack around it first - (this is a moisture curing polyeurathane sealant and adhesive) – behind the flange.
 

Next we go inside the boat, and place Sabatack sealant/adhesive on the locking nut to secure the skin fitting in place in the hull. Then follows the seacock itself – this is threaded on to the skin fitting again with Sabatack applied.

Finally, the hosetail is threaded on to the seacock – leaving it ready to secure new pipework to the tail.

Pipework is secured to the seacock with two hose clips and then attached to the inboard equipment be that sink, toilet or engine.
 
Finally, we make good the hull, reapplying primer and antifoul to the area.
 
Tru-Design will not corrode. We would still advise that they are exercised regularly to check they are moving freely when you need them.
 
If you would like us to inspect or replace your seacocks, please just contact our boatcare team at 02380 402253. 

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