Advice on the positioning a new Raw Water Intake

[MV-Romnya]

Thank you all once again for your previous help on fixing my overheating problem, type of Seacock to use and much more - got a seacock sent over from one of the members (HopCar), Thanks HopCar received it Monday 22/10 - Now the question is Where do I put it ? - I have 3 other seacocks (all forward of the engine) which I intend removing and clogging the holes they are all in very bad positions, the only good position is aft of the engine - will this cause poor intake whilst under way or do all intakes have to be forward of the engine ??

Advice Please - MVR

[S/V Alchemy]

You may consider the following depending on the layout of your boat: a standpipe.

A standpipe is a straight metal pipe either welded or screwed onto a thru-hull base. It can be secured by bracing if needed. It extends above the waterline and is capped with a gasketed (again, usually metal) cap. It resembles the old style oil fill tubes on the sides of North American houses from when oil was a common furnace fuel.

Down the pipe, below the waterline, are welded-on T-fitting threaded to take sea cocks. Put in as many as you need and can safety fit in regards to access.

The advantages are many in that you have only one "intake" hole in the boat. Fitted with a hinged screen or filter, you can, should you suck in fish and/or debris, open the top cap, see what's down there, and use a length of dowelling to clear the entire standpipe.

An alternative, "belt and suspenders" approach would be to have a single, large seacock near the centerline/midpoint of the boat (to ensure it is always below the waterline). Then, you tap an appropriate pipe with the required T-fitting and smaller seacocks for raw water intake, A/C, seawater domestic supply, and head, and fit it to the seacock. Then, if a T-fitting fails, you can shut off the main seacock and fix it (or reroute its hose to a spare fitting) while underway.

There is no particular reason that the seawater intake must be forward of the engine, other than that forward is usually deeper and less likely to be above the waterline or in part-spray, part-air if heeled. Getting "gulps" of air in the raw-water intake circuit could indeed lead to problems, so you have to figure out the angles. Generally, making the lower-most T-fitting on a well-placed standpipe would do the trick.

As for positioning, you can "hide" in under saloon stairs or inside a piece of galley cabinetry, just as long as you can reach all those seacocks/shut-off valves and can look down the standpipe to see blockages and deal with them.

The standpipe in my steel motorsailer saved my engine when I noticed the engine temperature rising and noted that the pump was running properly. I looked down the standpipe and saw that we had sucked in a large, thin plastic bag. I was able to push it down and out and we resumed motoring with no further incident.

[Cheechako]

opposite side of head discharge.... so you're not sucking up the wrong stuff!

[MV-Romnya]

Thank You S/V Alchemy and Cheechako - information perfect - Does distance from the Impeller matter ? - PS I Like your blog S/V Alchemy it looks extreemly cold and dangerous up in that ice - nice boat too - MV-Romnya

[David M]

Within reason, it does not matter how far from the impeller. You obviously want it deep enough in the water so that it never sucks air...or poop.

[Cheechako]

yeah, opposite side of the galley sink too in a perfect world....

[Panope]

Here is a variation of the standpipe that Alchemy suggested. The strainer and valve are both above the waterline. With strainer cover (clear plastic) removed, blockages are easily cleared with a rod. Standpipe must be well braced - in this case it is welded to hull structure. I will admit that the Vetus water strainer is a little on the flimsy side, but I wanted plastic (aluminum boat) and a bottom inlet port to allow the described cleaning ability.

Steve

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[MV-Romnya]

Thank you all, your advice was invaluable - put a new seacock in last month - works fine - now I can leave the boat for a couple of months at a time and not worry about it sinking from a hose leak or the likes because I can now turn it off when not in use - have a wonderful summer up where you can't see the Southern Cross - Karl on MVR