[C38] Exhast Mixing Elbow?

Mon Aug 1 21:52:59 EDT 2011

Hello Max and group,

Sorry for the late reply.

Max, when you said you thought the elbow heat exchanger channel was to cool the elbow, you were correct.  When I said that the idea of the water being hotter the better, I was referring to the efficiency of that heat exchanger elbow.  Obviously, if the water isn't heated sufficiently, the elbow will still be very hot and the exhaust system will also which can be detrimental to rubber components.

The hotter the water becomes before it enters the exhaust the cooler the exhaust and hoses will be.  The water and exhaust eventually going overboard will be completely mixed by that point but the idea is to mix as much temperature as possible between the hot exhaust and raw water in the early stages of the exhaust system before the rubber components of the exhaust.

As a side note, if the water in the elbow is actually changed to steam, the system gains some efficiency because changing water to steam actually absorbs more BTU's than if the water is left in liquid state.  Most raw pumps have enough volume to keep the water from turning into steam but it is nice to know that if for any reason we get a flow reduction that the exhaust cooling will compensate somewhat if the water changes to steam although not enough to compensate for the loss of volume.  Since your engine will probably suffer a nuclear meltdown anyway in such cases, any benefit to the exhaust cooling efficiency is a minor consolation.

I have a knack for making the simple very difficult.  The bottom line is that the efficiency of the heat exchanger of the elbow is important which many home made elbows seem to ignore.

Tom Troncalli

----- Original Message ----- 
From: Max Soto 
To: tdtron at earthlink.net;Catalina 38 Listserve
Sent: 7/25/2011 9:33:23 PM 
Subject: Re: [C38] Exhast Mixing Elbow?

Hey Tom,

I haven't heard this one before...
Wasn't aware that the hotter the water on the exhaust, the better...I thought that the channels on the elbow were for cooiling it, not for the elbow to heat the water.. I've been thinking about it but can't come with the right answer..Why is that recommended????????

I made mine four years ago  out of stainless pipes ( chinese stainless, so they better than galvanized and cheap) and  made an insert on the elbow that comes about  2" lower than the barbed fitting for the hose, so I was kinda worried about the top part of the hose melting, but so far, so good after 1600 nautical miles.....

I'm also planning to make another one for the new engine, but I'm taking it one step at the time!!

Regards, Max

2011/7/24 tdtron at earthlink.net <tdtron at earthlink.net>

Hello David,

Those cast iron elbows self destruct and eventually need replacing.  At
this juncture, you probably only have three viable options, either replace
the elbow with another like the original or fabricate one from stainless or
standard steel fittings.  If you decide to go the stainless route using
stainless fittings, expect to spend some real money.  The dairy and other
food industries use threaded stainless fittings but you won't find them at
your local plumbing supply.  If you fabricate an elbow from stainless pipe
instead of fittings, it will be cheaper but with more labor involved.  In
any case, there needs to be a cooling passage to preheat the hot water
discharged from your heat exchanger before the water actually enters the
exhaust.  With either threaded fittings or fabricated stainless pipe you
will have to weld a pipe to the side of the elbow to preheat the cooling
water before it discharges to the exhaust.  The hotter the water, the
better before it joins the exhaust.

As you can see, the fastest, easiest and cheapest way to fix the problem is
to just replace the #$%^& cast  iron unit.  By the time the cast iron units
fail, they are usually very brittle, thin, and the cooling passage
mentioned above is clogged from corrosion and scaling.  I have removed cast
iron elbows that didn't look very bad but crumbled in my hand when I
removed them.  Cast iron sux but it is cheap, too bad it isn't also
inexpensive.

A third option is to make the elbow from standard plumbing fittings but you
will still have to make the heat exchanger preheater for the water like
with the stainless option.  This is by far the cheapest option but like
cast iron, it will be only temporary until the steel rusts out.

I have seen people make elbows from pipe fittings with just a threaded barb
to allow the water into the elbow below the 180 degree bend without any
heat exchanger passage and as far as I know, they had good success but
Universal thought the heat exchanger passage was a good idea and they are
smarter than I am so use your own judgement on this issue.  The heat
exchanger passage definately complicates things.

I have a weld shop and I planned to build a stainless exhaust from the
manifold to the rubber hose but I ended up selling my 38 before my exhaust
failed again.

Good luck,

Tom Troncalli

> [Original Message]
> From: <david at dlrfilms.com>
> To: Catalina 38 Listserve <listserve at catalina38.org>
> Date: 7/24/2011 9:47:44 PM
> Subject: [C38] Exhast Mixing Elbow?

>
> Next stop on the tour of my engine, the exhaust mixing elbow has a crack
> in it and both water and exhaust are coming out. I've never used JB Weld,
> but thinking this might be the time to learn.
>
> Of course the elbow and nipple connecting ot the coolant tank look like
> they haven't been moved since the boat left the Catalina factory. I've
> been putting Liquid Wrench and PB Blaster on at the begining of each day
> and hope the heat and vibration is working it in.
>
> Have been having some AMAZING trips. One thing I've learned is that if I
> have happy people on my bow, I don't even mind having the engine on, but
> sailing is still best!
>
>
> _______________________________________________
> Listserve mailing list
> Listserve at catalina38.org
> http://catalina38.org/mailman/listinfo/listserve_catalina38.org

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-- 
Max Soto
C38 #198 ESTANCIA
Puntarenas, Costa Rica
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