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 Author  Topic: MAX and CRUISING SPEEDS
Frank J Andruss Sr

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Frank J Andruss Sr   Send Email To Frank J Andruss Sr Posted on: Jun 9, 2010 - 1:53am
I have had some interesting coversations about the range of the PT Boats during the War. I have found several different answrers. What was the actual cruisng speed of the Elco and Higgins PT Boats, and what was the actual range of those boats at Crusing speed. What did the boats consume in fuel for the 77 footers vs the 80 footers in 1945 at cruisng speeds. Was it different for the Higgins PT Boats?


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BobPic

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Jun 9, 2010 - 5:55am
I have had many arguments about PT speed. Anyone who has navigated a boat by dead reconing knows that accurate knowledge of the speed. fuel consumption and course is fundamental. Al l we had to determine speed was the RPM guage. In Melville we trained using speed values selected by the instructors. When I first went aboard the 167 in Tulagi, there was no speed vs RPM curve. I protested as violently as a new QM could, and our exec Red Faye, got me permission to trace a speed/rpm curve from squadron secret files. Speed and fuel consumption of the PTs was a closely guarded secret, even tho such info was vital for safe navigation and patrol plans. For each patrol cruising speeds were chosen depending on the assignment but usually were near 40 knots. At that speed we assumed fuel was consumed by the three engines at a rate of about 300 gal/hr. (probably a little high). If you assume usable fuel (less safety reserve) was 2500 gallons, then the max range was half of 8 hrs at 40 knots or 160 miles. Slower speeds or slow patrolling on sight extended the range. Each patrol was carefully planned with fuel consumption in mind.
I understood the Higgins, being "chunkier" was slightly less efficient and the Huckins was worst.




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Frank J Andruss Sr

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Frank J Andruss Sr   Send Email To Frank J Andruss Sr Posted on: Jun 9, 2010 - 6:58am
Thanks Bob, that does help although I understood cruising speed was anywhere from 25 to 35 , giving the boats roughly 259 miles during the 12 hour patrols. I bet we get many different answrers on this one.


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Jeff D

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Jun 9, 2010 - 7:13am
Interesting Bob, I guess that they didn't want the enemy to know how fast and how far the range was. The hnsa site has some data for the 77' boats, it looks real close to your estimate for the 80' boats:

http://www.hnsa.org/doc/pt/doctrine/part6.htm#pg95

You have a heck of a memory!



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BobPic

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Jun 9, 2010 - 7:36am
Just one more comment: The definition of cruising speed does not generally mean the average or typical speed on patrol. The cruising speed of a boat or plane usually means the speed specified for safe sustained operation with minimum stress on the system. We usually left base so as to reach our patrol area at a more leisurely speed for the comfort of the crew.


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TheBridge

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of TheBridge  Posted on: Jun 9, 2010 - 9:29am
Bob - what was the cruising speed in terms of RPMs? I'm guessing about 1400 RPMs?

I think I've heard the desired speed when launching a torpedo (from the tubes that is) was about 28 knots? (which is the speed of the torpedo when it travels in the water)

Bridge


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BobPic

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Jun 9, 2010 - 9:51am
I don't have good info on this. I believe the cruising speed was somewhat higher than 1400 rpm, but a number escapes me. It was well below the red line of max speed. The cruising speed number was academic and was not of general interest. Torpedo launch speed was taught as though you used the provided torpedo sight, which was a farce. It was a maple stick contraption that looked like a broken deck chair. You were supposed to set the estimated target speed and direction by thumbscrews on graduated maple bars, then set the torpedo speed and the boat speed on other bars, then look thru the sight at the target which gave you the proper lead. This was all impossible in total darkness and supposed the target would not change speed or direction when he heard your engines rev up. You would not want to set the boat speed at the torpedo speed or you might run into your own torpedo as you turn.
We launched torpedoes by the seat of our pants. We kept on a collision course with the target and changed as he manouvered. We ran in to what many called point blank range and launched the torpedo and RAN.
Our score was not good and it was difficult to even know how the launch turned out if there was a big battle going on. By late 44 torpedo attacks were rare and the guns were our main weapons.


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