Engine anti-siphon needed?

[sgbernd]

I am getting ready to re-power. I currently have a Volvo MD7 with no anti siphon on the engine which has worked fine for 33 odd years. In trying to spec spec the new engine, I am told I should have an anti siphon in the exhaust.

To my way of thinking, if the mixing elbow is higher than the water line in all sailing conditions (it is) and the exhaust exit is above the waterline (it is), and the rise of the exhaust pipe between the muffler and exit is high enough that trailing seas cannot make it over the hump to the muffler (it is), there is no possible reason for an anti-siphon.

Is my logic correct? I am not interested in buying "peace of mind", just if it will pose any danger of water ingress to the engine. Any experiences with this?

-Steve

[hilbert]

Germane to the topic:
http://forums.sbo.sailboatowners.com/sh ... post596687
Steve, how much higher is the mixing elbow than the water line in your installation and how are you sure that it remains higher under all sailing conditions?

I would love to have engine access as pictured, but I would settle for it to be as clean. At first glance, I thought that it was a picture of an engine in a showroom.

[Jim Walsh]

I would love to have engine access as pictured, but I would settle for it to be as clean. At first glance, I thought that it was a picture of an engine in a showroom.

That engine access is criminal

[tjr818]

Zelda,
Your Bulkhead to Bulkhead carpeted engine room might have some competition

[sgbernd]

Yes, that engine room in the picture is certainly beautiful. Mine does not and will not be nearly so clean or accessible (sigh). Maybe my next boat.

Anyway, the top of the mixing elbow is 250 -300mm above the water line at rest and pretty near the center line of the boat. As she heals, the water line will never be over the mixing elbow unless I am sinking and then I have bigger problems to worry about.

I think I will skip the siphon install, then test it by pulling the water injection hose off the mixing elbow and seeing how low it must go relative to the w/l to begin trying to drip. That should tell me the answer as to whether I should put one in or not.

Steve

[Jim Walsh]

I'm pretty sure the engine in the photo is the M25-XPB, which is what I have. The interesting part is that my anti-siphon is installed exactly as in the photo and appears to be at the same height over the engine. It helps to validate ones installation when you see another boat builder with the same component placement.

Note that I replaced my engine in 2007. The original engine was the M-25.

[hilbert]

Yes, that engine room in the picture is certainly beautiful. Mine does not and will not be nearly so clean or accessible (sigh).

Can't do much about accessibility on a 28, but it is an opportunity to clean up and paint the space.

If you do decide to add an anti-siphon, it is not complicated or expensive (at least in the context of re-powering). I just redid the anti-siphon on my 28. It's mounted under the starboard cockpit seat:

[Ron M.]

Re-powered 5 years ago with Volvo D1-20. Manufacturers Installation instructions were adamant the anti-siphon vent be included and depicted examples of the procedure. Not doing so may void any warrantee. As mentioned in previous post, it's not much of a job or expense.
i was able to get it in on the bulkhead above the engine. Put in one of those 6" round access ports on the cockpit companionway wall to get at it.