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» Forum Name: PT Boats - General
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» Topic: Question for PT Boat Experts
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I have enclosed two pictures with some sort of "fins" on the side of the boat. One picture show a pt boat with the "fins" on and the other it seems they took them off but they were there. Can anyone tell me what they are? And what they are used for? Thanks

[image]http://i130.photobucket.com/albums/p249/ptboats/Victor%20Chun/ptboatfin2-SMALL.jpg[/image]

The previous photo in this place was substituted for a smaller version to be more down-loading friendly, - To see original full size image click here:
[url]http://s130.photobucket.com/albums/p249/ptboats/Victor%20Chun/?action=view¤t=ptboatfin2.jpg[/url]



[image]http://i130.photobucket.com/albums/p249/ptboats/Victor%20Chun/ptboatfin1-SMALL.jpg[/image]

The previous photo in this place was substituted for a smaller version to be more down-loading friendly, - To see original full size image click here:
[url]http://s130.photobucket.com/albums/p249/ptboats/Victor%20Chun/?action=view¤t=ptboatfin1.jpg[/url]


Victor K Chun

Posted By: victorkchun | Posted on: Dec 25, 2008 - 4:32pm
Total Posts: | Joined: Unregistered



I will try a wild guess. First, the pictures appear to be two different boats. If I am identifying what is referred to as fins, it may be a variation of part of the cradles supporting the boats.

Posted By: QM | Posted on: Dec 25, 2008 - 5:42pm
Total Posts: | Joined: Unregistered



I read that was called the Elco Step.



Posted By: SouthWestPacificPT | Posted on: Dec 25, 2008 - 5:52pm
Total Posts: | Joined: Unregistered



Hi Victor, I see that in your first photo there are six vanes or fences attatched to the side of the boat, did you also note that there appears to be a corresponding angle fittered to the underside as well ? It is of interest to see a fixed form of the Elco slipper fitted to the rear of the boat with another angled plate fitted to it to. This plate has been fitted over the rudders with large cutouts to allow the rudders to turn. The chine also shows reinforcement that goes all the way to the end of the slipper

I use the term Slipper as i have your book and am looking at it on page 82 and this term fits.

In your second photo the side vanes are gone but the rest remain the boats do look differant but the lower one looks to have been in the water a little longer than the first. The lower photo also shows the added items better and is a clearer photo.However i would think that the reason the side vanes are missing is not that they have been taken of rather the boat has removed them due to high speed and manoeuvrs.

Now to what they may be, knowing that Elco tried various ways to increase the boats speed i would suggest they are an attempt at that.



D.buck

Posted By: David Buck | Posted on: Dec 26, 2008 - 4:17am
Total Posts: 332 | Joined: May 4, 2008 - 2:59am



Victor;
The top photo is PT 562 RON 29( notice chalk marking on cradle portion aft, "PT 562"). The bottom photo is of PT 487 RON 4( notice numbers on engineroom hatch, even though cradle is marked PT 562). Both these photos were taken around December 16, 1943. The photos were taken at ELCO. In the 487 photo look closer, the "steps on the side are not removed, thats how the look from the rear port quarter.
With this installed PT 487 was clocked at 55.95 knots(almost 65 MPH) with a light load and 53.62 knots with full warload.
The six steps are installed port and starboard and the plane is on the stern. I am just guessing but on Giant Killers you see a boat in Bayonne Bay from an aerial film shot turn around at high speed, I would be willing to bet that is 487 with this installed, the boat was recorded at high speed turn and reversing course in 6 seconds.
In the PT 562 photo the boats of RON 29 were painted in measure 31/5P for thier shakedown period. Then painted Thayer Blue for deployment to Med.
Anyway this was installed on PT 560-563 of RON 29 and the 4 boats ran fromm New York to Miami. This test run showed 25% more fuel was used, 75% more lubricating oil was used at cruising speeds. In heavy seas the boats rooted in heavy seas, steering was lousy, and acceleration dropped. The steps warpped and the brackets became loose and cracked, the boats also became sensitive to added weights. In other words this worked great in calm seas only. See page 78 in "AT CLOSE QUARTERS".
Take care,
TED



Posted By: TED WALTHER | Posted on: Dec 26, 2008 - 7:33am
Total Posts: 2837 | Joined: Oct 16, 2006 - 7:42am



Or, could it be something that Elco used to stabilize the hulls when they flipped them right side up after being upside down during the construction and they hadn't been removed yet?

Just thinking outloud ...





Posted By: TGConnelly | Posted on: Dec 26, 2008 - 7:44am
Total Posts: | Joined: Unregistered



Nope, it is the ELCOPLANE.
take care,
TED



Posted By: TED WALTHER | Posted on: Dec 26, 2008 - 8:20am
Total Posts: 2837 | Joined: Oct 16, 2006 - 7:42am



There's some nice detail of the "stabilizers" attached to the cradel as well for Frank's crane project.

