400 muffler raw water hookup?

Does anyone know what the purpose of the muffler raw water hookup in this picture is for and does it need to remain open underway? The boat is a 2004 Mainship 400 with a single CAT 3126. We've been looking at this boat for possible purchase and wonder if there are any general (or specific) pros and cons other folks have. Thanks in advance! Karl

I can only guess. Try the Mainship owner's Forum. But be aware, Mainship's had some interesting water back flow issues that are model, year, engine and user specific. Be careful and questioning, buying a previously flooded 3126 can get expensive.

We have a Mainship with a 370 Yanmar it also has a raw water discharge from the muffler, looks like a 1-2 inch hose. What is it for ?? do you need to drain this hose when winterizing the boat with pink antifreeze ?


Thanks Ray

sunchaser said:

I can only guess. Try the Mainship owner's Forum. But be aware, Mainship's had some interesting water back flow issues that are model, year, engine and user specific. Be careful and questioning, buying a previously flooded 3126 can get expensive.

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Thanks for ur response, I appreciate the input. I had read about some back flow issues but I don't think they occured to this boat since it has about 2000 hours on the engine and it has been seasonally cruising from New Hampshire to Florida for the last several years. I haven't physically seen this Mainship yet, just pics from the broker. Any purchase we make will definitely be contingent upon separate surveys for boat AND engine. One thing I have noticed on any Mainship 400 I've seen is the shutoff valves in the below deck cockpit drain lines going out through the transom. I assume those are to help stop backflow through those hoses. In any case, I may be missing it but I didnt find a Mainship owners group link when I googled... Just a yahoo list of some sort. Do u happen to have the Mainship owners group site url? Thx

Ray said:

We have a Mainship with a 370 Yanmar it also has a raw water discharge from the muffler, looks like a 1-2 inch hose. What is it for ?? do you need to drain this hose when winterizing the boat with pink antifreeze ?


Thanks Ray

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Hi Ray, I'm no expert on exhaust systems or the physics of water pressure and flow, but from the pic, the line seems like it goes to a thru hull and be a supply line rather than discharge, but I could be wrong. The connection is fairly high up on the rather large muffler. I didn't know if it was a water lift muffler of some sort and this line in some way helps ensure adequate exhaust cooling water level. I haven't looked at a zillion boats but I also haven't noticed this type of setup before...including on other Mainship 400s we've looked at. And yes, I think you'd want that muffler and line to either be empty or full of the pink stuff if your boat will be stored in a cold climate where freezing is possible.

I had something similar on my 2006 Mainship 34T with a single Yanmar 370 hp engine.


That hose is an equalization line. Any water that backs up from the exhaust into the lift muffler will never rise above the seawater level due to the equalization line. This protects the turbo and engine from getting seawater backed up into it.


Otherwise waves can push water back into the lift muffler and fill it up above the sea water level and flood the engine.


Sailboats solve this problem with a high exhaust loop after the lift muffler, but as you can see from the pic the exhaust goes straight back and out.


David

Agree, it's a high waterlevel drain for the muffler. It would keep the muffler level at the WL level should water roll back down the hose from the transom and fill the muffler (such as could happen while anchored in a seaway) or cranking excessivly w/o starting. Usually, and more safely, this is handled by a 12" minimum gooseneck at the transom. One would have to access this unusual feature with respect to the entire exhaust system to decide if it is well founded. Making an elevation sketch, including the vessel WL, spillover point, and other important elevation measurements and sending it to a supplier like Cetek sp? as a proposed system would be a good idea if you could get them to comment.

[QUOTEIn any case, I may be missing it but I didnt find a Mainship owners group link when I googled... Just a yahoo list of some sort. Do u happen to have the Mainship owners group site url? Thx ][/QUOTE]

That is the Mainship owner's group site.

djmarchand said:

I had something similar on my 2006 Mainship 34T with a single Yanmar 370 hp engine.


That hose is an equalization line. Any water that backs up from the exhaust into the lift muffler will never rise above the seawater level due to the equalization line. This protects the turbo and engine from getting seawater backed up into it.


Otherwise waves can push water back into the lift muffler and fill it up above the sea water level and flood the engine.


Sailboats solve this problem with a high exhaust loop after the lift muffler, but as you can see from the pic the exhaust goes straight back and out.


David

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Thanks! Great info.

jleonard said:

[QUOTEIn any case, I may be missing it but I didnt find a Mainship owners group link when I googled... Just a yahoo list of some sort. Do u happen to have the Mainship owners group site url? Thx ]

Click to expand...

That is the Mainship owner's group site.[/QUOTE]

Thanks JL

Brooksie said:

Agree, it's a high waterlevel drain for the muffler. It would keep the muffler level at the WL level should water roll back down the hose from the transom and fill the muffler (such as could happen while anchored in a seaway) or cranking excessivly w/o starting. Usually, and more safely, this is handled by a 12" minimum gooseneck at the transom. One would have to access this unusual feature with respect to the entire exhaust system to decide if it is well founded. Making an elevation sketch, including the vessel WL, spillover point, and other important elevation measurements and sending it to a supplier like Cetek sp? as a proposed system would be a good idea if you could get them to comment.

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Thanks for the info and suggestion!

In order for your engine to be truly protected from salt water intrusion, it must have a high point that occurs in the dry section of the exhaust, which is to say right out of the turbo or exhaust manifold, to a point high enough that the wet portion of the system can have adequate slope to drain off any water that finds its way in, whether through the transom outlet, or from cranking without starting the motor.
That said, many manufacturers of boats seem not to understand gravity and its effect on liquids.
I have worked on numerous yachts (including Mainship) that were entirely flawed in their exhaust design, and some of them have gotten away with it for years, while others regularly get new motors instead of addressing the real problem.
Just because it came from the factory like that doesn't mean that it is proper.
The muffler drain thing is a lame attempt to correct obvious design problems.