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View Full Version : Exhaust options with a forward-mounted small diesel?



cluttonfred
03-05-2016, 05:36 AM
I have mentioned before that I am fond of Atkin designs and have plans for Twilight (http://www.atkinboatplans.com/Sail/Twilight.html) (link), a 26' flat-bottom sloop with a cabin aft and a separate house forward over a head and an engine room on either side of the centerboard.

i know that some folks don't care for the offset forward engine placement but, sticking with the engine location as designed, what would be the best way to set up the exhaust? Off the top of my head, I see three options:

1) Wet exhaust all the way back to the stern alongside the prop shaft under the port bunk. Quietest, puts fumes aft, but potential fire or carbon monoxide danger if water pump fails.

2) Wet exhaust out the port side near the engine, or to a T connection and out both port and starboard sides North Sea style. Simplest, probably safest, but will brin exhaust back in your face in some conditions.

3) Dry exhaust to a stack on top of the low house, though there are some definite issues there in terms of fumes blowing aft to deck and snagging and/or burning the sails.

What do folks suggest?

Cheers,

Matthew

wizbang 13
03-05-2016, 06:08 AM
Air cooled or wet engine? (Your mention of water pump failure.......?)
Is the boat going to do a lot of motoring or only"in and out of the harbor"?

cluttonfred
03-05-2016, 06:56 AM
I have in mind a small Sabb single cylinder, water cooled. A keel cooler setup with no intake to clog is appealing, though then I'd need a separate raw water pump for a wet exhaust, so there would still be an intake to clog. So I guess that means keel cooler with draw exhaust or raw water cooling with wet exhaust. If it were an air-cooled Lister, that could be another argument for a dry exhaust. It's really a motorsailer so the engine would be used more often than not.

Figment
03-05-2016, 07:46 AM
Option 2, port side only, with a removable (installable) elbow to direct the exhaust downward and keep it away from the cockpit in most conditions.

Jamesh
03-05-2016, 09:21 AM
1) where you can see the exhaust and water coming out. An temp alarm will give to extra protection.
A small diesel will not need a large exhaust 11/2 water pipe might suffice? A engine mounted pump would be easy to rig.
James

Breakaway
03-05-2016, 09:54 AM
Option 2, port side only, with a removable (installable) elbow to direct the exhaust downward and keep it away from the cockpit in most conditions.

Seconded.

Option 1 is unsafe (CO)

Kevin

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rbgarr
03-05-2016, 11:21 AM
I'd feel safest with the North Sea style on a motor sailer.

Jamesh
03-05-2016, 12:10 PM
1) where you can see the exhaust and water coming out. An temp alarm will give to extra protection.
A small diesel will not need a large exhaust 11/2 water pipe might suffice? A engine mounted pump would be easy to rig.
James

cluttonfred
03-06-2016, 09:02 AM
Hmm, I was leaning towards no. 2, thanks. As this is a motorsailer and motor and sail power at the same time are likely, is a North Sea setup required to avoid submerging a port side outlet when heeled to port or is that a non-issue?

Ian McColgin
03-06-2016, 09:21 AM
That small and you can go dry right out the hull a bit above waterline. Just have the port with a goodly flange to act as a heat dump.

Jim Ledger
03-06-2016, 09:48 AM
That small and you can go dry right out the hull a bit above waterline. Just have the port with a goodly flange to act as a heat dump.


That's an interesting idea, Ian. Rubber hose after the manifold, or steel part of the way? How much louder would a Sabb sound without the water cooling, I wonder?

Ian McColgin
03-06-2016, 09:55 AM
LastBoat will have dry exhausts. Metal well wrapped in inuslation all the way. After the mufflers somewhat larger pipe to allow better heat dissipation. At the pipe to through hull that crinkle pipe that can handle the flex between engine vibration and the hull.

Breakaway
03-06-2016, 10:03 AM
That's an interesting idea, Ian. Rubber hose after the manifold, or steel part of the way? How much louder would a Sabb sound without the water cooling, I wonder?

Here's one for a listen: https://m.youtube.com/watch?v=YnwTdaZyqik

Kevin

Sent from my iPhone using Forum Runner

wizbang 13
03-06-2016, 12:10 PM
Oh they sound jusfine idling at the dock.
Rattle and shake yer bonesteethandnerves @ 5 knots they will.

cluttonfred
03-07-2016, 12:43 AM
Anyone have any thoughts on or experience with the port side only vs. North Sea (both sides) issue in a motorsailer?

wizbang 13
03-07-2016, 06:45 AM
No experience with that.
But I DID run a dry exhaust on an air cooled 16hp Ducati for 10 years.
It was no big deal to just add a 6 ' extension to the glass pack muffler to divert fumes downwind.
This was when I was young however, and was willing to stubbornly SAIL my boat. We ran the noise maker the absolute minimum.