installing the MMI water lift muffler

[Jlmatt]

I just removed the copper jacketed pipe and what what left of the rusted muffler out of my Pearson Triton.
I got a new MMI water lift muffler and I have a 3 questions about its installation.

1: I thought I would make some kind of wooden shelf for it and glass it in on the hull, but I'm a little worried about the vibrations and the heat because the old muffler was kind of suspended by straps and did not touch any structural part of the hull. Does my plan sound OK?

2: The old muffler had raw sea water injected at the back of it, I'm not talking about the engine cooling water, but an additional hose coming directly from a thru hull, I'm not sure I understand why, maybe for additional cooling ?Anyway I would like to do away with that because it's not a proper seacock, just a plastic thru-hull with a garden hose type faucet that's half rusted out. I would like to get rid of it and plug that hole below the water line.
Is that OK? of do I need the extra cool water to cool the exhaust?

3: the outlet on the MMI muffler is 2''ID. Would it be ok to convert that to
1-5/8'' since that's what I have right now or should I get some new hose and a bigger thru-hull at the transom?

Jean-Luc

[rigspelt]

Originally Posted by Jlmatt

1: I thought I would make some kind of wooden shelf for it and glass it in on the hull, but I'm a little worried about the vibrations and the heat because the old muffler was kind of suspended by straps and did not touch any structural part of the hull. Does my plan sound OK?

Here's a photo of the waterlift muffler shelf on our C&C 27 that came with this old boat when we bought it last year. Note the hole that allows air to circulate under the muffler. The paint on the wooden shelf and the hull underneath looked fine in this 34 year old boat, so I presume that design is fine. It was for a much bigger muffler, so I am going to use two pieces of wood under the new MMI muffler to place it over the hole.

Originally Posted by Jlmatt

2: The old muffler had raw sea water injected at the back of it, I'm not talking about the engine cooling water, but an additional hose coming directly from a thru hull, I'm not sure I understand why, maybe for additional cooling ?Anyway I would like to do away with that because it's not a proper seacock, just a plastic thru-hull with a garden hose type faucet that's half rusted out. I would like to get rid of it and plug that hole below the water line. Is that OK? of do I need the extra cool water to cool the exhaust?

I am far from being an expert, but this is the first I've heard of two coolant hoses running to the exhaust. All the A4 exhaust designs I've found on the net so far just have one: the effluent from either the manifold (raw water cooled engine) or heat exchanger (freshwater cooled), discharging into the exhaust gasses just before the muffler, in such a way that the effluent does not backflow into the manifold and hence the cylinders.

Originally Posted by Jlmatt

3: the outlet on the MMI muffler is 2''ID. Would it be ok to convert that to
1-5/8'' since that's what I have right now or should I get some new hose and a bigger thru-hull at the transom?

I have the same problem and same question. I presumed there must have been some engineering reason to use a larger hose from the muffler to the transom to reduce back pressure, or improve discharge efficiency or something, but that means pulling and replacing the smaller transom exhaust throughhull, which is a fair bit of work. Perhaps Don could chime in here?

[roadnsky]

I just posted some quotes from Don in the other thread "Constructing A Hot Section" you may also want to read, but here's one from him about the hose sizes...

"We designed our water lift muffler with a 2" outlet because we believed that most sailboats use 2" hose between the muffler and transom.

I really believe you'd be OK if you installed a 1 1/4" X 1 1/2" reducer coupling and a short 1 1/2 nipple on your transom fitting. The OD of the 1 1/2" nipple should fit nicely in your new 2" ID hose. I'm no expert in the dynamics of fluid flow, but it is my understanding that the head loss associated with fittings that are slightly smaller than the general diameter of piping in the rest of the system is very small, due (I suspect) to the very short length in which they affect flow.

You could neck down to 1 5/8" coming off your muffler and then use 1 5/8" hose for the entire distance to your transom, but I believe you'd incur more total head loss.

I'd like to hear from others on this rather important issue. If it turns out that there are a lot of boats using 1 5/8" hose between the muffler transoms, we could consider offering our mufflers with outlets of that size."

Hope this helps.
-Jerry

[roadnsky]

I meant to add this from Don...

"The size and shape of water lift mufflers varies considerably, but the principle seems to remain somewhat the same. Exhaust and cooling water from the engine enter at or near the top of an enclosed container. An outlet is provided which usually extends from the top of the container, but the inside of which extends down inside the container, very close to the bottom (within an inch or so).

In operation, the water level builds up inside the container until the exhaust pressure builds up sufficiently to lift the water out of the outlet pipe (hence the name) and out through the transom via reinforced rubber exhaust hose. There is always a level of water maintained inside the container to a level just above the bottom of the outlet pipe which muffles the sound of the engine which accounts for the second part of the name."

Also, I agree with rigspelt... get rid of that other water inlet and hole in your boat!

[Don Moyer]

In designing the outlet to our muffler we went with the diameter which in our experience is the most common size hose from the muffler to the back of the boat. The fact that 1-5/8" hose is already on your boat would suggest that you're perfectly safe to continue using it.

Don

[rigspelt]

roadnsky and Don - excellent: I'll run 2" hose to the stern and downsize to the transom throughull already there. I took a look again on the boat tonight and it should be easy. Thanks.

[Jlmatt]

Thank you all for your replies, thank you Rigspelt for that picture, now I know what to do.
As far a the mysterious extra hose at the outlet of the old muffler, the more I think about it, it does not make any sense as a water entry. I wonder if it could have been to release pressure in case someone started the engine without opening the exhaust shut off valve. Hanging the ignition key on that valve should be enough to prevent that from ever happening.

JL