Exhaust system for Self righting vessel

[steve123]

Hi,
Finding information on exhaust system for self righting vessels is proving very difficult. Looking at how best to configure the system on 14m vessel with twin engines.
Any help..ideas..information would be much appreciated.

 

[gonzo]

Is it a wet or dry system?

 

[dougfrolich]

Check the SNAME library for the USCG 47ft Motor Life Boat. A very well done explanation is given there.

 

[steve123]

Cant find it on SNAME site...Guess dry system would be easier but if there's a good system for wet then prefer wet to keep heat down.

 

[dougfrolich]

Water trap type mufflers if used need to be large. If one engine operation is anticipated then maybe some time of redirect should be incorporated. Also engine air intake vents should be located above the inverted waterline to keep water out of the engine room. Also keep in mind that there could be lower pressure in the engine room due to the engines aspiration consuming air and pulling water into the space.

 

[keysdisease]

Doug, your drawing appears to have the two lift mufflers connected?

I can't imagine that being a good setup with only one engine running, looks like a potential back-flood problem for the off engine.

 

[dougfrolich]

Yes I agree the cross connect could be a problem when running on a single engine.
I think the key to minimizing the potential of flooding the off engine is to make the mufflers large, and the rise high above the muffler--better yet incorporate a gate to close the cross connect when running on one engine.

 

[keysdisease]

I can't imagine why cross connecting the mufflers is a good thing under any circumstances, even a knockdown or rollover.

Doesn't matter how high you make the riser to the muffler, water is going to take the path of least resistance (downhill) and is going to fill the off engine muffler and back up to the exhaust manifold/turbo long before it chooses to travel uphill. If the vessel was always level this "might" work, but in a seaway water moves around like its alive. Backflooding may even happen with one engine running slower or with a cylinder(s) not firing on one engine.

And as far as a valve between the units, who's going to remember to close it? When you're on one engine that means something is most probably wrong, and attention on a small vessel may be directed to something of a higher priority than a valve between the mufflers which is probably buried anyway. Accident waiting to happen IMHO

 

[Chuck Losness]

One of my good friends is a retired coast guard who ran those rescue boats at the bar of the Columbia River. At the end of his career he spent 7 years as an instructor teaching the newbies how to handle those boats. They could survive a rollover (he had been rolled a couple of times) and make it back to port. But the boats always suffered extensive damage. Basically everything was wiped clean off the decks and anything that wasn't secured below went flying, including crew members who weren't strapped into a chair. I can't imagine what you are expecting to encounter with the need to survive a rollover with a functioning vessel.
Good luck.

 

[FAST FRED]

" Basically everything was wiped clean off the decks and anything that wasn't secured below went flying, including crew members who weren't strapped into a chair. I can't imagine what you are expecting to encounter with the need to survive a rollover with a functioning vessel."

Folks go over Niagra Falls in a barrel for sport ,

perhaps rolling about a breaking inlet is a new sport being developed?

 

[keysdisease]

"They could survive a rollover (he had been rolled a couple of times) and make it back to port." Thats the idea.

A "knockdown, rollover, self righting" specification is not typical but it does get called out for certain type vessels. The types you would expect, military, Coast Guard, rescue, etc. You sometimes see it on an expedition yacht.

These spec's are typically for the driveline, and there are engine mounts that meet the rollover (inverted) requirement. An engine coming adrift in a violent seaway can really ruin your day.

 

[steve123]

For those of you who may be interested in the reason for the link between the two mufflers.
When the vessel rolls over one exhaust is submerged, back pressure in that exhaust can stall the engine if there is no link.