Folkboat stainless through hulls/plumbing

Hi everyone,

A few questions

I have decided to install a kiwi prop (stainless steel & plastic), given that there is no silicone bronze components, I was considering stainless through hulls as I thought this would reduce the risk of electrolysis, though I suspect the rudder pintels & gudgeons may be silicon bronze (I recall reading that stainless through hulls are a bad idea, but can't remember the context) or should I stick with silicone bronze.

location on of the cockpit drain through hulls (I need to install new ones as they use to be where the prop cutout now is) I was considering mounting these in the transom so that I can inspect them a lot easier (in the Lazerette locker). Is it worth putting ball valves on these?

I was also considering plumbing the sink drain to the cockpit drain to reduce the number of through hulls (probably a 3.5m hose run, bottom of sink is above the cockpit floor). Has anyone done something similar?

www.trudesign.nz/marine/products/20-skin-fittings-threaded

Better than stainless and probably cheaper too.

stainless is all pretty cheap Chinese there days.
Go for these www.deckhardware.com.au/plumbing/thru-hull-connectors/full-threaded-flush-head-thru-hull-connector/
(Other types on the website.)

Thanks for all the replies guys,

The pitting of submerged stainless is what I had heard about, I have silicone bronze through hulls all ready, so will stick them in. I am not too keen on plastic below the waterline.

with the Galley plumbing, the sink cutout is there already so I will plumb in the drain, does anybody sees problem with connecting it to the cockpit drain?

Any thoughts in routing the cockpit drain to the transom (only considering this so that I can easily access them for inspection etc?

Thanks

Geoff

Keep all runs as short as possible and on a constant downward gradient or they are going to stink.
From my own experience.

Probably overthinking things again, I think the potential problems I would create would mitigate any advantage

Select to expand quote

David88 said..

andy59 said..

David88 said..
Stainless needs to be exposed to air to not deteriorate. It is not suitable for under water skin fittings. That is why if your stainless keel bolts are under salt water forever eventually they will get pitted and probably break.

Sorry for the thread hijack but could you explain that further David eg
does the stainless need to be dry for periods to develop a "skin"?

Sorry Andy i'm not sure why but I do know Stainless is susceptible to crevice corrosion & pitting if it's underwater or closed off e.g in a swagged fitting at the end of rigging wire.

There is normally sufficient oxygen in water to create a chromium oxide surface on the steel. That forms a passive skin layer which protects the metal from further oxidation. This layer is always under attack from the hostile environment its in and oxygen in the environment continually replenishes the protective layer ...However, once the water surrounding the stainless becomes a stagnant low oxygen environment, any acids or corrosive salts in that stagnant solution will continue to attack the passive chromium oxide layer which isn't going to be replenished due to the lack of oxygen in the stagnant solution and the result is the metal starts to get eaten away.
Aluminum does a similar thing.