The PT Boat Forum
http://www.ptboatforum.com/cgi-bin/MB2/netboard.cgi

ť Forum Category: PT Boats of WWII
http://www.ptboatforum.com/cgi-bin/MB2/netboard.cgi?cid=101&fct=showf

ť Forum Name: PT Boats - General
http://www.ptboatforum.com/cgi-bin/MB2/netboard.cgi?fct=gotoforum&cid=101&fid=102

ť Topic: PT 761 Class
http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?cid=101&fid=102&tid=4369

While at the Naval War College last month, I found information leading me to believe that the PT 761 Class of Elco's were significantly different from the previous models as far as superstructure goes. The first image is my sketch of what the the day cabin and chart house (with raft)/cockpit configuration probably looked like. Bridge stretched across the boat and the cockpit area protected with aluminum armor. This area was slightly elevated above the boat's deck by about 6 inches. Don't have any info on the forward right .50 call tub other than it was farther aft. Other info mentions that these were going to be equipped with SO-5 radars (second image), most likely mounted on the top of the slope of the day cabin, so significantly higher that the previous mounting. Also, they were going to be equipped with W-100s. You can see a few superstructure similarities with PT809.

So, was wondering if anyone out there had any late war Elco plant images showing this final class of boats being built? Seems a shame that so little seems to be known of this final class of PTs.

PT 761 Class Sketch

SO-5 Radar

Posted By: Andy Small | Posted on: Mar 3, 2018 - 10:49am
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Guess there's not much out there? Here is the only photo I know of showing the forward chart house of PT767 (cropped from Chip Marshall's collection). You can really see the difference from the previous design. The two late 45 drawings showing the chart house and trunk cabin (day cabin) are from the Naval War College collection. Unfortunately don't have any photo of the starboard side. Hoping somebody has another Elco construction photo from the Aug-Sep 45 time frame.

PT 767

Elco Drawing 3580

Elco Drawing 3584

Posted By: Andy Small | Posted on: Mar 4, 2018 - 7:45pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Here's my first crack at the PT761 Class profile based on the data I've collected to date. I used portions of John Drain's PT 593 to expedite.

Posted By: Andy Small | Posted on: Apr 12, 2018 - 9:45pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Andy;
That is a good looking "first effort"!! To bad more can't come to light about this design modification, I hope you find more.
Take care,
TED

Posted By: TED WALTHER | Posted on: Apr 14, 2018 - 8:42pm
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am

Thanks Ted! Actually hit a good amount of pay dirt during my research visit this past week, but unfortunately no outboard profile drawings so I had to piece items together. Starboard, turret and trunk setup as well as most of the armament drawings were located. Engine room setup of the PT613 Class and PT761 were the same and seem to be configured to eventually use the W50 and W100s. Did locate the 761 plywood deck configuration and the plan view of the superstructure. Sensor information and location is only available through Elco/BuShips correspondence.

What I found interesting was that the 761 class drawings, for the most part, were dated earlier than the 613 class drawings. Looks like 761 class items were applied as mods to the 613 class as Elco/Navy looked to apply these items to production boats due to the end of the war and termination of the 761 build. Lastly, I like how the 761 shows the direct progression from all the original Elco PTs to the post war PT809.

Posted By: Andy Small | Posted on: Apr 15, 2018 - 11:01am
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Andy;
I hope you can post all this. You are correct, externally, I can see 767(761 Class) as the gap bridge between 613 class and the 809. It all makes sense now, I have always wondered where the 809 design originated, to me, it appeared to come out of thin air. She was at our pier at SBR-2 in 1991-92, Walking on her deck and looking at her, she was a real stretch from the 80 Elco design, I was familiar with.
Take care,
TED

Posted By: TED WALTHER | Posted on: Apr 15, 2018 - 4:24pm
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am

Frank posted some of Chip's photos of PT613 (National Archives) and I went ahead and did a comparison of the deck layout of the PT613 class from the previous factory weapons configuration. This was the same layout for the PT761 class. Thought it interesting that the forward turret doesn't have the cutout.

Also posted an update of my PT761 sketch.

Posted By: Andy Small | Posted on: Apr 23, 2018 - 8:32am
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Wonder if they were already flirting with the idea of a 40mm bow-mount, hence the weight shift aft...

Will

Posted By: Will Day | Posted on: Apr 23, 2018 - 1:40pm
Total Posts: 1955 | Joined: Oct 8, 2006 - 4:19pm

Will
That is a good possibility.
Andy;
As you noted most forward weight was shifted aft, including the torpedoes that are out of the photo. PT 613 was the first to have these modifications, and the remaining RON 42 boats. Good eye noticing that the ,50 mount doesn't have the indentation, I never noticed that on the last 10 boats, now I can see it, especially in the turn over photos of PT 620 (as ROKN PT 27), to the South Korean Navy in 1952.
Keep up the search!
Take care,
TED

Posted By: TED WALTHER | Posted on: Apr 23, 2018 - 3:42pm
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am

