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ť Forum Name: PT Boats - General
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ť Topic: Patrolling with Engines Muffled
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Guestion:

If a PT boat captain is patrolling with the engines muffled, is the exhaust being routed through the mufflers or are the mufflers cut away and the exhaust is being routed to the exhaust ports below the surface of the water?

I should think that the boat would run more quiet if the exhaust is being routed to the exhaust ports below the surface of the water, especially at low speeds across the water, such as would be used on most patrols- maybe 15 knots and under.

So, am I wrong to assume that when the boat is running muffled, it is sending the exhaust to the ports below the surface and NOT thorugh the mufflers?

Allan

Posted By: Allan | Posted on: Feb 28, 2009 - 8:23am
Total Posts: 161 | Joined: Sep 18, 2007 - 7:07pm

There may be a misconception here. The exhaust pipes (6) with the butterflies open (horizontal) let the gasses flow straight out. VERY LOUD. When the butterflies were closed, the gasses and noise were diverted downward through the mufflers and into the water. The resulting noise was diminished greatly but was still significant to one who knew what to listen for. However, ot sounded a lot like surf and not too noticable. We could not advance the throttle at all with the mufflers on, so our top speed in that condition was 6-8 knots.

Posted By: BobPic | Posted on: Feb 28, 2009 - 9:27am
Total Posts: | Joined: Unregistered

Just to add a little more information, the mufflers were open when starting the engines.

Posted By: QM | Posted on: Feb 28, 2009 - 9:58am
Total Posts: | Joined: Unregistered

So, to hash over an old, old point....

It would have been next to impossible for PT 109, idling muffled at 6 to 8 knots, to get out of the way of the cannonballing Amagiri, steaming along at 30-plus knots, coming out of the blackness -- in 10 seconds...

No wonder the 109 was rammed.

Posted By: Drew Cook | Posted on: Mar 1, 2009 - 4:30am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am

I thank you, Gentlemen. That, indeed, resolves my issue.

Allan

Posted By: Allan | Posted on: Mar 1, 2009 - 6:06am
Total Posts: 161 | Joined: Sep 18, 2007 - 7:07pm

I had the pleasure of having a three way conversation on the phone on Friday with 2 guys who were on PT 162. The XO of the boat, who was there that night was Sam Reynolds, and Russ Pullano who came after. Sam and Russ both agreed that the 10 to 12 seconds needed to get out of the way, was no where near enough time with 2 wing engines, running, but in Neutral. Remember, this was standard practice in those days to run on the center screw as it was deepr in the water, and produced less wake. The big quaestion I had for Sam was why they never went back. His reply "We thought no one could have lived through that explosion". Sam said the fires caused by the explosion had died down very quickly, making it almost impossible to have found anyone in the area on one of the darkest nights he had seen.

Posted By: Frank J Andruss Sr | Posted on: Mar 1, 2009 - 8:22am
Total Posts: 3497 | Joined: Oct 9, 2006 - 6:09am

Frank; I'm not disputing anything you say and I have great respect for your sources, but let me argue a little about low speed patrolling . It was indeed a practice to patrol with only the center engine. However we conducted tests and found that there was no discernable effect due to the prop being deeper.The main reason to use the center engine was that its thrust was along the keel. Either outbourd engine alone produced a torque that had to be compensated for by using a little rudder. Then the combination of off-center thrust and rudder would reduce the speed (usually not significant) but the boat would be forced sideways slightly from the apparent course ( compass heading) .
As to wake, we were not so concerned with the wake as we were the rooster tail (which contributed to the wake). We made only subjective judgement tests, but no one could tell the difference at any specific speed regardless of the engine configuration.

Posted By: BobPic | Posted on: Mar 1, 2009 - 10:16am
Total Posts: | Joined: Unregistered

Bob

Thanks very much for your take on the wake and center engine theory. I had been told many times from different Skippers that this was their practice to keep wake to a minimum. I guess even the smallest wake can be seen from Jap Float Planes, which is exactly what happened to PT 162, when they dropped a daisey cutter on them, killing one and wounding another.

Posted By: Frank J Andruss Sr | Posted on: Mar 1, 2009 - 2:32pm
Total Posts: 3497 | Joined: Oct 9, 2006 - 6:09am

...And just to add to this, a Jap float plane had also dropped a bomb off the port beam of the 109 while on patrol on July 19, 1943, which slightly wounded Maurice Kowal and Leon Drawdy, and riddled the boat with shrapnel, including bashing "an ugly dent...in the metal splinter shield that ran...along the port side of the cockpit beside the wheel."

Posted By: Drew Cook | Posted on: Mar 2, 2009 - 5:21am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am