Refurbish or replace: Seacocks?

There are a couple of boat items that our Rival 38 has in abundance. Windows and Seacocks. Both are really important as means of blocking holes in the boat and so very helpful in staying on top of the water and not under it. Most of us are pretty familiar with what a window is 🙂 So, I’ll start with the seacocks.


Boats need holes that are below the waterline and so normally submerged. These are used both for seawater coming in (to cool the engine, or as water to flush a toilet for example) and for water (and other “stuff”) going out such as sink drains and toilet flush (there are also ones that have a paddlewheel poking into the water, these are to measure speed, faster the paddlewheel turns the faster you are moving). There are typically two key parts, the “through hull” and the “seacock”. The through hull is, unsurprisingly, the part that goes through the hull, the skin of the boat. Modern ones tend to have a “mushroom” big flange on the outside and then the pipe coming inside is threaded so big nut clamps it to the hull tight enough (with sealant) to stop water leaking in. Older ones (typically made by Blakes) have four bolts around the outside of the main hole that provide the clamping.

Technically the “seacock” is a valve attached to the through hull. These are used to block the hole in the boat when they are turned off. If they are turned off it doesn’t matter if a hose fails or falls off, you won’t sink.

Vida has loads of seacocks below the waterline. From front to back:

  • 3 for the Forward head (basin, toilet in and out)
  • speed impeller (the paddlewheel)
  • galley sink drain and salt water inlet (used to wash up with salt water)
  • engine cooling intake
  • 2 times cockpit drains (so if a wave comes over the boat and fills where you sit then the water will drain out)
  • 3 for the Aft head (basin, toilet in and out)

Other holes without proper seacocks

Plus there are some holes that are “normally” above the waterline (but that can change if you are heeled or if you had a leak somewhere else that started to fill you up):

  • One manual bilge pump
  • Engine exhaust (water cooling)
  • 4 deck drains (draining the deck down a pipe to the waterline to avoid water staining the side of the boat)
  • gas bottle locker (propane gas is heavier than air, this makes sure a leak doesn’t collect in the locker and cause an explosion)


Finally, well above the water but susceptible to spray and rain:

  • 3 fuel tank air vents (not sure why as we only have 2 fuel tanks)
  • 1 fan air vent for battery compartment and engine (fan isn’t actually wired in and new batteries don’t vent gas)
  • 1 vent for hot air heater exhaust (heater removed due to dangerous rust and we didn’t want a 4th type of fossil fuel (diesel main engine, propane cooking, petrol dinghy engine, paraffin heater)
  • Fridge compressor (we have removed it as rusty and didn’t work)

Plus we have a variety of air vent’s and opening hatches for the living accommodation but that is a separate story.

Their condition

All but one of the seacocks below the waterline are original Blakes models and they are old enough to be made from Bronze (which is the best metal for them). One is newer (engine cooling water intake), installed when the engine was replaced 6 years ago.

All the Blakes ones have been carefully greased and all the handles turn properly. The surveyor checked them all and passed them all.

The newer seacock failed. It seems it is made of DZR Brass “DeZincification Resistant brass”. Brass is made from copper and zinc. If there are electrical currents in water then electrolysis removes the zinc and the seacock becomes weak and can easily fail. We have no choice but to replace this.

However, another Rival boat owner found that his Blakes seacocks passed the surveyor test but when he removed the bolts he found they were very weak in the middle of their length. This is worrying. The challenge is that “real” bronze replacement bolts are very expensive. So people are replacing them with stainless steel (potential electrolysis due to different metals) or silicon bronze. Another option is to replace them with composite fittings (not nylon but much more sophisticated to be stronger and better able to withstand both heat and cold).

So what do we do?

The Sustainable challenge is quite tricky when it comes to seacocks. Obviously from an environmental impact it is much better to refurbish. However, problems with seacocks are the number one reason for boats to sink (at least while in harbour). Sinking your boat is definitely not “Sustainable” 🙂

So we are not going to apply a “one size fits all approach”.

Below the waterline:

  • We are going to remove and fill 4 seacocks by switching to composting toilets (nicer to use, they don’t pollute the sea and we have 4 fewer holes in the boat to potentially sink us).
  • Engine water inlet. We are going to replace this with a composite seacock from TruDesign which seem to be widely recognised as the best composite ones.
  • Galley salt water intake. Remove and use for a fridge cooling plate. Long term we will have a watermaker so won’t need to ration fresh water as much. Sadly coastal sea water is unlikely to be clean enough to want to wash-up in it.
  • Speed impeller. Remove and fill. Instrument is well past it’s sell by date. Impellers are unreliable and frequently get blocked by weed and barnacles anyway. Will rely on multiple GPS devices to give speed over ground. Amazingly our boat has a very, very old fashioned Walker log as well (where you tow a little propeller on a line the mechanical action of the spinning line is turned into a speed display). We hope to make a fortune selling this 🙂
  • 3 sink/basin seacocks. Still thinking about what to do about these: Nothing/Replace Bolts/Replace with Composite/Relocate above the waterline/Have long hoses and combine into a single seacock.
  • 2 Cockpit drains. Still thinking about what to do about these: Nothing/Replace Bolts/Replace with Composite

Above the waterline:

  • Engine exhaust. Looks good, has a high “anti siphon” hose.
  • Bilge pump. Very unhappy with the location of this. It has an inaccessible gate valve which the previous owner didn’t know about. Want to fit an additional automatic electric pump and have a much higher discharge point.
  • Deck drains. Still haven’t found these (very hidden behind fuel tanks etc) but so far have heard of no problems with them.
  • gas bottle locker. We are not going to have gas so we will be able to fill this in.


  • Fuel tanks. Check and do maintenance.
  • Engine/battery cooling still thinking about this (not needed for Lithium Phosphate batteries and potentially only needed in the tropics for the engine)
  • hot air heating exhaust. re-purpose for aft composting toilet vent
  • fridge compressor. Goes into the cockpit rather than outside. Not an immediate concern


Hopefully we can cut down from 12 seacocks to 4 (or 6 if we keep them for the head basins) with the expectation of adding 1 more in the future for a watermaker (but in the very long term maybe losing one if we can switch to an electric motor).

When it comes to the above the waterline holes the biggest change is going to be to the bilge pumps which is actually one of the biggest risks at the moment (will be submerged often when sailing and due to being inaccessible has never been serviced or closed).

I know this has been very long winded. It has taken us weeks to understand and think about what to do. Hopefully the outcome will not only be safe but as sustainable (in every sense) as possible.

6 thoughts on “Refurbish or replace: Seacocks?

  1. David Hembrow September 19, 2019 / 7:31 pm

    I know nothing about boats. Still, this is interesting reading. Issues I’d never heard of being addressed. It’s great that you’re converting the boat to have a far lower impact.


    • dave42w September 19, 2019 / 8:02 pm

      Thanks. As we don’t have much control over the impact on our home (because it is provided and maintained by the Church for us), so it is good to be able to get on with implementing our values.


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