Very interesting photos Victor. Thanks for sharing.
Dave

David Waples

Posted By: David Waples | Posted on: Dec 26, 2008 - 8:37am
Total Posts: 1569 | Joined: Jan 2, 2007 - 9:55pm



I don't think they're gone in the 2nd photo, just a trick of the photo's exposure. Looking at the chine you can see them.

My inexpert, total guess is vents that possibly lead to the ends of the steps, maybe to introduce air behind the steps/under the hull to reduce drag.

The stepped hull vee is not dead, check out this sexy babe:
[url]http://www.floridamariner.com/wcms/content/134.php[/url]




Posted By: Jeff D | Posted on: Dec 26, 2008 - 8:55pm
Total Posts: 1665 | Joined: Dec 21, 2006 - 1:30am



Ted is correct. This was the six step process that was the ELCO PLANE, a trial of attached steps on bothe sides of the Hull. This trial made for an incredible increase in speed, but the boat handled sloppy at those speeds, and the increase in lube consumption and fuel was a disaster, not to mention the steps rotting off the boat or breaking off. It was dis-continued............



Posted By: Frank J Andruss Sr | Posted on: Dec 27, 2008 - 12:10am
Total Posts: 3138 | Joined: Oct 9, 2006 - 6:09am



Thank you for setting me straight ...

Garth



Posted By: TGConnelly | Posted on: Dec 27, 2008 - 9:53am
Total Posts: | Joined: Unregistered



I think they thought it would get the boat up and plane quicker.

Ray


Posted By: Ray Wilbur | Posted on: Dec 27, 2008 - 1:32pm
Total Posts: | Joined: Unregistered



Hi Ted,
This is the first time I post on message board. I hope you get it ok.
Thank you Ted for your answer, especially how you indendified the boats.
The steps as mentioned in your answer were called louvres according tto Elco's note on the back of the original photo. I think the louvres were
part of the Elcoplane system. The steps were fitted to the bottom of the
boat. Six of them can barely be seen below the louvres in the second picture of PT 487. The purpose of these steps was to help lift the hull
further out ofthe water thus reducing drag and increase speed. However,
can you explain how the louvres help the system reduce drag. Jeff D
mentioned in his answer about introducing air behind the steps under
the hull to reduce drag. Do you think the louvres have anything to do
with that? If so, how does it work?
Happy New Year and smooth sailing.
Victor

Victor K Chun

Posted By: victorkchun | Posted on: Dec 30, 2008 - 10:40am
Total Posts: | Joined: Unregistered



Hi, Victor the idea behind the Elcoplane was to take advantage of the stepped hull design. This has the effect of creating an area under the hull that rides on a layer of air bubbles, these bubbles lower the boats surface tension or drag thereby allowing the boat to achive higher speeds with less power/effot. The idea of bolting the steps/louves on to the hull was so that a new hull design did not have to be made during wartime production.
For further info and to see drawings of Vospers approch to the same idea see page 58 and 59 of Allied Coastal Forces of World war 11 by John Lambert and Al Ross.
By the way the Vosper idea did not make it to a fighting boat either the trial boat ending up target towing after trials, but it is interesting to note that only two engines were fitted and she was quite fast with those two.

Cheers David.

D.buck

Posted By: David Buck | Posted on: Jan 6, 2009 - 3:22am
Total Posts: 332 | Joined: May 4, 2008 - 2:59am



Hi David,
Based on your reply I concluded that the 6 louvres on the sides of the boat are sir intakes that provide air to the bottom of the boat as a layer
of air bubbles to lower the boat's surface tension or drag. If that's the
case, how did the air get from the louvres to bottom of the boat? Was
a fan or compressor uaed? I don't think the speed of the boat can
push the air down, for the openings of the louvres seem to be facing aft. Any idea?
Thank you for all the help.
Victor



Victor K Chun

Posted By: victorkchun | Posted on: Jan 6, 2009 - 10:14pm
Total Posts: | Joined: Unregistered



Hi guys, just adding my two cents into the discussion,

Its my hunch, and hunch only, the items referred to as louvers are merely foils used to smoothly divert the water from the flat face of each of the haul brackets used to attach each plane step, hence reducing drag from structural components. If I recall correctly, somewhere in “At Close Quarters” there was a mention of the ELCO Planes as being five or six separate steps attached o the boom and to the sides of the boats with brackets. If my assumption and recall is correct, Photo 2 shows the unprotected metal brackets running down the side wall of the boat to the edge of plane step which is flush with the Chine. With photo 1 showing the louvers (Foils) in place. Also at any high speed the ELCO 80 footer haul would naturally begin to plane and lift itself out of water, where at least the first few louvers would be out of the water and have no effect whatsoever.

