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| Tony's Tips |
ARTICLE DATE: 10/01/2006 |
| Marine Exhaust Systems |
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| Dry Exhaust Designs and Ideas |
| Dry exhaust systems are not very common in the typical
marine vessel used in recreational service. There are many reasons why you
do not see them although, in many cases, they do have desirable features when
designed and installed correctly. A dry exhaust system can add considerable
costs, is usually more complex as to proper design, fabrication and installation,
and can be a dangerous fire hazard if the design and installation is not 100%.
What many operators and builders DO NOT understand is the approx 1/3 of the
total energy (heat) that comes from the fuel that is consumed by a diesel engine
is expelled as heat thru the exhaust system, and this heat must be contained
and then exit the vessel safely. With a water cooled exhaust (wet systems),
controlling and dissipating this heat is much simpler. |
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| Commercial
Fishing Vessel "Ocean Pearl" - Images above show shop construction, layout,
and pre-assembly is time consuming but it's the only way. This "dry system"
took about 60 man hours to design and fabricate. Images below show support
brackets and installation. The under deck installaion took about 2 hours. |
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When looking at the pictures of dry exhaust systems, a
few of the common design & installation features that you may notice are:
1) The use of stainless steel through-out the system when practical. 304L &
316L series stainless allow the use of lighter weight sections because it is
not subject to the corrosion effects of diesel exhaust on the inside or corrosion
on the outside from salt laden air. SS can operate at the continuous temperatures
in the 700F to 1300 F range that diesel engines exhaust produce without losing
strength or scaling. SS can tolerate these high temperatures without being
cooled by large external air flows that trucks and other non-marine applications
have. |
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| Commercial
Fishing Vessel "Saint Peter" - 28 Ft lobster vessel powered w/ a Cummins
QSB. Images above - we had limited space but worked around what we had.
We only had to "wrap" under the deck because of proper "drafting" of the
muffler compartment. Images below show lower muffler support and our "unique"
type of muffler supports that not only give a lot of adjustability but transfer
close to zero heat to the nearby attachment surfaces. "Top hat" and upper
stack that employs the same features. Expensive and time consuming to design
and fabricate, but this is one place you DO NOT want to cut any corners. |
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2) Un-cooled exhaust piping "moves" or expands and the
use of flexible "bellows" is mandatory. We use SS bellow made of 321 SS at
it has shown to give long term reliable service in demanding high hour commercial
application.
3) Under the deck is where most care must be taken as to spacing and supporting
or "hanging" the system. You must allow enough space to install proper
insulating blankets or covers and all support brackets must allow a minimum
of heat transfer to the adjoining surfaces. |
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| Cummins
N-14 in the 75 Ft commercial seiner "Anthony G" with 5" dry outlet to 6"
bellows and muffler. |
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4) Once the exhaust exits the deck and is now in the typical
"muffler" compartment above the deck, the use of natural "drafting"
from the heat is critical to safety. Ever wondered why the stacks on ocean
liners are so large on the outside? That's because they use the heat that goes
out the exhaust to "draft" the internal piping and engine room - just like
a chimney, the heat draws excess air thru it.
5) Dry mufflers are large, heavy, can be quite cumbersome to deal with, and
get extremely hot. The bracketing to hold and support a muffler on a vessel
must not only be strong, it also must not transfer heat to the surrounding
support surfaces. We always leave plenty of room in this area and allow the
use of draft air to cool the support brackets. If the muffler compartment is
large enough and well drafted, then using an insulating blanket around it is
not necessary as the draft air becomes the insulator. But since each design
is different, this is now an option based upon the uniqueness of the overall
installation. |
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| Cummins QSC w/ entire dry run and muffler support "on-engine". |
Simple John Deere 99 Kw generator and attachment to existing "under the deck" dry muffler - Installed on the 90 Ft, 300 Ton commercial long liner "Ventura II". |
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| Hopefully if you are going dry, some of
the designs and ideas we employ will help you build a safe and well constructed
system. |
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