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» Forum Category: PT Boats of WWII
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» Forum Name: PT Boats - General
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» Topic:
Propeller Clearances for the 80' Eldo
http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?cid=101&fid=102&tid=4836
Last week, the polished bronze 3D printed propellers from Shapeways arrived and they look perfect (Dick, I'll send you the image to post here).
The question I have pertains to the correct clearance between the prop and the hull. If the prop is 30" in diameter, and the main wing strut drops down 16 5/8 inches, is 1 5/8 inches the correct prop/hull clearance?
It seems like the clearance should be more like 5 inches
Comments welcome
Best regards,
Greg Viggiano
GV
Posted By: Greg Viggiano | Posted on: Oct 13, 2019 - 1:18am
Total Posts: 14 | Joined: Oct 1, 2012 - 6:36am
The Elco prop shaft location drawings weren't much help, they don't directly give a clearance. I've scaled this Elco outboard profile to 10 pixels per inch so I could measure directly from it in my image program. Here's what I came up with:
Prop tip: 2.25 - 2.5 below keel
Posted By: Jeff D | Posted on: Oct 14, 2019 - 3:28am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Here are details from the Elco center prop shaft location drawing, courtesy of our fearless leader Dick Washichek:
Posted By: Jeff D | Posted on: Oct 14, 2019 - 3:35am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Thanks for the clarification Jeff -
That clearance seems to be what I have with the 28-inch center prop / strut combination, which is about .156" at 1:16 scale
The part that is confusing me is - with a scale 30-inch propeller (1.875) on the wing struts, and using the struts from Holden8702 scaled to about 16 inches, his struts are measuring about 1.0 inches, and I can't understand why am not getting sufficient clearance. It seems that the struts should be a little longer - around 1.100 inches
GV
Posted By: Greg Viggiano | Posted on: Oct 16, 2019 - 5:53am
Total Posts: 14 | Joined: Oct 1, 2012 - 6:36am
The Elco wing strut drawing shows the wing struts to be 16" from mounting flange to center of where the shaft would exit the strut so Holdens seems to be spot on. The mounting flange mahogany shim between the hull and strut would add about 5/8" more. The wing struts are mounted at right angles to the bottom, not plumb.
Posted By: Jeff D | Posted on: Oct 17, 2019 - 6:59am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Jeff;
Good point, Greg probably didn’t include the shim, an easy oversight for any modeler.
Take care
TED
Posted By: TED WALTHER | Posted on: Oct 17, 2019 - 9:07am
Total Posts: 3059 | Joined: Oct 16, 2006 - 7:42am
Thanks Jeff and Ted - I'll add the shim, but the clearance still seems too tight for a 30-inch scale prop with a 1.875 diameter. My math shows that there would only be a 1-inch prop-to-hull clearance (.0625 at 1:16).
GV
Posted By: Greg Viggiano | Posted on: Oct 18, 2019 - 7:26am
Total Posts: 14 | Joined: Oct 1, 2012 - 6:36am
Just the 16" strut and 5/8" shim minus the 15" blade give 1 5/8" clearance, plus a little more for the strut angle effectively lowering the tips. Dunno what to tell ya... you should be seeing a 1/10" clearance at least in 1/16" scale.
Posted By: Jeff D | Posted on: Oct 19, 2019 - 6:47am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
I don't have any info that the Elco ever used a 30in propeller. only much later did they increase from 28" to 29" (PT-613 series), according to my NARA documentation.
Posted By: Andy Small | Posted on: Oct 19, 2019 - 10:41am
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm
I see I have on my website that props were 28" center and 30" wing based on info from a now defunct website. I also see that Dick's Elco Parts Catalog lists 2 different props for each boat, center and wing... with no mention of the pitch or diameters. Andy, do you have any documentation mentioning that all 3 props were the same diameter? Also, the Elco drawings show a prop shaft for PT 545 that was 2.25" diameter as opposed to the standard 2". Do you know of any experiments with the 545 that might explain why the beefier shafts?
