The PT Boat Forum

Forum Category: PT Boats of WWII

Forum Name: PT Boats - General

Topic: Turning radius question

I am looking for the minimum turning radius for an ELCO 80 at 40 knots.
I appreciate any info .
Thank you.

Posted By: JEno | Posted on: Apr 2, 2021 - 9:52am
Total Posts: 52 | Joined: Oct 13, 2019 - 9:52am

Hey JEno
I know that when I reviewed the PT658 Builders Acceptance Trials held on Lake Ponchartrain in New Orleans, one of the criteria they tested was the turning radius. I know what it is for a Higgins 78 foot PT boat but sorry not an Elco. But at least that may give you a place to start looking.

Also, The Boat may be running at 40 knots when it starts the turn, but it slows WAY DOWN (to something closer to 25 knots or even slower) when it is in the middle and end of the turn just due to physics. I know this from having been on PT658 and doing a high speed turn.

I just looked on Pages 64 and 65 of Dicks Transposed book, "An Administrative History Of PT Boats in WW2" (Recreated October 25, 2010 by the members of the PT Boat Message board) and found this in the Maneuverability Tests Section of the First Plywood Derby Section.

The pictures of the boats turning circles. Running at flank speed the boats made a full 360 degree turn, first to port, then to starboard. A blimp from the Naval Air Station at Lakehurst, New Jersey had been assigned to the tests. While the boats ran their circles, the blimp hovered above them and photographed circles, as represented by the wake. By considering altitude, focal plane length, and the size of the resultant print, the Photographic Laboratory at Lakehurst was able to compute the boats’ turning circles within two yards. Higgins 78 foot PT 69 turned the tightest circle to port- (against the direction of the revolution of the screws), PT 6’s turning diameter was shorter when the turning with the screws. This was probably due to the two Higgins rudders, large spade type affairs, which greatly abetted turns to starboard, as they presented a much greater thrust surface for the screws. PT 69 turned the port circle with a diameter of 336 yards, while PT 6 turned the starboard circle with a 256 yard diameter. Conversely, PT 69’s diameter for the starboard circle was 274 yards, while PT 6’s diameter for the port circle was 368 yards. PT 8’s turning circle to port- 443 yards- was the largest diameter recorded, although to starboard the boat turned inside the Elco entry, PT 20, by registering 340 yard to the Bayonne boats’ 382. PT 20’s 432 yard port circle gave it the worst average of all the boats. Once again this was no doubt due to the rudder arrangement, for Elco boats featured three small rudders, which made for easy, not close handling at high speeds.

In Review:
58ft Higgins for Dutch PT6 Port 368 Stbd 256
Higgins 78 ft PT69 Port 336 Stbd 274
77 foot Elco PT20 Port 432 Stbd 382
Phila Navy Yards PT8 Port 443 Stbd 340

Here is a video of PT658 in a HS turn you can watch: [url][/url]

I know there is no listing for an 80 foot Elco, but I would venture to guess that its numbers would be larger than the 77 foot Elco tested, PT20.

Jerry Gilmartin
PT658 Crewman
Portland OR

Posted By: Jerry Gilmartin | Posted on: Apr 2, 2021 - 4:44pm
Total Posts: 1307 | Joined: Oct 8, 2006 - 11:16pm

Thank you very much. That is exactly what I was looking for.

Posted By: JEno | Posted on: Apr 3, 2021 - 6:10am
Total Posts: 52 | Joined: Oct 13, 2019 - 9:52am