OR

I could be completely wrong!

All the best,
Dick . . . .





Posted By: Dick | Posted on: Jan 6, 2009 - 11:00pm
Total Posts: 918 | Joined: Aug 27, 2006 - 6:36pm



I'd imagine the weight of the water would draw the air Victor. As the speed increased, the water would have to fill the gap behind the steps if air couldn't get in. That would mean lifting a considerable weight not to mention the water having to make a sharp turn up. So the vent holes would supply the much easier flowing air to fill the gap. At speed, most of the air was probably supplied from the side of the steps as the hull lifted up and brought them out of the water.

Modern design, as seen in the link I posted, seems to embrace a deeper step with a curved forward surface and flatter bottom on them. I don't think they need air vents, the deeper step cuts come up high enough on the sides to supply the air. I used to race an R/C catamaran hydro hull that had a stepped bottom, the cuts behind the steps were deep and rose up past the chine quite a bit.

Hydrodynamic experts can stop sniggering now. I'm done propounding theories on subjects I know little about.




Posted By: Jeff D | Posted on: Jan 6, 2009 - 11:43pm
Total Posts: 1665 | Joined: Dec 21, 2006 - 1:30am



Hi Victor, both Dick and Jeff are close to the mark. The steps under the hull would have some form of connection to the louves on the side of the hull, this now explaines why the chine is so wide.This connection could be as simple as a section chiseled through the original chine.

So what makes it work .

When the boat starts to move forward the water is sucked out of the steps this creates a vacumn within the step which is filled by the air coming through the conection from the louver.With vents at the rear so they do not fill up with water(dosen't work to well like that).The air then exits the step under the hull (this will continue as long as the vacumn i.e. forward moition is maintained) on exiting the step the air and water meet creating a certian amount of turbulance.This turbulance breakes the boats surface tension by a certian amount this then allows the boat to move forward with less drag acting on its hull.

Thus accounting for the extra speed achived

This also explains why the boat was hard to control at slow speeds without enough turbulance being created the steps and louves would become just extra drag creaters on an other wise clean hull

Surface Tension."Those forces acting on a boats hull in water and equal in all directions."Thats why they put those massive great Packards in them , damm good engines too.

As i said Dick and Jeff were close, hope this helps you Victor .

Cheers from an Aussie, David.

D.buck

Posted By: David Buck | Posted on: Jan 7, 2009 - 4:15am
Total Posts: 332 | Joined: May 4, 2008 - 2:59am



I DON'T KNOW WHAT ITS WORTH, BUT INTRODUCING AIR INTO THESE STEPS SEEMS UNNECESSARY. THE HOLES IN THE SHEETMETAL SIDESTEPS SEEM TO BE FOR DRAINAGE. AT SPEED THE FREEBOARD DOESN'T CONTACT MUCH WATER. THE STEPS ON THE BOTTOM OF THE HULL WOULD BE EFFECTIVE THROUGH SIMPLE CAVITATION. THE AMOUNT OF AIR FLOW NEEDED WOULD BE TREMENDOUS. SINCE THIS WAS EXPERIMENTAL, I DON'T THINK THAT ELCO WOULD CUT LARGE HOLES INTO AN UNDELIVERED PT BOAT AND GET THEIR MONEYS WORTH. SLAP-ON STEPS MAKE MORE SENSE

Steve Tuhy

Posted By: Steve Tuhy | Posted on: Jan 7, 2009 - 8:52am
Total Posts: 114 | Joined: Oct 17, 2006 - 5:41am



Dick, I've been wrong so many times that almost any decision I come to about anything, I'll do the opposite.Except when fashion models are asking me to come to their place of course.

I still don't think that the 2nd image has the louver skins missing... The sun is low and forward in the 1st one casting deep shadows backwards. In the 2nd image the sun is high straight off the port making the shadows weak. And I'd think some structures would be visible if the skins were gone. The waterlines look like they're going over a curved surface too. Do you see that at all or is my past catching up to me?

One interesting bit is their height, almost snorkel-like. It would seem to point to low speed / high waterline use at least in part, maybe to help get on plane.

One of the profile plans I bought from the ptboats.org has the stepped hull, I'll try to dig it up and see if it can help explain anything.





Posted By: Jeff D | Posted on: Jan 7, 2009 - 12:31pm
Total Posts: 1665 | Joined: Dec 21, 2006 - 1:30am



This reply is a little off the subject but also a bit related. A former Chief Motor Mac once disagreed with me when I said that the boats would "plane" upon reaching a certain speed. He said that the boats did not plane. He gave me another word which I have completely forgotten. The boats certainly would level off upon reaching a certain speed and the rooster tail would flatten. Can any old hands give me a word for this leveling other than "plane"?

