PT Boat Forum


Moderated by: Dick, Jeff D

The PT Boat Forum ª PT Boats of WWII ª  PT Boats - General

Next Page » | Page: 1 of 2

« Back to Topic Index Page 11 | Replies: 11 | Pages: [1] 2

 Author  Topic: ELCO 80' mufflers
Bob Steinbrunn

Advanced Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Bob Steinbrunn   Send Email To Bob Steinbrunn Posted on: Jun 25, 2017 - 4:41pm
Okay, I've searched the forum and haven't found a specific answer to this, so please forgive me if it's been covered before:

Some photos show piping running from the transom to the mufflers just inboard of the butterfly valves. I see this in pics of PT 109, PT 117, and others. Al Ross shows this piping in his sketches in the instruction book for his 1/48 PT 103-196 series kit, and also in his sketch in ALLIED COASTAL FORCES OF WORLD WAR II, co-authored by John Lambert & Al Ross. (One does British, the other does American.)

Yet, many other photos show this piping to have been deleted. What is this? What's it for?

Al (I assume) writes in ACFOWWII in the Packard 4M-2500 Engine chapter:

"Sea water discharged from the salt water pump was circulated through the water jacketed exhaust manifold and then overboard through the exhaust pipe. On Types W9 and W10, the exhaust manifolds were cooled by fresh water from the engine cooling system. The modified centrifugal salt water pump had sufficient capacity for engine cooling needs and the salt water scoop merely directed the water to pipes or overboard with a sufficient quantity bypassed into the exhaust pipes to provide cooling of the exhaust gases, or dumbflow silencers."

So, the pipes (apparently) directed salt water to the mufflers. Can't have been good for the muffler cans...salt water corrosion and all.

Photos of PT 133 running into its mooring in the jungle show lots of spray exiting from the butterfly valves which are open, bypassing the mufflers. So, water it is.

The question is (after all this), what series of boats had this piping, and which did not? 103-196 had it? The rest did not?

And why do I ask? I have 3D-printed muffler parts with this piping for my 1/48 BlueJacket boat, and I'm doing PT 187. These pipes should stay? Should I cut them off?

Inquiring minds want to know.....



Cheers!
--Bob

Total Posts: 134 | Joined: Jan 23, 2016 - 9:16am | IP Logged

alross2

TOP BOSS
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of alross2   Send Email To alross2 Posted on: Jun 25, 2017 - 6:32pm
Based on the ELCO Parts Catalog and several ELCO drawings, it appears that the external cooling pipe was fitted to 103-145, 147-162.

Al


Total Posts: 993 | Joined: Oct 30, 2006 - 8:19pm | IP Logged

smallwi

Advanced Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of smallwi  Posted on: Jun 25, 2017 - 8:00pm
Bob,

I am not in a place where I can review references, but from memory I make the following comments:

The exhaust manifolds would have been cooled by circulating in an external jacket to the manifold. This would keep water out of the cylinders. The manifold is part of the engine and an expensive casting. While the exhaust pipes which bolt to the manifold are simple extrusions, an inexpensive part. The exhaust was cooled by direct injection of sea water into the exhaust. One of the byproducts of combustion is H2O, basically distilled water. This water would have diluted the salt content of the injected sea water, reducing the corrosive aspects of the sea water. I seem to recall the exhaust pipes were stainless steel which is resistant to salt corrosion, but I would need to validate the pipe material. All of the water exits with the exhaust, which is the spray you referenced in the photographs. None of this water would have gone into the mufflers, which were probably cooled by their direct immersion in the sea.

As for the piping, I recall seeing this and having the same question as you. I do not recall what I determined as the function. When I get back to references I will have to take a look again.

Cooling of mechanical devices is interesting design work. Some of the techniques used seem odd at first glance, but as you dig and understand the concepts/materials used it all makes sense from a mechanical design perspective. We all have to keep in mind the intended longevity of the device is also a factor. We have to remember that PT boats were not intended to have a long life. Corrosion by salt water over a long period of time would probably have been considered acceptable design tradeoff to weight and cost.

Bill

Bill Smallshaw

Total Posts: 130 | Joined: Jun 21, 2007 - 3:02pm | IP Logged

Daniele Klay

Advanced Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Daniele Klay  Posted on: Jun 26, 2017 - 7:12am
Hi Bob, note that if you've got mufflers with SW pipes you can't just cut the pipes off to convert to later standard. The mufflers were attached with flanges to the exhaust pipes on the earlier boats and with collars on the later boats (PT 163 and up). I you have interest I'll send you some reference material.
Greetings

Daniele Kläy

Total Posts: 126 | Joined: Jun 23, 2015 - 12:43pm | IP Logged

Bob Steinbrunn

Advanced Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Bob Steinbrunn   Send Email To Bob Steinbrunn Posted on: Jun 26, 2017 - 7:48am
A big "thank you" to Al, Bill, and Danielle: much appreciated! I believe Al answered my question as to which boats had the cooling pipes. Thanks Al!

And I agree with Bill that longevity may not have been a prime design criteria. Certain things are not expected to survive combat indefinitely. As a former combat helicopter pilot in Vietnam you might ask how I know this....

