Exhausting below the waterline

[Snotter]

I am in the process of installing a genset in my Morgan OI. The engine room is below the center cockpit and is a fair distance from the transom. The generator is 7.5kw and is coupled to a 2 cyl diesel. I am trying to decide how to run the wet exhaust. It would be a lot simpler to exhaust below the waterline via a seacock. Does anyone know the draw-backs of such an arrangement? How much more fuel would be burned fighting water pressure? Would I need a muffler if exhausting below the waterline? It would be a hassle running stiff exhaust hose and cutting through a number of bulkheads. Side-exiting the exhaust can't be done in the vacinity of the engine room because of a 120 gal fuel tank, a head, and a very cramped locker that is filled with a holding tank and a heatpump. Please help keep me from folly.

 

[Roger Long]

Please help keep me from folly.

Diesel engines hate exhaust back pressure. It's not the fuel cost you need to worry about, it's the maintenance. Listening to a generator is also bad enough without adding the burble.

If you can't get to the transom, a side exhaust will only let you run at anchor or on one tack.

Pumping that water through the exhaust hose all the way up to the transom is also going to be a back pressure issue. You may find, if you talk to the manufacturer, that just a dry pipe of that length will void your warranty. You might need to go to an oversized and heavily insulated dry pipe with water injection near the end.

No easy answers here I'm afraid.

With all that real estate, might solar not be a better answer? People anchored nearby will thank you.

 

[Bill Roosa]

an exhausting issue

I'd not be plumbing exhaust below the waterline for the following reasons:
You would need a sea cock (and remember to open and close it), an anti-siphon loop (and the space to install it), you can never check for exhaust smoke or cooling water flow (and would have to do more preventative maintenance to insure the unit stays up to snuff), you'll have to listen to the burble in addition to the normal noise (this is quite objectionable to others outside the boat), you'll have to try and keep an anti-siphon loop valve clean and operating in an exhaust gas environment (most are water only loops and exhaust is pretty hot and corrosive so you will need a special valve that can take that).
And most damning, it is bad practice. Sea water in a tube that connects to an exhaust manifold is just asking for corrosion of the exhaust valves.
The pros are it would be easier to install. this is a one time thing and given all the additional items of concern seems (to me) to be a pretty poor reason to not install it "right" even though it is hard to do. You'll save yourself a lot of work later by doing it right now.

 

[RAD]

Does your engine exhaust exit the transom? can you follow the same route and piggyback the exhaust hose to the original?
I have an Oday 32 cc and my exhaust runs through the aft cabin under the bed and if I were to install a gen-set (if I could fit one) thats how I would run it and you really want the exhaust exiting the rear of the boat to prevent carbon monoxide poisoning

 

[Steve Dion]

I would think if you put a water muffler in the exhaust line you should be able to find some place for the exhaust to exit above the water line. They come in all sorts of sizes and shapes so helpfully you will find one that will fit.

Check out Vetus to start. They have a good selection, but there are several other manufactures too. Be sure that you do not undersize the exhaust less back pressure is best.

 

[kloudie1]

MAN !! I'd do whatever necessary to have that exhaust above water normally.. The noise will make you crazy if you're outside with it running.. My boat squats enough under power (all 34's) to have the exhaust slightly below the water when close to hull speed and sitting at the helm, the noise is incredibly annoying !!!

 

[Snotter]

Crap; I just knew you all would talk me out of the simple approach.

 

[RAD]

Crap; I just knew you all would talk me out of the simple approach.

At least your not doing the job twice! so if its a pain in the butt to do once then thats like doing it twice

 

[RichH]

The 'problem' with in water discharge is the 'thermal differences' ... and when the engine and especially the hot exhaust gallery, etc. cools down, you can potentially develop large vacuum pressures .... and 'back flood' the engine through the exhaust system. An above the water discharge creates an automatic 'vacuum break'.

 

[Snotter]

Maine Sail told me once to always use two vented loops, one in the water line between the heat exchanger and the mixing elbow, and one in the exhaust between the mixing elbow and the muffler. I'll do the same with the genset.

Each time the exhaust from my perkins auxhilary engine passes through a bulkhead, the exhaust hose transitions from rubber composite to a steel nipple and then back to hose again on the other side . I guess I should do the same with the exhaust from the genset.

 

[Bill Roosa]

Can you tee into the engine exhaust??? Probably have to be after the muffler as the smaller genset engine might (or maybe it would, don't know) not have enough exhaust volume to push the water up and over the siphon.
Just a thought.

Good luck

 

[Alex Dare]

back pressure

Yup, the back pressure will gunk up the valves and they'll start to stick.

 

[RichH]

Can you tee into the engine exhaust??? Probably have to be after the muffler as the smaller genset engine might (or maybe it would, don't know) not have enough exhaust volume to push the water up and over the siphon.
Just a thought.

Good luck

Might become a 'resonator' instead of 'dampening' the sound.

 

[Roger Long]

Can you tee into the engine exhaust???

Don't even think about it.