Size and placement of exhaust funnels

[Totoro]

What is the logic behind today's placing of the engine's exhaust funnel on a modern warship? Some ships seem to have larger funnels compared to the power of their engines, some have smaller. Usually it's carriers which have unusally small funnels for the vast power of their installed powerplant. So, if they can get away with small, relatively narrow funnels then why do other warships (frigates, destroyers, etc) have relatively large funnels?

Also, how come some warships don't even have visible funnels? And we're talking about fairly large vessels, like the french Gowind corvettes? Those tout something they call waterline exhaust system. I'm assuming that has to have some drawbacks to it, otherwise all the other ships would use something similar, no? Does anyone know the logic behind using that unconventional exhaust placement? Is it applicable on other, larger ships and if not, why?

 

[kato]

Venting the exhaust at the waterline is specifically used with smaller vessels where the deckspace is needed for other purposes, often FACs, minesweepers or corvettes. Both topspace for masts, weapons etc, and of course also internally.

The obvious drawback is that at least part of the ship will constantly have smoke in the air around it, not exactly healthy; also, i guess the obscurement might be dangerous to e.g. helo ops.

A few designs - e.g. the Tarantul class - vent the exhaust at waterline at the stern of the ship for that reason; in other, more modern designs, the exhaust is often cooled with seawater or air before venting, which also of course lowers the IR signature of the vessel.

 

[Gollevainen]

Exhaust funnels are all down to the ships propulsion systems.

Naturally the ammount of boilers or diesels or gasturbines and their arragment determines how many funnels you have. The size of the funnels is also dependable on these factors.

Ships with no visible funnels at all are either nuclearpowered or all-diesel powered as the exhaust gases of marine diesel engines can be transfered from small pipes. Steam boilers needs alot bigger funnels. Gasturbines requires air-intake ducts which often are size and shapes of conventional funnels. Many gasturbine warships have rahter large funnels as the turbines itself can be changed via these funnels.

The gasturbine exhaust in Tarantul class is rahter interesting as the exhausts basicly works similary as jet engines giving additional thrust to the ship.

 

[AegisFC]

Flight 1, II's and most of the IIA Arleigh Burke class Destroyers have a system called BLISS (Boundary Layer Infrared Suppression System) that mixes the cooler outside air with the exhaust gases to help create an overall lower IR signature. If you look at a Burke you will notice its stack caps are larger than on a Tico, Spruance or Oliver Hazard Perry despite them all using the same gas turbines, the BLISS system is why.

 

[alexsa]

Exhaust funnels are all down to the ships propulsion systems.

Ships with no visible funnels at all are either nuclearpowered or all-diesel powered as the exhaust gases of marine diesel engines can be transfered from small pipes. .

Careful on making sweeping genralisations. "Small Pipes will only apply to smaller engine" and even catapiller high speed 1000 KVa gensets (which only butn MDO or MGO) have and exhaust diameter in the order of 200 to 300mm. Slow and medium speed diesels whichc can burn HFO genrally have a larger diameter.

In so far as propulsion is concnered the large slow speed 2 stroke diesel engines that power most commercial vessel require a siginficant exhaust diametre and the funnel space is utilised for a waste heat boiler/ economiser. The latter is necessary to heat the fuel (HFO) to a point it will run (about 80 degrees C) and for injection (about 140 degress C).

If you want an idea of how big these thing get have a look at the largest one currnetly in production.

http://gcaptain.com/maritime/blog/the-wartsila-sulzer-super-engine/the-worlds-largest-marine-diesel/

At 80000KW this is a very high output unit and the exhaust diameter will dwarf many Gas turbine exhausts

 

[isleofthanet]

Halifax class funnels

The HMCS Halifax class ships have an extremely large funnel (for the ships size) which has a cold air ventilation system with the gas turbine uptake fitted with a DRES (Defence Research Establishment Suffield) Ball and an open grating eductor. Which reduces IR signature significantly.

For more information see www.wrdavis.com/DRES.html.

Hope this helps

 

[Gollevainen]

Well I made the "generalisation" to point out that indeed the lack of visible funnels altogether can either be diesel powered or nuclear powered. I didn't state that all marine diesels have small diameter funnels however and as Alexsa pointed out the size of diesel funnels depends alot on the type of funnels used.

 

[alexsa]

Well I made the "generalisation" to point out that indeed the lack of visible funnels altogether can either be diesel powered or nuclear powered. I didn't state that all marine diesels have small diameter funnels however and as Alexsa pointed out the size of diesel funnels depends alot on the type of funnels used.

Noted and accpeted, however

as the exhaust gases of marine diesel engines can be transfered from small pipes

justiifed a response as it a rather emphatic statement.