Cooling raw water intake.

[tom52]

Advice please.

My saildrive leg is also the intake for my raw water for engine cooling. The flow seems to be increasingly restricted, and keeping it clear of mussel colonies etc is a losing battle.
So........
I thought I would bypass the whole thing with a new intake. However I would prefer not to put another hole in the hull.
The sea water intake for my heads is also conveniently placed for engine cooling.
The ASAP catalogue features a double outlet Y ball valve. Using such a fitting could I use the existing heads inlet for both purposes? Or is this solution too good to be true because there is some law of flow mechanics hydraulics or plumbing that makes this a daft idea.

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[Talbot]

Will the existing through deck fitting be large enough for the throughput to the engine, or will you have to re-do the fitting to increase the diameter? The size will need to be dictated by the engine needs, not the heads , but you can alawys use a reducing socket (also from ASAP) to get the correct size for the heads.

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[tom52]

The seacock on the saildrive plate and the seacock for the heads appear to be the same size as does their rubber pipework. So I guess that sharing the same hull hole theoretically means that it will only be half the required size if both are currently operating with their minimum hole size.
However I cannot imagine that the occasional pumping of the heads whilst the engine is running will deprive the engine of raw water for long enough or in sufficient quantities to cause a problem, unless doing so causes some kind of airlock.

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[pvb]

Aagghh!!

Isn't this idea fraught with danger? You only need some well-meaning crew member to turn off the wrong lever and you'll cut off your engine cooling completely. If you want to go down this route, look for a seacock with locking handles so you can padlock the cooling side open.

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[tom52]

Re: Aagghh!!

The heads seacock is already next to the engine seacock near the saildrive base plate, so in theory this potential disaster could happen now. But access to either requires lifting the lid on the engine in the aft cabin so its unlikely unsuspecting crew could accidentally turn off the flow to the engine. But it certainly a thought and even if I leave things as they are I will make sure both seacocks are well marked !

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[gunnarsilins]

I have a similar arrangement on my boat, one intake, shared between two Lavac toilets and engine. The bore is the same as it originally was with the engine connected.
But, one important thing, you must use a non-return valve in the piping to the toilet, otherwise the engine will suck water (and eventually air) from the toilets.
The only, and minimal, side-effect is that the resistance is slightly higher when flushing one toilet while the engine is running. This is probably a sign of a undersized through-the-hull, but I don´t find it worth bothering.

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[andy_wilson]

You mention that you have rubber pipework in the engine compartment.

I hope you have it well lagged with heat resistant tape or similar. If you have an engine room fire you are not going to get at the seacocks are you.

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[tom52]

Thanks for that Gunnarsilins. A very good point about a non return valve in the heads pipes.
And thanks to every one else for their advice.
I think I will give it a go and abandon the struggle to keep the intake via my saildrive leg unobstructed.

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