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Old 01-12-2013, 03:40 PM   #1
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Packard V-12 Marine Engine

In another thread somewhere there was a short discussion of the engine used in the US PT boats of WWII. I was referencing some information today about this engine and thought I'd stick this up here for anyone who's interested.

The photo is from my copy of the operations and service manual for the Packard 4M-2500 marine engine.

While it is not an aircraft engine per se, its development has its foundation in an aviation engine, the famous Liberty V-12 of WWI. The Liberty was morphed by Packard into a series of engines for racing powerboats and hydroplanes during the 1920s and 30s. The engine used in the PT boats, the Packard 4M-2500, was a direct derivative of the latest of the racing boat engines.

But it's aviation heritage remained to a degree. It is an individual, wet-sleeve cylinder engine. When the cooling jackets welded around each cylinder would develop pinholes the PT motor macs would wrap a piece of rubber around the jacket and secure it tightly with big hose clamps.

The engine had a single magneto that fed power to two distributors. Each cylinder had two spark plugs, one powered by each distributor.

Horsepower was 1,200 @ 2,400 rpm. In an emergency the engine could be run at 2,500 rpm.

Here is a footnote from the manual that might be of interest to the folks who like to debate power, prop size, etc. This was Packard's take on it at the time:

"Horsepower at any engine speed is a function of propeller size and boat load and is indicated by manifold pressure. Propellers should be selected to permit the engine to turn up to 2,500 rpm with the manifold pressures shown in the above table when the boat is properly trimmed and carrying maximum service load including full fuel tanks."

Full fuel in this case was 3,000 gallons.

Engine power was set using manifold pressure and the manual has charts for the various combinations of manifold pressure and rpm.

The three, three-bladed propellers all turned the same way with left-hand pitch.
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Old 01-12-2013, 03:52 PM   #2
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If I ever get those hydrofoils ip and running I'll need this baby for a good turn of speed. Perhaps I should rake my windows aft as well.

Was it mostly aluminum?

I'll bet it required very high octane fuel w the blower.

Blip the throttle w all three in gear and turn 90 degrees?

Thanks Marin
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Old 01-12-2013, 04:07 PM   #3
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No, the engine was not aluminum. I don't think any engines were back then but I could be wrong. It weighed 2,950 pounds dry. It could run on 87 octane fuel if necessary but the recommended fuel was 100 octane aviation fuel.

The PTs were almost unmaneuverable at idling speed. The Elco was worse than the Higgins in this respect. The Elco had three tiny spade rudders about the size of the ones on our GB if not smaller, one behind each prop. At speed they were great but at slow or idle speed they were virtually worthless. Maneuvering at slow speed was done with the two wing engines.

The Higgins was a bit better but not much. It had two much larger spade rudders, one behind each of the outboard props. I've been on a restored Higgins boat powered with the original Packard engines (the only one in the world today). We were out on the Willamette River and the thing was an absolute bitch to maneuver back into its slip. People on the dock pushing with poles was more effective that the engines, props, and rudders were.

And the guy driving was an ex-PT skipper from WWII with a bazillion hours driving a Higgins boat. He told me afterwards that they were all this way. You just got them up to the dock or the raft as best you could. The good news was there were always lots of people around to lend a hand.

A favored technique in the combat theatres, particularly if it was windy, was to bring the boat in fast almost up to the dock or raft, then pull the engines to idle, the motor mac in the engine room would shift all three to reverse, and then the skipper would give a huge blast of power to stop the boat next to the dock or raft. The theory was the boat would always be moving fast enough to give the rudders some authority. Most of the time it worked great. A few times it didn't.
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Old 01-12-2013, 06:42 PM   #4
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Interesting concept... but the additional 11 redundant cylinders is a bit much?
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Old 01-12-2013, 07:00 PM   #5
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Whadua think'in SS? A one cylinder 1200hp engine?
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Old 01-12-2013, 08:41 PM   #6
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Eric--- A follow-on correction to my answer to your earlier question. I was looking up more detail in my Packard 4M-2500 operator's manual to use in my work today and found this: (the bold emphasis is mine).

--------------------------

b. Basically the engine consists of two banks of six individual closed-end type steel cylinders, with welded-on water jackets, mounted at an inclined angle of 60 degrees on a cast aluminum crankcase. The crankshaft is forged alloy steel, counterweighted, and carried in eight shimless, removable type, shell bearings. A harmonic vibration damper is fitted to the supercharged end of the crankshaft.

c. Fork and blade connecting rods and forged aluminum pistons are used. The two exhaust and two intake valves per cylinder are actuated by a single camshaft on each cylinder bank through end-fulcrum-type rocker levers. A gear driven vane type fuel pump supplies gasoline to the downdraft, floatless, aviation-type carburetor located on the inlet side of the gear-driven centrifugal supercharger.

-------------------

So my statement that the entire engine was made of iron/steel is incorrect.
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Old 01-13-2013, 11:02 AM   #7
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Beautiful engine... just being facetious about the 11 redundant cylinders.
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