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Old 18-02-2021, 11:15   #16
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Re: Do you have an exhaust out the midship side?

Auspain, You are talking about a dive boat. That means divers in the water. That is a different situation for exhaust, at least in my mind. In a previous life I was aware of a diver dying when she tried to do some work under the swim platform with a genset running. It was a still day, and CO had accumulated.
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Old 18-02-2021, 11:19   #17
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Re: Do you have an exhaust out the midship side?

I'm a bit surprised by some of these answers to be honest. I can see it with a powerboat or probably a catamaran but surely its an extra risk factor for a sailing boat to have this big hole in the hull which is either underwater or potentially underwater when heeled, which cannot be shut off when motoring or maybe not at all, so you are totally dependent on the exhaust / through hull joint not failing?
My centre cockpit boat has the exhaust routed behind panelling through the aft cabin to exit at the stern. I did fit a carbon monoxide alarm in there, but otherwise, not a problem.
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Old 18-02-2021, 11:42   #18
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Re: Do you have an exhaust out the midship side?

We avoided all the issues of running the exhaust out the side midship by building a water/ gas separator for both the genset and the main engine. This lowers the back pressure to both engines and is very helpful if the run aft is long. If you have a turbo diesel it’s a big help.
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Old 18-02-2021, 12:28   #19
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Re: Do you have an exhaust out the midship side?

Our current boat's diesel generator exhausts out the side. Or previous boat's generator exhausted out of the transom.

Both are/were so quiet, I never could even hear them running. Never smelled the fumes from either one at anchor, but have smelled it when running both in the slip and no wind.
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Old 18-02-2021, 16:19   #20
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Re: Do you have an exhaust out the midship side?

Now for something a bit different.
In the early 1970's in Fremantle, Western Australia, i came across a ferro cement Herreshoff 55 sailed by a bunch of young chaps from NZ. As I recall it was the first ferro boat to circumnavigate. It had, as I recall, a Maori language name, possibly Aotearoa. NZ was then producing many ferro boats, mainly Hartley designs.

Besides being a very narrow boat it had some weird features: the main one being the engine which was placed well forward. The exhaust actually went up the aft mast. Obviously it was dry and cooled at that stage. I only saw the boat once on the hard so I know little about the details, but apparently it worked for them.

The chemistry of this arrangement would be a worry, but they may have had a steel sleeve or possibly the mast itself was steel.

I have no idea why they did it that way, but I suspect that the boat was very cheaply built by a bunch of keen young chaps who would try anything. They regaled me with stories about their adventures, particularly about running into a reef near Port Moresby and how well the boat managed the event. Apparently it was a very fast boat.
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Old 18-02-2021, 17:44   #21
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Re: Do you have an exhaust out the midship side?

In our experience we have lost two generators trying to exhaust out the transom.

In the first instance the exhaust hose ran down to above the keel and then up and out. It worked fine for many years, till we ran into very steep up and down seas. We think the pooled water in the low portion of the hose made it's way into the engine.

In the second instance, the water lift muffler was probably undersized, the exhaust hose above the water lift muffler had an inadequate top U, and the run to the transom was perhaps too horizontal and perhaps slightly sagging in regions. It's a long way to go and hard to get a slope. It didn't help that we toppled in Irma, raising stored water lift muffler water into the generator. Or so the current failure theory goes.

On the third try, the U in the exhaust above the muffler is more pronounced. the muffler is 130% oversized, and the "horizontal" portion is better supported.

There are good reasons for exhausting out the side. it's hard to meet all the criteria (1/2" per foot slope) on the way back there.
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Old 18-02-2021, 17:45   #22
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Re: Do you have an exhaust out the midship side?

Another centre cockpit with a midships engine exhaust but ours is actually underwater most times. We very occasionally get exhaust smells in the cockpit if the balance of wind direction, wind speed and boat speed all come together badly in a rare combination but it happens that infrequently that we don’t worry about it.

One place where it is a problem is in marinas if we have to charge batteries - the smoke/fumes are then more intrusive not only for us but for any boat in the adjacent berth. This is especially true in places like Vuda Marina in Fiji were moored boats are separated just by fenders.
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Old 18-02-2021, 18:10   #23
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Re: Do you have an exhaust out the midship side?

Very interesting to me, as I am struggling designing the exhaust for my 80HP diesel. It is located almost midships and it's a long run to the transom. Almost 6meters (19.5ft); from wet elbow to waterlock is 1m80, then straight up to goose neck is 1m20 and a slightly declining run to the transom of 3m10. I am very concerned about the back-pressure, and of where all the water is going to stay when engine is turned off. Maybe better to change the goose-neck for a gas-water separator and lead only the gas to the transom?
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Old 18-02-2021, 18:29   #24
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Re: Do you have an exhaust out the midship side?

Quote:
Originally Posted by auspain View Post
Thank you rslifkin for your reply, its a great help. We will be a 60 foot heavy displacement yacht for diving charters. If we ran the main engine out the sides and our generator out the transom, would you think this would be better for us with fumes or not enough odour to worry about?
Ran and owned dive charter boats in the past both power and sail, so you need to answer these variables before I could comment.

