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Date Posted: - Saturday - 07/ 2/11 - 12:09am
Author: Randall, Murre, M31
Subject: PVC it is...at least for now
In reply to: Randall, Murre, M31 Hull #150 's message, "Engine Exhaust issue" on - Monday - 06/27/11 - 12:55pm

Well, I think I'm going to give Mark's PVC option a try.

If I measured correctly today, the inside diamter of the exhaust hose I have is just shy of 2 inches and very close to 5 cm, which just happens to be the outside diameter of PVC I was able to find at the ONE local (15 minute row and 1/2 mile walk) hardware store. And they had four 90* elbows. And they had cement (though no primer). Amazing. Thought for a moment I was at Home Depot, except the staff was helpful, all six of them. And they understood me when I said or pointed to the French words I'd written in my note book, like:
Pipe--Tayua (not conduit)
Elbow-Cotes
Inside Diameter--Diametre Interieur
Glue/cement--Colle
Coupe--to cut (to a length)

It all worked in one go--at least as to aquisition of materials. Cost: $60 US.

This is going to look like a hack job, but all in the name of no salt water in the engine.

--

Am concerned about the heat issue. PVC is rated to 140*. I know Murre runs at about 180* But, Mark, if you've had this in place for years, then...

--

Plan to create one rise aft, near the through hull, for now.

--

Any last minute suggestions...? Will attempt this tomorrow...

RR

Aboard rolly rolly Murre
Taiohea Bay, Nuku Hiva, Marquesas

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Replies:

[> [> Exhaust temp is much lower than engine coolant temp -- Paul M31 #106 NJ, - Saturday - 07/ 2/11 - 9:06am

The only influence the 180 degree engine coolant tem has on exhaust temp is at the water cooled exhaust manifold. The (dry) exhaust is cooled somewhat there but definately not all that much. The real cooling happens at the raw water injection elbow where the exhaust gets mixed with seawater after it is done cooling the heat exchanger, oil cooler and tranny cooler. Then the exhaust gases literally pushes the raw water from the water lift muffler into the exhaust line to the through hull - well cooled at that time...

The only downside I see with where you propose to put the loop is that, since the exhaust line is sloped down towards the thru-hull, you will have standing water in that hose from then on when the engine is shut off - instead of the hose draining as was designed. With my system, all hoses drain - either back into the water muffler or overboard, once I shut off the engine.

But it should help you keep the ocean out of your exhaust manifold for now.

Will you be able to also put in some vacuum break?

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[> [> [> Exhaust plumbing -- Mark Aeolus M31, - Saturday - 07/ 2/11 - 3:11pm

Randall, glad to hear you could find the needed parts that easily. If I understand, you're going to put the loop aft close to the through hull. On my boat the PVC lift muffler is attached to the lower front side of the fuel tank, so the water that flows back into the muffler when I shut down is minimal (just the vertical rise to the underside of the cockpit seat.) Just make sure that if your muffler is lower than the loop your installing there won't be more water backing into the muffler than it can hold when you shut down. Hope that makes some sense? Mark

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[> [> Job Done -- Randall, Murre, M31, - Sunday - 07/ 3/11 - 2:37pm

Thanks Mark and Paul for last round of advice.

Paul, on Murre the thru hull was actually AT or ABOVE the Aqua Lift muffler. (Done so before I bought the boat and in all these years I didn't catch the problem--worthy of ridicule: both the install and my failure).

Per your collective suggestions, I did move the rise forward a bit. So the run forward of the rise is now roughly equal to what it was before I added the rise, maybe a little less.

Though I measured THRICE, the exhaust hose was not 5cm ID as the OD of the fiberglass elbow going into it from the Aqua Lift suggested, but was inch or more smaller. (Not discovered as such until the hose was cut and I was thus beyond the point of return. This represents some sort of universal law that I wish we could repeal.) So, spent most of my time fashioning plugs to drive into the steel reinforced hose to expand it. One hose clamp is all I could fit on either side. Unfortunately this is the weakest part of the install, but Ive tugged pretty hard at these connections and theyve not budged.

The rest, cutting and gluing, was pretty straightforward. Whole job held in place with zip ties for now--all I have. But is solid.

Providentially, I happened to find a small piece of flexible ***PVC*** hose at the side of the road while walking back from the hardware store with my PVC pipe, which I have added to the top of the rise as a siphon break (cemented in place). Have run it for now into the cockpit where it dribbles a tiny bit of exhaust water when the line is under pressure--indicating water is passing through the exhaust hose without my having to lean over the stern.

Ran the engine for an hour and all appears to be well. To your points re heat issue, PVC was warm to the touch after an hour, but just that, so, was well below the 140* rated temp, Id guess.

Real test will be the 450 mile run to the Tuamotus coming up in a couple days.

Pictures here: http://www.flickr.com/photos/63439824@N04/sets/72157627107299856/detail/

Thanks all (inluding Bruce, with whom many emails) for the feedback.

RR

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[> [> Tuamotus -- Lawrence Killingsworth M40 Ta' Ata Ori, - Tuesday - 07/ 5/11 - 1:02pm

When you get over to the Tuamotus, Randall, make sure you stop at Rangiroa Atoll. I was there a couple of years ago, on the brigantine Robert C. Seamans. The snorkeling in the lagoon is marvelous, you can sip a cold brew in the on-the-water bar at the Kia Ora Resort and you can even pick up some black pearls for your BWW. Happy sailing!

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