We had a fabulous Groco anti-siphon loop. Emphasis on had.
It was a big, bronze thing that worked nicely for about 10 years. Then. It developed a tendency to drip.
If you're not an engine-room nerd, that's wire-reinforced 1″ hose coming into the bottom. ⅝″ coming out the top.
The cooling water comes up the far side of the arch and flows down the near side into the exhaust gas. From there the mixture goes to the muffler. From the muffler, water flows up over one more arch above the water line and then down the exhaust hose and out the back of the boat.
The flared out section on top of the near-side of the anti-siphon loop has a one-way valve. If water starts to siphon through the loop; it pulls the valve open, and the air breaks the siphon. It saves the boat from the unlikely event of water being pushed backwards through the exhaust system and siphoning through the engine block.
(Imagine a giant wave crashing over the boat and filling the exhaust system with water. Or maybe don't imagine that. But this prevents one of the horrible follow-on scenarios.)
The hose coming out of the flared out section is because the damn thing weeps. Just a little. You can see the oxidation of water weeping down this.
The starter motor.
I cleaned and dry lubed the valve until I was sick of cleaning and dry-lubing it. It was weeping so badly that I ran 10′ of hose from the vent in the top down into the bilge to save the starter motor.
It's ten years old. I'm not surprised that it's gotten weepy and drips. (Insert old man joke here.)
I'm not sure I needed to replace it. But I did. (I'm keeping it as a spare. It's super-rugged, and you never know when you might need to replace it.
Here's the new Vetus anti-siphon.
It's small. It's plastic.
It's very well-made.
But it's small. And plastic.
The Vetus owner's manual says — specifically — it will drip. Because it's small, I can run a small tube down into the bilge so it won't drop on the starter.
This was the same solution as the Groco, exception with smaller hose.
I'm not sure this is a real victory. I expect the Vetus to weep less for the next 10 years. After that, maybe I'll put the Groco back. Or. Maybe Vetus sells the anti-siphon valve assembly as a separate thing that I can replace.
You may ask what the four hose clamps in the bottom of the picture are. That's the splice between 1″ hose at the loop and 1⅛″ hose going into the exhaust riser.
Single hose clamps on the anti-siphon? It's above the water line. The hose barb is 15cm, about the width of a common hose clamp (½″ ≈ 13cm).
I have an uneasy feeling that the far-side hose might 1⅛″. There's no visible logo; meauring OD isn't reliable; the ID shows a bunch of wear. I don't recall having to mush it hard on the Groco. But. Maybe I did. It was 10 years ago.
The Vetus barb is 25mm. 1″ hose is 25.4mm. 1⅛″ hose. The gap is ⅛″ plus a bonus of a hair-thin 0.4mm. The first test had some tiny weeping from the hose clamp. After that, I really mushed the host down hard onto the Vetus. Wrench-tight. We'll be monitoring and seeing if we continue to have a hose clamp dribble and need to splice in a foot of 1″ hose (and 4 hose clamps) to prevent weeping.