Main engine
Have you done back pressure calculations for both solutions?
Will you work off the stern boarding divers?
Will you use tender for drift dives or boat
Overnight or day charters?
Are you a power boat or sail?
If power, have you considered dry stack if fumes are your big concern?

Generaor
Assume continuous use for tank refill then look at exhaust water separator for quiet operation

https://www.cruisersforum.com/forums...st-228715.html
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Old 18-02-2021, 18:34   #25
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Re: Do you have an exhaust out the midship side?

Excellent input MV Caroline and SV__Grace both your inputs are helping tailor the discharge outlet plan for both Port and Starboard. The Northsea deign thankfully: GordMay shares on hear to people asking about midship exhaust has allowed me to do plenty of pre reading to understand the basics, have been missing the practical real-life experience you both have. Thank you kindly.
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Old 18-02-2021, 19:20   #26
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Re: Do you have an exhaust out the midship side?

All the replies have been excellent and I am very grateful for your time and input. The vessel is a steel 60' (18m) motorsailor ketch yacht and is currently 42 tonne when loaded 50. Building started around 1980 and was never finished by the builder and or launched. I have been working for the past few years making the required changes to meet commercial survey standards. An issue I ran into with the survey is running the exhaust under accommodation to the transom. If run through accommodation spaces the hose must be in a redundant gas tight housing. I was prepared to do this, however both the surveyor and a retired marine servicemen have said put it out the side. Which saves a lot! Except I have not been able to find anyone until now that had done it and was concerned about fumes on deck. The vessels engine room is mid ship under a bridge deck which makes up 1 of 3 watertight compartments. And if anything was to fail its defiantly in the engine room where I would like it to happen where its accessible.
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Old 18-02-2021, 19:23   #27
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Re: Do you have an exhaust out the midship side?

I wonder where the redundant housing requirement comes from. My exhausts run under the aft cabin to get to the transom with no special isolation from the surrounding bilge area. They are fiberglass tube rather than hose though, so I wonder if that matters.
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Old 18-02-2021, 19:34   #28
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Re: Do you have an exhaust out the midship side?

Quote:
Originally Posted by Pelagic View Post
Ran and owned dive charter boats in the past both power and sail, so you need to answer these variables before I could comment.

Main engine: Rolls Royce 12lt 190 hp 1800 Rpm max originally designed as a locomotive/tank engine,
Have you done back pressure calculations for both solutions? Not yet
Will you work off the stern boarding divers? To much rake on the stern and to high of the water 1.8m (6") we designed a sugar scoop transom addition but now going with a drop down aft side dive platform with ladder.
Will you use tender for drift dives or boat: 2 tenders small 3.4m run about 8 meter dive RIB
Overnight or day charters? All overnight
Are you a power boat or sail? Sail
If power, have you considered dry stack if fumes are your big concern? The engineering required at this stage would hold back the project to much

Generator
Assume continuous use for tank refill then look at exhaust water separator for quiet operation: Have separator for the genset thank you


https://www.cruisersforum.com/forums...st-228715.html
Its the start of the workday here in Western Australia I am working fulltime on both the yacht and refurbishing Bauer Compressors (cylinder fill) which help to pay for the work. I will check in again tonight to read and collate everyone valuable input. This has been so successful I will also put forward another issue following if I may.
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Old 18-02-2021, 19:37   #29
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Re: Do you have an exhaust out the midship side?

Quote:
Originally Posted by rslifkin View Post
I wonder where the redundant housing requirement comes from. My exhausts run under the aft cabin to get to the transom with no special isolation from the surrounding bilge area. They are fiberglass tube rather than hose though, so I wonder if that matters.
This is a requirement under the: Australian Maritime Safety Authority (AMSA) NSCV rules for a charter vessel = paying passengers. If it was for personal use this rule would not apply.
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Old 18-02-2021, 19:48   #30
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Re: Do you have an exhaust out the midship side?

Quote:
Originally Posted by auspain View Post
All the replies have been excellent and I am very grateful for your time and input. The vessel is a steel 60' (18m) motorsailor ketch yacht and is currently 42 tonne when loaded 50. Building started around 1980 and was never finished by the builder and or launched. I have been working for the past few years making the required changes to meet commercial survey standards. An issue I ran into with the survey is running the exhaust under accommodation to the transom. If run through accommodation spaces the hose must be in a redundant gas tight housing. I was prepared to do this, however both the surveyor and a retired marine servicemen have said put it out the side. Which saves a lot! Except I have not been able to find anyone until now that had done it and was concerned about fumes on deck. The vessels engine room is mid ship under a bridge deck which makes up 1 of 3 watertight compartments. And if anything was to fail its defiantly in the engine room where I would like it to happen where its accessible.
Sounds very much like my own steel motorsailor with the engine room midships under the pilothouse.
Main engine exhaust exits Port side fairly high up on shell as you can see on photo
10kw NL Gen on starboard side via a water separator... completely silent.

Keep everything in ER as then a raw water bypass leak under accomodation is never going to happen.

Rarely get exhaust smells in cockpits , but it does happen when speed and wind are about the same and exhaust just hangs.
That would be the same if exhausting out stern with a following breezeClick image for larger version

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