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Forum Category: PT Boats of WWII
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Forum Name: PT Boats - General
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Topic: Elco Rudders
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OK, this might be an obvious issue here but one that has been bothering me for some time. As I sit here staring at my speed built 157, I'm wondering if anybody knows why Elco never increased the size of those tiny little rudders. I'm always reading and hearing stories about how the Higgins boats more more maneuverable and I must be missing something here. However, I must say that the aerial shot above that high speed 180 turn that Elco boat made in Newark Bay near the end of the Elco film is quite impressive.
Any thoughts?



Posted By: Roy Forbes | Posted on: Jul 1, 2013 - 6:13pm
Total Posts: 371 | Joined: Sep 5, 2012 - 4:57pm



Roy,
I am not an expert on these things but increasing rudder size does not automatically increase it's efficiency as other problems can be introduced such as drag, chattering/cavitation, and stress on the steering system. The shape and ratio of blade infront/ behind of the pivot is also important in high speed rudders.
I guess the engineers at Elco felt that they had made them as efficient as they could.


Best Regards,
Stu.






Posted By: Stuart Hurley | Posted on: Jul 2, 2013 - 1:14am
Total Posts: 247 | Joined: Mar 19, 2013 - 3:32am



Roy, don't forget that HIGGINS used only 2 Large Rudders, where ELCO used three small ones. They would have had to redesign the whole system. Elco boats used special pitched high speed props that would have also had to have been changed. I am sure engineers at Elco were always looking for ways to improve performance on the boats, trying to increase speed and engine performances. They were always looking for ways to keep the wake of the boats to a minimum, but with the high torque of the engines, they never found a way to do this. Somewhere, in my artifacts, I have a performance chart on the props. If I find it I will post it here. .............



Posted By: Frank Andruss | Posted on: Jul 2, 2013 - 1:29am
Total Posts: 3964 | Joined: Feb 9, 2007 - 11:41am



Roy;
Stuart and Frank are correct, the Elco rudders were place behind each propelller, therefore drag would play a factor in the size, also cavitation, and stress on the steering system would be created, if the prop remained the same but the rudder size was increased. Making the whole system less efficent (increase in fuel ,etc).
Take care,
TED.



Posted By: TED WALTHER | Posted on: Jul 2, 2013 - 6:25am
Total Posts: 2932 | Joined: Oct 16, 2006 - 7:42am




Roy;
Stuart and Frank are correct, the Elco rudders were place behind each propelller, therefore drag would play a factor in the size, also cavitation, and stress on the steering system would be created, if the prop remained the same but the rudder size was increased. Making the whole system less efficent (increase in fuel ,etc).
Take care,
TED.



Hi there.

Interestingly enough, you run into the exact same problem when building a scale radio-controlled model. The motors, prop shafts, props and rudders are designed as a balanced system. Chanhe the props or rudders size and you can introduce all sorts of problems. Even the amount a rudder is turned is limited b ecause after a certain number of degrees it stops acting as a turning device and works more as a brake which in turn puts a lot of load on the still reving motors which in turn causes them to overheat quickly.

As for the Higgins out turning the 80' Elcos, I think that is more a hull design issue than a rudder issue. If the Higgins only had two rudders but three running props that means that one of the rudders was not in line with a prop. Usually for maxinum rudder efficiency you want it aft of a prop so that the prop stream meets the rudder.

I recently put a very powerful motos into my 1/32 scale Lindberg PT boat that only has the original two kit rudders. Each rudder is aft of tthe wind motor. I have two really cheap hobby motors on the wing shafts. Interestingly enough, with just the high speed powerful center prop running thte turning radius of the model is a lot worse than it is if I run on just the two cheap hobby motors on the wing shafts.

Cheers from Peter

"Give me a fast boat for we want to get out of harm's way too."

Posted By: PeterTareBuilder2 | Posted on: Jul 2, 2013 - 6:46am
Total Posts: 204 | Joined: Dec 8, 2012 - 6:03pm



Thanks so much guys. Very interesting points. I can put that finally to rest, however, now you have opened another issue I can ponder. I have 3 nice large counter balanced rudders on the 623. A real pain to make but if I cut them down, will she run me efficiently?
And if not, mmmm, a bigger pain. Maybe I should leave things alone when all seems to be good.



Posted By: Roy Forbes | Posted on: Jul 2, 2013 - 12:30pm
Total Posts: 371 | Joined: Sep 5, 2012 - 4:57pm



The other guys have put their 2 cents worth in so I will do the same. A big thing for the Elcos were operating in the shallow waters. Maybe the shorter the rudder the better. Only a guess. By the way the kit rudders shape is a little off.



Posted By: Bob Butler | Posted on: Jul 2, 2013 - 1:50pm
Total Posts: 192 | Joined: Mar 23, 2013 - 11:58am



Bob;
I agree. But WOW, spoken like a TRUE steerable Elco Box fan!!!
Go Jerry Take your best shot!
Take care,
TED



Posted By: TED WALTHER | Posted on: Jul 2, 2013 - 5:26pm
Total Posts: 2932 | Joined: Oct 16, 2006 - 7:42am



Ted,
Fastest frontline PT boat was Higgins PT238 July 4th Race between 4 Squadrons based in Mindoro. ( I know Ron 16 and Ron20 were two of them) Close 2nd place
( by a mere 4 boat lengths) was a 77 foot Elco. They raced over a measured 10 mile straight line course and completed it in 8 minutes. That equals 75mph. Race rules specified full wartime weapons and fuel load and full crew on board. The Elco lost at least one of her engines during the race when they jumped a wave and the overspeed trip killed the ignition. Elco box my ass! Higgins Rule!

