Hey there shipmates! I am touring the PT305 in New Orleans and came across a motorized rotating cutaway Packard 4M-2500 engine display. It is really interesting but raised a new question. Attached to the output shaft of the Joes Gears Transmission (F-N-R) was a new type of flexible coupling and some sort of gear unit (a reducer or something?) that I have never seen before. I asked a few of the guys at the museum and they did not know either. It looks like it has a 1:1 input /output speed and I cannot find any labels or nametags on it. I have seen an Elco Vee Drive before and it is not a Vee Drive. So my question is..... what is this thing and what does is its function? Hopefully somebody out there will know. I am asking for a friend....
Thanks Jerry
Transmission cutaway engine and Silver Flexible Coupling with gear unit at right
Cutaway gear unit
Jerry Gilmartin
PT658 Crewman
Portland OR
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Jerry I really don't know what that is , but it reminds me of a power take off on a tractor , could it help with transferring the power to the props? Regards
Scott Campbell 2nd gen,PT 248
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Interesting, but I do not think the coupling and gear box are PT boat related. As you know from PT 658, coming out of the transmission, PT boats were a direct drive. Other craft, such as ASRs, utilized Packard engines. As mention earlier it does look like a PTO for anther mechanism. Hard to tell, would need to research some more.
Bill Smallshaw
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Welcome to the Sunday morning world of the retired mechanical engineer! That should be taken as a warning.
Studying this picture and another one I found online of the same unit taken from a different angle, I believe this is a variation of an epicyclic gear set that provides an output speed higher than the input speed. I have no idea what its application would be, and as others have stated, it’s unlikely to be a PT boat application. Is there a maritime use where you’d want the propeller turning even faster than the Packard engine?
I made a drawing of how the gears interact, but the Upload Images button isn't appearing next to the box where I'm typing the reply. Without the drawing an explanation of how it works is rather difficult. The best I can do is to point out that the large gear on the right is fixed to the transmission housing - it does not rotate. The small gears in the center are attached to a shaft that runs through the center of the large gear on the right - this is the output shaft. The output shaft does not connect to the large gear on the right, it just passes through the center, and remember that the large gear on the right doesn't move at all. You can't actually see the output shaft passing through the large gear, but it has to be there for this unit to do anything at all. When the large gear on the left is turned by the input shaft from the engine, it turns the small gears in the center. There are at least three of the small gears and possibly four, and all are attached to the output shaft. When the small gears push against the stationary gear on the right, that makes the whole set of small gears and their output shaft turn in the same direction as the large gear on the left. Because of the smaller size of the gears in the center relative to the two gears on either side, the small gear assembly and output shaft turn faster than the input shaft. The actual speed ratio depends on the number of teeth on the large and small gears, but based on what can be seen I’d say it’s around a two to one speed increase.
I’ve never before seen an epicyclic gear set using bevel gears, but it makes sense in a high horsepower application like this. That’s because spur gears in a typical epicyclic gear set engage one gear tooth at a time and the input gear is much smaller than the other gears. These two factors make it prone to failure. This bevel gear arrangement provides an input gear that’s just as big and beefy as the rest of the gear set and the large gears on either side have four teeth engaged with the small gears at all times. Distributing high power through multiple gear teeth at the same time is the key to success. Keep in mind that the Joe’s gear box behind the Packard engine (if I understand it correctly) does not change the output speed relative to the input speed, it’s either in gear (forward or reverse) or in neutral. There are no spur gears increasing or decreasing the speed, and the spur gears used to create a reverse rotation aren't going to see full engine power. Some maritime application apparently needed shaft speed multiplication, and this was the answer that could handle around 2,000 horsepower. It just wasn't a PT boat. A more logical application might be an industrial engine driving a pump or generator that needs to turn faster than the engine, and that might be the original use of this unit. The Hall-Scott Defender V12 was used in such industrial applications, particularly large irrigation pumps, but I don’t think transmissions like this were used. Also, if you fed the power into the other end of this transmission, it would reduce the speed - it works in either direction.
Randy McConnell (Randall J. McConnell III)
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Jerry Gilmartin
TOP BOSS
Posted on: Mar 17, 2024 - 12:36pm
Thanks Randy!
This explanation helps a lot! I also think this was never installed on a PT boat. One bonus is that it is a moving exhibit, with a motor that spins around the entire works! I took a video of it in action and will try to both post it here and send you an email so you can watch how it moves. It is super interesting to see all the internal gears & etc. moving! One thing that was pointed out to me is that the output shaft speed appears to be exactly the same as the input speed. Confusing. But that is just looking with the naked eye and not using any sort of tach. The little motor can only spin the assembly around at 10-15 rpm so if there is a speed difference, it may not be as apparent at such low speeds. OK so give me some time and I will try to post that video asap.
Thanks all of you for your help!
Jerry Gilmartin
PT658 Crewman
Portland OR
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I look forward to seeing the video. That should verify my conclusion about which parts move and which stay stationary - or not! Calculating speed changes with epicyclic gears isn't as straight forward as with spur gears, so I might have it totally wrong. But if it doesn't change the speed of the output or reverse its direction, what's the point? It's not a power take off because a PTO has one input drive and two or more output drives. It takes power off a main drive and directs it somewhere else.
I love those motorizes displays. Maybe they tacked it onto the back end of a Packard just because it's fun to watch.
Randy McConnell (Randall J. McConnell III)
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This is a very interesting question. While I can see a M 2500 used for an industrial purpose, I would think tat is would not have been a very economic, nor practical choice.
That said, what else would want to benefit from the HP and at the same time increase the output RPM's. What else used Packards? How about hydroplanes. They certainly fit the needs, but I have never spent any time around one to examine the drive train.
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