Posted By: QM | Posted on: Jan 7, 2009 - 1:35pm
Total Posts: | Joined: Unregistered



"On step?"



Posted By: Drew Cook | Posted on: Jan 7, 2009 - 2:19pm
Total Posts: 1227 | Joined: Oct 19, 2006 - 10:44am



QM;
ON STEP is the correct term.
TED



Posted By: TED WALTHER | Posted on: Jan 7, 2009 - 8:11pm
Total Posts: 2837 | Joined: Oct 16, 2006 - 7:42am




Jeff - - Can you see the EGG on my face . . .

You are correct; the lighting has made the louvers appear nearly invisible. I had read your earlier email about photo 2 but just couldn’t make out what you said you saw. This time I downloaded the photo and enlarged it in PhotoShop and applied some filters, changed levels settings, then with the burn tool darken up each area. Low and behold there they were “louvers”’, not brackets. I even outlined lightly the second to the last. To better define the object.

This angle shows the exhaust ports (the very dark spot) on the backside of the louvers – where either air, bubbles, spray, water or the combination of one or all are guided from the step planes and ported out of the louvers. From this photo the lovers are clearly fixed to the boat and not adjustable. They are clearly meant to vent but for what exact purpose I’m not really sure. Below is a partial doctored copy of photo 2. He best I can do with the resolution and size of the original then again lowered for posting for web viewing.

[image]http://i130.photobucket.com/albums/p249/ptboats/Victor%20Chun/LOUVERS-01.jpg[/image]





Posted By: Dick | Posted on: Jan 7, 2009 - 10:59pm
Total Posts: 918 | Joined: Aug 27, 2006 - 6:36pm



Cool Dick, nice Photoshopping!

I dug up the plan but it pretty much just lays out the steps. There is some historical information though:

[image]http://www.pt103.com/images/ptpics/BOSInboardProfileHullConstructionPlan496248RearSteps.jpg[/image]



Posted By: Jeff D | Posted on: Jan 8, 2009 - 4:49am
Total Posts: 1665 | Joined: Dec 21, 2006 - 1:30am



Hi David Buck,
I studied your reply of Jan. 7, 2009 in great detail. By George! I think I
got it. However, in your first sentence you wrote, as the boat moves
forward "the water is sucked out of the steps, thus creates a vacuum
within the steps." Do you mean " behind" the steps instead of "behind"
the steps. I assume the step is a solid piece of wood. Please advise.
Thanks for all your knowdedge.
Victor

Victor K Chun

Posted By: victorkchun | Posted on: Jan 9, 2009 - 3:04pm
Total Posts: | Joined: Unregistered



Jeff,

Please contact me offsite at PTConsultingNHR@aol.com. Thank you.

Garth



Posted By: TGConnelly | Posted on: Jan 9, 2009 - 4:32pm
Total Posts: | Joined: Unregistered



Hi Victor, in my reply to you i was following the line of thougth that you put foward in your post of Jan 7. "that the louves provided a layer of air under the boat". I should have explained that my thougths had a vent of some kind on the rear face of the step under the boat.

This vent could be either holes drilled into the face with a chanel leading to the chine and thence up to the louvers via the afore mentioned connection or, the rear face of the step may be hollowed out a small distance into the step and then a checkout would lead down to this hollow again from the chine connection.

Or nither theory is correct and the Elco steps as fitted were just solid pieces of timber and took advantage of the turblance they created to break the surface tension acting on the hull.

The reason i considered the chine cutout was the placement of the louvers which start a good 2/3 to 3/4 along the length of the steps and would allow the joining of the louver and the step with plenty of material to work with.

Another thing to think about is while there were a number of stepped hull designs around at the time not many of them carried the step up the sides as Elco did.

Steve Tuhy did bring up a good point and i agree with him if i owned a brand new boat i would not let anyone cut holes in it either, however we must remember that Elco had made 200+ boats at this time and they were always looking for ways to make them go faster and any hole in a timber boat could be repaired quickly if needed. This was proved when they had to remove the steps and louves and plug the screw/bolt holes that were left behind.

Just a point of interest there are a number of stepped hull designs that are currently in use today that use a system very close to the one i have described. Air is channeled down through the boat and exits at the rear of the step thus creating a layer of air under the boat for it to ride on. With the use of computers very fast boats are being built with differant forms of this system fitted.

Cheers David.

D.buck

Posted By: David Buck | Posted on: Jan 13, 2009 - 3:43am
Total Posts: 332 | Joined: May 4, 2008 - 2:59am