Draining Exhaust Silencers

[Illusion]

Our boat is being lifted in a few weeks time and a neighbouring berth holder mentioned to me about draining down the exhaust silencers before the lift.
Well in 8 years of owning a shaft drive boat, this is the first time I've come across this, although on closer inspection I can see instructions to do so on the silencers themselves.
I found this discussion on the topic back in 09, which seems to elevate fears, but just wanted to see if anyone else had a view point or did indeed drain theirs down for each lift as per instructions?

http://www.ybw.com/forums/showthread.php?202926-Draining-exhaust-silencers-for-lifting

Thanks

Phil

 

[jimmy_the_builder]

Our boat is being lifted in a few weeks time and a neighbouring berth holder mentioned to me about draining down the exhaust silencers before the lift.
Well in 8 years of owning a shaft drive boat, this is the first time I've come across this, although on closer inspection I can see instructions to do so on the silencers themselves.
I found this discussion on the topic back in 09, which seems to elevate fears, but just wanted to see if anyone else had a view point or did indeed drain theirs down for each lift as per instructions?

http://www.ybw.com/forums/showthread.php?202926-Draining-exhaust-silencers-for-lifting

Thanks

Phil

Evening P

I think the points made in that old thread are still correct. in my P42 there were drains at the bottom of the silencers which dumped the content into the bilges; but when the boat was lifted (just the once in my ownership) iirc they weren't drained. In your position, I'd ask and follow the advice from the yard doing the lifting (RK?)

 

[Illusion]

Evening P

I think the points made in that old thread are still correct. in my P42 there were drains at the bottom of the silencers which dumped the content into the bilges; but when the boat was lifted (just the once in my ownership) iirc they weren't drained. In your position, I'd ask and follow the advice from the yard doing the lifting (RK?)

Evening Sir, eagerly waiting on news of the relaunch, must be any day now?
We're actually being lifted in the marina this year for one reason and another, however I did speak to the yard who's definitive line was they don't get involved with this and referred me to speak with one of their on site engineering tenants.
Not to helpful but made me wonder how often the issue comes up from other owners?

 

[jimmy_the_builder]

Evening Sir, eagerly waiting on news of the relaunch, must be any day now?
We're actually being lifted in the marina this year for one reason and another, however I did speak to the yard who's definitive line was they don't get involved with this and referred me to speak with one of their on site engineering tenants.
Not to helpful but made me wonder how often the issue comes up from other owners?

Sposed to be tomorrow. Was going to be today but we had a last-minute hitch with a bit of bathing platform trim. I'll be around tomorrow afternoon if you are wfh?

It's up to you, but tbh if you're being lifted in the hoist and then on to blocks, I don't think I'd bother. Have a word with Dave Moore and see what he has to say. What did the previous owners do?

 

[jfm]

Hi P. You gotta look at design of silencers. On my squads 58 the silencers drained 75pc by gravity so there was no point opening the valve to drain mere dregs. On the 78 they drain fully underwTer and don't even have drain valves. But these are vertical cylinder silencers. On targa 52 fe the cylinders are iirc horizontal and from rough memory may contain more then dregs after boat is lifted. I dunno about targa 47

The critical point is that if the standing water in the silencer (after the boat is lifted) is close to tipping over back into the turbos then you must drain. But that is rare circumstance. You can tell just by looking at shapes

Couple of yeArs ago mby ran article on sq 58 transported to med and then hydraulically locked. Big expensive rebuild of d12. Owner blamed failure to drain silencers and rough sea on delivery voyage ( deck cargo) causing standing water to tip over. I'm not convinced but maybe it was very rough. With a crane lift your boat won't see more than say 5 degrees inclination so water won't tip over. As I say i never drained sq 58 silencers for marina lift out though I did on delivery voyages

 

[MapisM]

The critical point is that if the standing water in the silencer (after the boat is lifted) is close to tipping over back into the turbos then you must drain.

Geez, that would be a poor design indeed. What if you must cruise for some time (possibly in rough sea) with only one engine running, for whatever reason?

Fwiw, what I get done on my boat before the winter liftout and storage is a short engine run with the seacocks closed and the strainers open, feeded with freshwater+glycol.
As soon as the blueish water comes out of the exhaust, the engine is turned off, and that's it.

Of course, for some folks with an integrated fresh water flushing system that would be even easier....

 

[jfm]

Tee hee! I agree re poor design and I've never come across a fine balance case in real life. I drained my sq58 when shipping due to OCD really. I'm just not sure whether some silencers that are horizontal are possibly a case of such poor design hence my comment to illusion. And I'm sceptical about the mby article, which wAs a tall vertical cylinder silenced boat.

 

[Illusion]

Hi P. You gotta look at design of silencers. On my squads 58 the silencers drained 75pc by gravity so there was no point opening the valve to drain mere dregs. On the 78 they drain fully underwTer and don't even have drain valves. But these are vertical cylinder silencers. On targa 52 fe the cylinders are iirc horizontal and from rough memory may contain more then dregs after boat is lifted. I dunno about targa 47

The critical point is that if the standing water in the silencer (after the boat is lifted) is close to tipping over back into the turbos then you must drain. But that is rare circumstance. You can tell just by looking at shapes

Couple of yeArs ago mby ran article on sq 58 transported to med and then hydraulically locked. Big expensive rebuild of d12. Owner blamed failure to drain silencers and rough sea on delivery voyage ( deck cargo) causing standing water to tip over. I'm not convinced but maybe it was very rough. With a crane lift your boat won't see more than say 5 degrees inclination so water won't tip over. As I say i never drained sq 58 silencers for marina lift out though I did on delivery voyages

Hi JFM,

Thanks I wasn't actually aware that the designs differed so much, but your quite right clearly this and all the resulting angles will play their part

I've taken a photo of ours today which I assume is standard T47 fit out?

Seems plausible sea water will come into the silencer from the exhaust tube (right hand) however the angle then up to the engines is pretty significant, so the boat would have to be seriously nose down in the slings to allow this to occur.

Maybe worrying about nothing and why it's probably never been done or been mentioned before.

 

[MapisM]

Seems plausible sea water will come into the silencer from the exhaust tube (right hand) however the angle then up to the engines is pretty significant, so the boat would have to be seriously nose down in the slings to allow this to occur.

Well, it ain't so plausible, actually.
I mean, also the pipe coming out from the silencer is supposed to be a bit angled downward - and in fact it looks like it is, in your pic.
Therefore, with the boat levelled and the engines turned off, there should still be some water inside the silencers, but only up to the lower part of the outlet pipe. Which in turn means that also the pipe getting into the silencers remains filled in its lower part, up to the very same level.
Your pic doesn't tell the whole story though, because it doesn't show (and I don't know the T47 well enough to tell) up to which height the elbow riser goes, behind the bulkhead on the left side of your pic.
In fact, that matters much more than its angle, because unless the pipe follows upward enough to reach a height well above the water level inside the silencer (but I bet it does!), the risk of water reversal remains high regardless of the angle.

 

[Illusion]

In fact, that matters much more than its angle, because unless the pipe follows upward enough to reach a height well above the water level inside the silencer (but I bet it does!), the risk of water reversal remains high regardless of the angle.

MapisM, yes of course I understand what your saying. Any sea water above the line of the bottom of the exit exhaust will just be pushed out through the exhaust when the boat's running. I assume when you drain it off, it will just empty into the bilge?
I will check the height again later when I'm at the boat.

Thanks

Phil