PT Boat Forum


Moderated by: Dick, Jeff D

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

Page: 1 of 1

Back to Topic Index Page 114 | Replies: 3

 Author  Topic: Torpedo firing sequence
rebsr52339

New Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Aug 22, 2012 - 6:29am
I have long loved the PTs and Subs of the "Big one" since I was a kid and heard stories from a PT Vet who served and lived in Waterbury Ct. I guess with this inquiry my retired anal Engineering background is kicking in. First if this has been covered before, I apologize and would appreciate knowing where it is located.
OK I am curious what the loading/electrical connection and firing sequence is for launching say a Mk XIII torpedo. How is this done? For instance, when the torpedo is first loaded in the rack is there a specific orientation it has to be in? Or, does the torpedo man connect a wire to it, which in turn, is connected to the bridge. Is the gyro angle set, pre-loading onto the boat or after? I am just curious what each member, Skipper and torpedo man, of the torpedo firing crews responsibility is and how does he carry out that responsibility.


REB

Total Posts: | Joined: Unregistered | 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: Aug 22, 2012 - 7:41pm
Hi Reb,

I will try to answer your questions one at a time. Jerry

What is the loading/electrical connection and firing sequence for launching a Mk XIII torpedo?

Loading is simple, connect a strap or a choker hitch in a sling to the torpedo for a crane to lift, and slowly lower into the rack. Attach the wire rope retainer straps and set the roll off cams up to prevent movement while moving launching lever forward to engage pins into cams. The straps are also engaged by these same pins. Load the torpedo with the warhead bolting ring approximately even with the forward strap. Connect the starting lanyard to the starting lever on the aft section. The other end of this lanyard can be connected to the rack itself or to a persons hand for manual starting. Otherwise the falling torpedo will pull the starting lanyard and lever. There are no electrical wires to connect. Torpedo is lauched by a hand signal from the bridge coupled with a solenoid push button, The two occur simultaneously. Pressing the button will energize a 24vdc solenoid magnet which pulls the launching lever that is also pulled by a crewman simultaneously.

In this PT309 photo you can see the rack with the cam operating lever and associated release gear


In this photo taken on PT309 in the Med you can see them lifting the Mk13 with a choker hitch in a wire rope sling from the crane.



In the photo you can see the two wire rope straps have their inboard end anchored to the rack. The other end is released by the pins operated by the hand operated lever



When the torpedo is first loaded in the rack is there a specific orientation it has to be in?

Since this is designed to be an aerial launched torpedo, it could enter the water in any orientation. However, there is definitely a top and a bottom to the torpedo. To achieve this, the bottom of the warhead has a 16 pound lead weight poured into its lower section. On top of that the molten TNT explosive mixture is literally poured into the empty shell while it is being held at a downward angle, which ends up solidifying at that angle which also tends to spread the weight toward the bottom. This helps to place the heavy side down when the torpedo enters the water. Several other parts, such as the exploder, the gyro, the depth control pendulum, the oil system and the majority of the crosshead gear assembly are also on the bottom. Also the control surfaces (rudder, depth planes) are all set up to work with the torpedo in the correct side up. So when they load the torpedo into the rack, they place the exploder side of the warhead on the bottom and the starting lever on the tail (along with depth setting mechanism) on the top.

Inside the photo you can see the bronze starting lever on the top of the aft cone shaped tail assembly the white turbine wheels and exhaust pipes the orange depth pendulum the silver gyro and the yellow crosshead gears oil pump and prop shaft and the black oil sump


Does the torpedo man connect a wire to it, which in turn, is connected to the bridge?

No, there is no electrical wire connected to the torpedo, only the lanyard for pulling the starting lever. The solenoid is part of the launching rack and is permanently wired to the pushbuttons on the bridge.

Is the gyro angle set, pre-loading onto the boat or after?

The gyro angles are pre-set when the fish is loaded into the rack per the gyro angle setting label plate on the foundation of the torpedo rack. On a Higgins boat, these angles are 2 degrees for the forward rack and 4 degrees for the aft racks. In this way, the 4 torpedos will go out and then turn back inward toward the heading of the boat and make a spread of 4 tracks that are about 100 feet apart. The crew of the boat almost never messes with the gyros on the torpedo except to install them at the point of loading.


What actions does the Skipper take to fire?

I am pretty sure he does two actions, and maybe they split it up into two people. One guy drives the boat (CO) while the other guy (XO) shoots the fish. To shoot, he raises his arm and presses the solenoid button at the same time he lowers his other arm. The arm signal is for the watching torpedoman standing at the launching rack who can pull the starting lanyard and then pull the launching lever. (Did you notice the Navy does this primary and backup method a lot?) It is a common theme on almost all ships I have ever been on. On the old powder actuated tubes there was a guy standing by the tube with a mallet to strike the primer cap to set off the charge in case the electrical signal failed.

In this builders photo of the PT631 Helm area you can see the 4 pushbutton box for launching torpedoes from the bridge


What actions does and torpedoman take to fire?
He stands by with the starting lanyard in his hand. Upon the signal from the XO he pulls the lanyard and then pulls the launching lever.

PT off Rendova fires practice shot, note torpedoman pulling lever.



PT309 fires practice shot note man is pulling lever to launch fish




PT171 fires torpedo at Borneo




Jerry Gilmartin

Total Posts: 1227 | Joined: Oct 8, 2006 - 11:16pm | IP Logged

rebsr52339

New Member
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Aug 23, 2012 - 3:19am
Jerry, you have cleared up about 65 years of curiosity and filled in the details. The Torpedo man and the lanyard was a big piece of the puzzle. I cannot thank you enough for your time, and patience. When I worked as a volunteer at a Tank museum for years, I was asked questations like these on a daily basis. The most often asked? You guessed it, "How do you drive one of these"? It was just plain fun educating the public and especially modelers.

REB

Total Posts: | Joined: Unregistered | IP Logged

Will Day

TOP BOSS
  

    
Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Will Day   Send Email To Will Day Posted on: Aug 23, 2012 - 10:58am
Much appreciated as always, Jerry!


Will

Total Posts: 1896 | Joined: Oct 8, 2006 - 4:19pm | IP Logged


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