Engine/Gen Separated Exhaust

[Muaddib1116]

My boat's Yanmar 4JH110 and generator both have separated exhausts. Is this necessary? I sort of understand the benefit with the generator, it keeps things quieter while it's running at anchor. I'm not sure what the benefit is for the main engine, at cruising speed, you wouldn't hear the water in the exhaust, and the "dry" tends to spew out a decent amount of water anyway.

I'm not a big fan of where the water outputs. The "dry" part exhausts out amidships on the starboard side. The water exhausts out of below water thruhulls that are very close to a lot of electrical equipment (battery box, bus bars, chargers, etc.).

I'm wondering if it's possible to just remove the water separation boxes and route the mixed exhaust directly out the existing ports that are at the waterline on the starboard side. Does this cause problems for the engine or generator? The biggest downside seems like I'll have some more exhaust noise when the generator is running, but I'll be able to remove and glass over some thru hulls that are near delicate equipment.

I appreciate any advice.

[skipperpete]

Give up on this idea,even with a dry exhaust it won’t work. The potential damage to the idle engine is simply not worth the risk for no real gain. It’s already hard enough to stop single engine wet exhaust’s from putting raw water into the cylinders without adding a whole new level of difficulty
It could be made to work with a great deal of planning and a couple of electrically operated valves in each exhaust prior to the Y but a 100mm electric valve and a 50mm for the genset will cost a lot of green.
OOPS! That’s the wrong answer...... I just re read your post and realized that your exhaust IS dry from the water separator and you want to make em both wet to the overboard

[BillKny]

I think Pete made the same mistake I did the first 4 times I read your post.

If I am now correct, you do NOT plan to combine the engine and generator exhaust into a common outlet, rather you just want to lose the water separators and run the exhaust/water mixture all the way to two thruhull fittings, one for each engine.

That MIGHT be possible. But the new configuration needs to be carefully reviewed by someone who knows exhaust systems very well to be sure you don’t increase the risk of flooding the engine or generator. The is important, and not to be taken lightly. You don’t have to read very long on this forum to see that water flooding is the cause for a lot of premature engine deaths on sailboats.

The water separators add a lot of volume, and if installed correctly, make engine flooding less likely when sailing.

I do not believe this is worth the effort and increased risk to the engines, no matter how small. Properly maintained hose and seacock systems do NOT leak. I have a similar arrangement for water discharge lines on my boat, and it gives me no concern at all. Of course if you do no maintenance UNTIL they leak, then the fault is not the design.

[Muaddib1116]

Yeah, I think I did a poor job of explaining it, and probably used the wrong terminology. Each engine has it's own independent exhaust, and I'm happy with that. Both engines are raw water cooled, like most marine diesels, and they output mixed exhaust from the engine. That mixed exhaust goes to a water separator box, and the "dry" exhaust goes out through above-water holes amidships, and the water goes out underwater through a thruhull. Most boats don't have water separators for their exhaust. Are they just to make things quieter? or are they necessary for the engine to run properly? or are they no strictly necessary, but beneficial?

It seemed to me that it was a sort of optional "upgrade". As I mentioned, when I'm at cruising rpm, the main engine's "dry" exhaust is outputing a fair amount of water anyways, so clearly the water separator has limits. And it seems like any device (like a water separator) in the exhaust line would only add back pressure.

The seperator boxes are up at about deck level. The exhaust comes up from the engine into the box, and then back down, one pipe to the midships hole right above the waterline and one down to the thruhull. If I got rid of the separator boxes, and still ran the exhaust up and over an above-water bend and then down to the midships above-water hole, how would that increase the risk of water getting in the engine? It seems like it would be removing complexity and possible failure points, not adding them.

I would definitely consult an engine/exhaust expert if I chose to change anything, I just wanted to know if it is a doable thing before going through the effort of finding an expert and taking up their time.

[tkeithlu]

I've adopted the policy, when looking at something on Amazon, at Harbor Freight, or on my boat of asking myself "How much will owning this or changing this improve the quality of my life?"

So, what's the advantage of doing this? Surely there are improvements to your boat that you can think of that really step up your quality of life. How about an automatic solar powered margarita maker?