Peter, when you say "If the Higgins only had two rudders but three running props that means that one of the rudders was not in line with a prop."
I think you meant to say "that means each prop is not in line with a rudder". Because both of the Higgins Rudders are located directly in-line with each of the two outboard props. The center prop has no rudder associated with it. There is no rudder hanging out there all by itself. Just a clarification.

Have a Happy 4th of July everyone!
Jerry
PT658 HIGGINS




Jerry Gilmartin

Posted By: Jerry Gilmartin | Posted on: Jul 2, 2013 - 8:41pm
Total Posts: 1288 | Joined: Oct 8, 2006 - 11:16pm




Ted,
Fastest frontline PT boat was Higgins PT238 July 4th Race between 4 Squadrons based in Mindoro. ( I know Ron 16 and Ron20 were two of them) Close 2nd place
( by a mere 4 boat lengths) was a 77 foot Elco. They raced over a measured 10 mile straight line course and completed it in 8 minutes. That equals 75mph. Race rules specified full wartime weapons and fuel load and full crew on board. The Elco lost at least one of her engines during the race when they jumped a wave and the overspeed trip killed the ignition. Elco box my ass! Higgins Rule!

Peter, when you say "If the Higgins only had two rudders but three running props that means that one of the rudders was not in line with a prop."
I think you meant to say "that means each prop is not in line with a rudder". Because both of the Higgins Rudders are located directly in-line with each of the two outboard props. The center prop has no rudder associated with it. There is no rudder hanging out there all by itself. Just a clarification.

Have a Happy 4th of July everyone!
Jerry
PT658 HIGGINS




Jerry Gilmartin


Hi Jerry.

No, I meant what I wrote. One prop, the center one is not in line with a prop; just as yoy confirmed with different wording. ;<) I meant that the two outboard props on the Higgins boats were in line with the two outboard props but the center prop had no rudder aft of it. Apparently rudders work far better if they are in line with a prop. I guess thats because the prop condenses the water that flows to tthe rudder and being in line the rudder is exposed to tthe full force of that condensed water.

I think it would be really interesting to see what a center rudder (third rudder) in line with the center prop would do to increase the turning radius of a Higgins boat.

Cheers from Peter

"Give me a fast boat for we want to get out of harm's way too."

Posted By: PeterTareBuilder2 | Posted on: Jul 2, 2013 - 10:10pm
Total Posts: 204 | Joined: Dec 8, 2012 - 6:03pm



Jerry;
I knew you would like that one! That 77' Elco had to be PT 66 RON 8, she is the only one I know of that made it back to P.I. This was July 4, 1945 right? PT 66 was re-designated a small boat on Feb 23, 1945. Even though, her motor macs must have really loved the "Cheetah" to have her moving like that! I wish someone had actually filmed this race, it would be great to watch!
Take care,
TED
HAPPY 4TH OF JULY!!!!!!



Posted By: TED WALTHER | Posted on: Jul 3, 2013 - 6:17pm
Total Posts: 2932 | Joined: Oct 16, 2006 - 7:42am



Roy, my PT-157 model has three motors/shafts/props and when running it throws up the identical rooster tail and 'trough' behind the fantail (stern) when running at higher speeds such as I see in still photos and film of PTs of the period. It evens has the pronounced yaw when running in reverse as noted by skipper in an article a read some time ago..

I can say that given the running characteristics of my PT-157 very closely (if not exactly) emulates the those of the full scale boat, the rudders provide ample maneuverability. It surprised me as as well considering their smallish size however whether be the total square inches of area (when all three rudders are added together) or the rudders' placement right in back of the props or maybe even both, it is fine. I'm not aware of any complaints by Skipper Liebenow of the 157, of maneuverability in this regard but will ask the next time I speak with him.

To the point that the rudders maybe were shorter as they patrolled hallow waters, the props were about another 12 to 14 lower then the bottom of the rudders so I don't think that was a design limitation and even here the center prop/rudder were much lower then the outer props/rudders.

[b]The PT-157 model emulates the full size version in maneuverability very well....[/b]
[IMAGE]http://i130.photobucket.com/albums/p249/ptboats/Bridge%20Carney/I-WLseries1frameunksoonafter131248.png[/IMAGE]

Posted By: TheBridge | Posted on: Jul 5, 2013 - 3:43pm
Total Posts: 302 | Joined: Nov 22, 2009 - 3:04pm



I am currently doing a scratch build of a 1/16th scale 85' Air Sea Rescue Boat from plans drawn by Al Ross. These boats were very similar to the 80' Elcos in general hull shape and powered by two Packards. The rudder size and shape are also similar to the Elcos, however while the props were located 45 inches outboard from hull center line, the rudders were much farther apart being 64 inches outboard from center line.

I wonder what the reason was for such an un-conventional setup, and what if any benefits were derived from that arrangement?

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

Posted By: bubbletop409 | Posted on: Jul 10, 2013 - 11:29pm
Total Posts: 164 | Joined: Apr 22, 2013 - 11:48pm