I have the ELCO parts catalog graciously provided on this site by Al as a downloadable pdf, and the drawings therein show the non-cooled mufflers, the butterfly valves, the clamps, and other hardware which will allow adding the proper muffler configuration to PT 187.

Like many modelers, I'm at the level where....if I can see it, I can make it.....but I have to be able to see it first. So, thanks again to Al for the ELCO catalog.


Cheers!
--Bob

Total Posts: 134 | Joined: Jan 23, 2016 - 9:16am | IP Logged

Jeff D

Moderator
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Jun 26, 2017 - 9:44am
As usual Al and Daniele have it right. And I think you too Bob, it's quite possible some water could blow out especially with the butterflys open. As far as I can tell the mufflers filled up quite a bit with water.

On PT 103-145 and 147-162 the water cooling jacket on the exhaust pipes ended before the transom. Thus the need for the separate jumper pipes. PT 103-138 had slightly different ones than 139-145 and 147-162's. PT 146 and 163 on carried the water jacketed exhaust pipes through the transom so there was no need for the external pipes.

The mufflers were mostly copper and bronze. From what I can tell the water went through a jacketed exhaust tube that housed the butterfly valve and into a water jacket attached to the side of the muffler. Then it passed through holes at the bottom of the jacket and into the exhaust inlet tube inside the muffler that had holes drilled at the bottom. Then the mix of water and exhaust (when the butterflys were closed) went up through the muffler body and out of the exhaust outlet tube that had holes drilled in the top.

Here's a view of a typical exhaust pipe section from Dick's Elco drawings. All the pipes were jacketed Bill, at least on the 80's. Interesting treatment of the surfaces exposed to salt water:





Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am | IP Logged

  Jerry Gilmartin

TOP BOSS
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jerry Gilmartin   Send Email To Jerry Gilmartin Posted on: Jun 26, 2017 - 6:16pm
Hey Bob,
Great question and interesting responses as well. Although the PT658 is a Higgins boat, they did use the same Packard engines as the Elco 80's. One detail that was mentioned I wanted to point out is untrue and is a common misconception. There was NEVER any seawater injected into the Exhaust pipes on Packard V12 Gas engines. The exhaust gas was purposely kept separated from the seawater by means of a "pipe within a pipe" arrangement. I am also fairly confident that these exhaust stacks as they were called, were made from copper and not stainless steel. This can easily be verified in the Elco Parts manual. The seawater leaving the Exhaust manifold connects to the Exhaust Stack outer piping (cooling jacket) and cools the stack from melting. At the other end of the stack, where it attaches to the transom via a "through hull" fitting, the sea water connects to the various muffler designs as defined in previous posts.

The misconception occurs because although seawater is commonly injected directly into the stack on numerous Diesel Engine powered boats, where it causes no problems, this isnt the case on V12 Packards.. This is because when you have a 100 octane gasoline powered engine like on a PT Boat, the exhaust temps coming out of the Exhaust manifold can reach temps in excess of 900F. (I know this from personal experience!) If you injected seawater into the inner exhaust pipe of that stack it would instantly flash to steam and cause excessive back pressure in the exhaust system, reducing engine power, possible vapor lock and liquid backflow into the pistons of the engine while cooling off after shutdown. Engine operating procedures for both Elco and Higgins boats that I have read take great precautions in ensuring the Exhaust stack outer cooling jackets are full of water before startup, and promptly drained after shutdown in order to prevent damage to the stacks or the engine exactly for this reason. If one melted it would allow the seawater to mix into the exhaust with disasterous results!

As far as the mufflers are concerned, what is said above seems correct from my sources as well.
I hope this is helpful!

Jerry Gilmartin
PT658 Crewman
Portland OR

Total Posts: 1469 | Joined: Oct 8, 2006 - 11:16pm | IP Logged

alross2

TOP BOSS
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of alross2   Send Email To alross2 Posted on: Jun 26, 2017 - 6:28pm
Quote:


Al (I assume) writes in ACFOWWII in the Packard 4M-2500 Engine chapter:





Nope, John wrote the Packard chapter.

Al


Total Posts: 993 | Joined: Oct 30, 2006 - 8:19pm | IP Logged

Bob Steinbrunn

Advanced Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Bob Steinbrunn   Send Email To Bob Steinbrunn Posted on: Jun 27, 2017 - 6:49am
Thanks for the info and drawing, Jeff. Much appreciated!

Thanks also to Jerry for the explanation. All of this esoterica is fascinating.

Cheers!
--Bob

Total Posts: 134 | Joined: Jan 23, 2016 - 9:16am | IP Logged

Bob Steinbrunn

Advanced Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Bob Steinbrunn   Send Email To Bob Steinbrunn Posted on: Jun 27, 2017 - 6:51am


Quote:
Nope, John wrote the Packard chapter.

Al





An easy mistake to make, Al. John Lambert writes almost as well as you do.



Cheers!
--Bob

Total Posts: 134 | Joined: Jan 23, 2016 - 9:16am | IP Logged

Next Page »

Pages: [1] 2


Lock Topic

 

Forum Legend

New Member

Reply to topic

More than 25 posts | Full Member

Reply to topic with quoted message

More than 50 posts | Advanced Member

Edit Message

More than 150 posts | MASTER

View profile

More than 300 posts | TOP BOSS

Email member