Posted By: Jeff D | Posted on: Oct 19, 2019 - 1:25pm
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Posted By: Andy Small | Posted on: Oct 19, 2019 - 2:05pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm
And here is the stuff when they increased the wheels to 29 on PT-613 class (direct drive boats). Includes comparison chart with older 28 wheels.
Posted By: Andy Small | Posted on: Oct 19, 2019 - 2:30pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm
And here is the prop info from the Nov 43 Miami Trials. Both Elcos with 28 inch wheels.
Posted By: Andy Small | Posted on: Oct 19, 2019 - 2:50pm
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm
Excellent, thank you Andy. I'm going to correct my page.
Posted By: Jeff D | Posted on: Oct 20, 2019 - 5:08am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
In the first letter I see the early 80' boats were supplied with a 30" for center and 28" on the wings? Was this order before they had a chance to test thoroughly and conclude straight 28's were the best?
Any idea of how the boats ran with the Elco Duchess D props? Another interesting bit...
Posted By: Jeff D | Posted on: Oct 20, 2019 - 6:19am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Sorry for the poor resolution on the first letter. Here you go, all 28 inch wheels.
Posted By: Andy Small | Posted on: Oct 20, 2019 - 11:25am
Total Posts: 262 | Joined: Nov 20, 2013 - 9:04pm
Hah that's funny, the 28s looked just like 30s. Thanks again Andy!
Posted By: Jeff D | Posted on: Oct 20, 2019 - 12:37pm
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Jeff,
So, you're saying the wing (outboard) prop shaft struts on the 80' Elcos kicked out to the sides, and weren't straight up-and-down?
Posted By: Drew Cook | Posted on: Oct 21, 2019 - 10:32am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am
The outboard struts on the ex-PT-486 were canted and matched the angle of the hull. The center strut was straight (although removed in these pictures). Here is a shot from 1984 with the newly installed 4 blade props (smoother than 3 blade).
This shot from 2017 shows the angle of the strut:
The shafts were off set from the rudders:
Former crew member of the Big Blue Sightseer ex-PT 486
Posted By: Gerry McGovern | Posted on: Oct 21, 2019 - 10:55am
Total Posts: 78 | Joined: Oct 7, 2016 - 1:47pm
Yep Drew, from Dick's DVD:
Posted By: Jeff D | Posted on: Oct 21, 2019 - 1:10pm
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Thanks Jeff and Gerry!
Posted By: Drew Cook | Posted on: Oct 22, 2019 - 11:02am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am
As a follow up to the discussion of Elco prop's and struts, it should be mentioned that the wing rudders on the Elco's were also perpendicular to the hull's bottom planking.
Larry
62 Bel-Air
260 Eagle EXP
79 Cole TR-2
2016 Corvette Z51
Posted By: bubbletop409 | Posted on: Oct 24, 2019 - 10:53am
Total Posts: 164 | Joined: Apr 22, 2013 - 11:48pm
Good point Larry! They were also 90 degrees to the base line in a side view, not 90 degrees to the slight upward angle of the bottom.
Posted By: Jeff D | Posted on: Oct 25, 2019 - 1:18am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
Since the last post concerned Elco rudders, am I correct in remembering someone saying the rudders were left unpainted, that they were natural metal (silver) in color?
Posted By: Drew Cook | Posted on: Oct 25, 2019 - 9:33am
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am
Yep unpainted manganese bronze. The spec manual for the later boats mentions a coating of lead / tin. Here's a thread discussing them Drew, Wayne mentions that several PT vets said they were a zinc color which would match up with the coating: [url]http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?fid=102&cid=101&tid=3893&sc=20&pg=1&x=0[/url]
Posted By: Jeff D | Posted on: Oct 26, 2019 - 5:52am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am
OK, Jeff, unpainted manganese bronze, zinc-colored.
So...what color would that be? Silver? Bronze?
Posted By: Drew Cook | Posted on: Oct 26, 2019 - 4:52pm
Total Posts: 1306 | Joined: Oct 19, 2006 - 10:44am
A dullish gray would be my guess, they don't seem to have much shine in B&W photos. But I really don't know.
Posted By: Jeff D | Posted on: Oct 27, 2019 - 7:01am
Total Posts: 2200 | Joined: Dec 21, 2006 - 1:30am