Underwater exhaust Pros and Cons

[Lon nan Gruagach]

Are there any active silencing systems?

 

[vas]

since we start asking Qs, can I go slightly off-topic and ask if there is any cheap(er) even diy silencer solutions?
My 330hp engines with above w/l straight through exhausts sound lovely at the beginning but after 2h at pootling (sp?) speed they are tiring indeed if you want to have a conversation at the aft deck.
I do have space, I don't have a grand or so for the LS1 recommended silencers for 128mm dia pipes (iirc)

cheers

V.

 

[MapisM]

At least in my experience MapisM, the bypass outlets above w/line are for exhaust gas, and a little bit of water splutters out inevitably, but they are not cooling water tell tales (like in an outboard motor, conceptually). Manufacturers insist on them to reduce back pressure at idle, when the u/w exhaust can have perhaps 75cm of water head "blocking" it, typically.

If that is the case, I'm happy to apologize with Rafiki who was correct, while I was wrong.
A question for Deleted User, though: am I wrong in remembering your bypass outlets as being water telltales only?

 

[mlines]

These are quite cheap (and have the benefit of reducing the whine from the passenger seats)

 

[Deleted User YDKXO]

A question for Deleted User, though: am I wrong in remembering your bypass outlets as being water telltales only?

Dunno M to be honest. When I remember to do it, I do check over the back of the boat to see if there is water flowing out of the outlets on start up but I can't say whether exhaust gas is also exiting. The Ferretti manual does specifically advise that the outlets should be checked for coolant water flow on start up so I guess they are designed to be tell tales. Having said that what jfm says does make sense

 

[MapisM]

Having said that what jfm says does make sense

Absolutely.
I was only asking because I half remembered to have seen your outlets, and that they were pretty small and clearly designed just to spit water - then again, I might be confusing them with something else, like the a/c raw water outlet, or whatever.
Otoh, I am sure to have seen also other boats with a "telltale-only" outlet along the stern sides of the hull, near the w/line, but I can't for the life of me remember which is which...
...Bad thing, getting old!

 

[tico]

A friend's Broom 38 has telltales mounted fairly well forward and high enough to be easily seen.

 

[Latestarter1]

The purpose of fart pipes is primarily to relieve engine back pressure at idle when underwater exhausts are employed, yes they are useful as tell tales however that is not their main function.

CAT and Cummins installation directions both clearly state the requirement for them when underwater exhaust is employed.

Every installation I oversee has exhaust temperature alarms and in may cases additional water flow alarms.

Surprised that many high end motor yachts still have owners looking over the wall at the tell tale.

Still think that underwater exhausts suck and that their use should have ended when the last of the WWII German E Boats went out of service..............

 

[Deleted User YDKXO]

Absolutely.
I was only asking because I half remembered to have seen your outlets, and that they were pretty small and clearly designed just to spit water - then again, I might be confusing them with something else, like the a/c raw water outlet, or whatever.

Here are the outlets on my boat. TBH they look large enough to be more than just tell tales so I guess exhaust gas passes through them as well

 

[MapisM]

Still think that underwater exhausts suck and that their use should have ended when the last of the WWII German E Boats went out of service..............

P, if I will eventually abandon my boat change plans (which is very possible), some of your comments will have played a role in such decision.
I remember to have thought in several occasions that your views matched nicely the setup of my old tub, and this is yet another one.

Btw, it's not like non-u/w exhaust are bound to be noisy: as anyone who have been onboard with us can confirm, even with exhausts 1 foot or so above the w/line, she's very quiet, and leaves close to zero soot on the transom, in spite of her old mechanical engines...
...if only she wouldn't need varnishing, recaulking and so forth so often! :nonchalance:

 

[Deleted User YDKXO]

Surprised that many high end motor yachts still have owners looking over the wall at the tell tale.
.

We just can't help ourselves! We are simple people and its been drummed into us by RYA instructors and MBY articles

 

[aquatom]

I know of one forum boat that has a camera in the engine room looking directly into the bilge and the sea water strainers. Easy visual check of water flow.

Throw a couple of ping pong balls into the strainers and even better!

 

[Blue Sunray]

Throw a couple of ping pong balls into the strainers and even better!

I like that idea.

 

[vas]

Still think that underwater exhausts suck and that their use should have ended when the last of the WWII German E Boats went out of service..............

P,

care to roughly explain the reasons for this dislike of yours? Not disputing, just interested as except for the backpressure issue I cannot think of any other reason.

(and as I asked previously) any ideas for cheap silencers/mufflers/whatever you call them would be much appreciated!

cheers

V.

 

[Latestarter1]

We just can't help ourselves! We are simple people and its been drummed into us by RYA instructors and MBY articles

At nautical college I was taught, no bullied into being able to box the compass in quarter points, both clockwise and counter clockwise has it ever been any use to me nah!

When a vessel gets decent way on it the extraction effect of the main exhaust means that squat all generally comes out of the fart pipe, what does our RYA instructor do then, panic?

 

[Deleted User YDKXO]

When a vessel gets decent way on it the extraction effect of the main exhaust means that squat all generally comes out of the fart pipe, what does our RYA instructor do then, panic?

Yeah but you're not looking at the fart pipe under way, only on start up as a visual check that coolant is flowing and tbh I think thats a sensible precaution to take

 

[jfm]

Must say I'm with LS1 on this. If RYA think that checking the fart pipe is sensible they are even dafter than I thought. You need a system that will tell you if you have lost raw water coolant at any point in your voyage, not just for a few seconds after start up. That means, if you're being sensible, you need reliable heat or flow measurement in the engine rooms with alarms/indicators at the dash. Once you have all that, the fart pipe is a waste of time as a coolant flow check imho

With respect mike, there is nothing "sensible" about checking the fart pipe to see that you have coolant flow and then extrapolating to assume it will still be flowing when you look away. You had flow last time you stopped the engines, and there is nothing sensible about thinking pumps tend to fail in the first few minutes after start up, which is what "checking the flow after start up" kind of implies.

It's not even reliable. If you look at a fart pipe like yours near the waterline, you will often not be able to tell defence between the trickle of coolant water and the splashes made by the farting exhaust gas when waves/ripples reach the fart pipe outlet

Only function of fart pipes in my book is to keep Caterpillar and Cummins happy when you have deep u/w exhausts

 

[Deleted User YDKXO]

It's not even reliable. If you look at a fart pipe like yours near the waterline, you will often not be able to tell defence between the trickle of coolant water and the splashes made by the farting exhaust gas when waves/ripples reach the fart pipe outlet

I never remotely suggested that inspecting your fart pipes and checking for coolant flow at the dock could be extrapolated for the whole trip. That would be a nonsense of course. But IMHO its a belt and braces precaution to know at least that you are leaving the dock with coolant flow and then of course, as I said, you are reliant on sensors to tell you if anything is amiss

Take your point about differentiating between coolant flow and exhaust gas splashes. I shall inspect my fart pipes next time with renewed interest but from memory I get a fairly solid flow of water