Might have found some info on the whole shifting the ordnance aft. A 2 Aug 45 Board of Inspection and Survey letter, subject: PT613 preliminary trials to the SecNav stated No more weight should be added to increase the trim by the head, as on starboard turns particularly at high speed, there is now a tendency to dip forward. I also was interested in the new 20mm location and it seems that was another hot topic with a request that the forward arrangement of weapons be re-studied and that the new position of the 20mm was now inadequate (too near side of vessel). Big problem with shifting stuff aft is it makes it hard for a boat to turn since you need the bow or a fin to build the turning moment. So in a 31 Oct 45 letter from the Supervisor of Navy Yard, NY, PT's 613, 616, 617, and 618 were to have a horizontal fin installed. I assume this would have been similar to the one installed on the Elco Planes boats such as PT487. This info was from the Naval War College Archives.

Posted By: Andy Small | Posted on: Apr 28, 2018 - 3:02pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Andy;
The stuff you are finding proves a thought I have always had, while the books say the ELCOPLANE died with the tests of PT 560-563 RON 29 Brooklyn to Miami, the info you are finding suggests the Navy told them to fix the problem, The speed an maneuverability were just too good to ignore. So they moved on to the ELCO SLIPPER(which was there version of trim tabs). I read in your previous research that PT 613 also sported new design rudders:

http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?st=10&nd=20&fid=102&cid=101&tid=3324&pg=4&sc=20

in this thread is also mention of a strake being installed on the keel somewhere between frames 20-35. I wonder if they were looking at a combination set up combining the aft rudders with what was termed a smaller bow rudder(which was actually on the keel amidships), as in the 1932 design of Miss America X.

The Irwin Chase Hydroplane boat diagrams of June 1911, that Jeff posted, were very interesting too. This diagram was the forerunner of the stepped hull design has been incorporated into the high speed offshore designs used by Cigarette, Fountain, Halter/USMI, Formula, Donzi, and many more,
Take care,
TED

Posted By: TED WALTHER | Posted on: Apr 29, 2018 - 10:49am
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am

Just an observation on the benefits of a stepped hull. I have a 26' Miami Vice style deep v speed boat with two small steps in it's bottom. The hull was originally designed without steps, some time later the design was changed to include the steps. The factory stated the speed of the boat with the steps increased by 5+ MPH all else being the same. In light of the fact the boats speed increased at any given RPM, I fail to understand why the PT's showed an excessive amount of fuel and oil consumption.

Larry
62 Bel-Air
260 Eagle EXP
79 Cole TR-2
2016 Corvette Z51

Posted By: bubbletop409 | Posted on: May 15, 2018 - 12:30pm
Total Posts: 164 | Joined: Apr 22, 2013 - 11:48pm

As a total guess, the design may have suffered from a lack of refinement Larry. The steps had a relatively steep straight angle that may have made it more difficult to push and keep up on plane. Here's what the steps looked like:

Posted By: Jeff D | Posted on: May 16, 2018 - 11:33am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

PT-487

[

Former crew member of the Big Blue Sightseer ex-PT 486

Posted By: mcgovern61 | Posted on: May 16, 2018 - 12:39pm
Total Posts: | Joined: Unregistered

Jeff, after looking at your illustration I can now see the major difference between the Elco steps, and the configuration of the modern day steps. Thanks for the info.

Larry
62 Bel-Air
260 Eagle EXP
79 Cole TR-2
2016 Corvette Z51

Posted By: bubbletop409 | Posted on: May 16, 2018 - 7:02pm
Total Posts: 164 | Joined: Apr 22, 2013 - 11:48pm

Did Elco boats before the PT761 class have the additional longitudinal bottom planking in the Fuel Tank Compartment (1/2 mahogany) and Lazarette (7/8 mahogany)?

Posted By: Andy Small | Posted on: Jun 6, 2018 - 8:39pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

It looks like it Andy, here's from a bottom blocking drawing for PT 163 and on courtesy of Dick Washichek. Section B-B is at frame 64-65:

Posted By: Jeff D | Posted on: Jun 7, 2018 - 2:51pm
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am

Completed drawing of PT-761 class. Weapons arrangement was supposed to be the same as that used by the PT-613 class, but I don't see how the 5inch rocket location would have worked. Radar is the SO-5. I included the Elco Slipper since they seem to have liked the adjustable kind since they were still on the boats (except PT-616) when they transferred them to the ROK.

Posted By: Andy Small | Posted on: Oct 19, 2019 - 3:00pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm

Andy;
Thanks! I like it, and this would make a great "What if" model of a RON 44 or RON 45 boat, (PT 766[:-grin-:],) if Operation Downfall ( Operation Olympic and Operation Coronet ) actually happened in 1945-1947.
Take care,
TED

Posted By: TED WALTHER | Posted on: Oct 19, 2019 - 3:43pm
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am

Very nice Andy, as far as I know it is a first! Thanks for the view of what they looked like. Hopefully you'll dig up some photos in your research trips.

Posted By: Jeff D | Posted on: Oct 20, 2019 - 5:17am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am