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Elco 80' PT Boat Specifications

2010 September 14 update: Packard engine data added.

2010 March 1 update: Cleaned up a bit, added camber information, and fuel tank capacity corrected.

The following specifications were derived from Elco drawings, the Navy build manual, reference books, and the net. I've tried to be accurate but please let me know if you find an error or can supply more detailed information, thanks. Note that the Navy build manual is a later version of the 103 class manual and that there could be typos from the character recognition program used for converting the manual to the web.

For simplicity I use keel for both the keel and stempost. Technically the stempost ends at frame 9 and the keel begins. Depth measurements are from the plans horizontal baseline which is slightly below the lowest part of the planked hull. The baseline is parallel to the waterline. Measurements along the keel are given in both frame locations and stations. More about frames and stations can be found on the Hull component page.

Specifications, 1942 Elco 80' Patrol Torpedo (PT) Boat
Manufacturer Elco Naval Division of the Electric Boat Company, Bayonne, New Jersey
Length Per the Navy build manual:
Length overall, extreme: 80' 3" (963")

Per Elco drawings:
80' (960") to outside of planking from forward point to the aftermost point (with the transom angle, deck centerline would be an additional .5"). Rear guard at the transom extended out an additional 6".

942" to the end of the keel.

Beam 20' - 7" (247") beam over planking.

20' - 10 3/4" (250.75") extreme beam at outside of guard.

Max beam located at frame 24, 347" aft of the forward point, according to Elco Frame Offsets plan number 3005.

Length On Load Waterline (LWL) 73' 4" (880").

This is measured at the designed waterline, or where the water will be with the designed load on the boat.

It is located between station 0 (68") to station 10 (948"). Stations are 88" length divisions along the LWL and are used on the lines plan for cross-sectional lines. See the Hull page for details.

Amidships Halfway along the LWL, placing it 508" back from the forward point.
Depth, Molded 8' 9 1/2" (105.5") measured amidships.

This measurement can be confusing since it is measured from the bottom of the keel (minus the planking) to the deck sheer line.

Depth, Planked Keel Max planked keel depth is 5.25" above the baseline and located at frame 25, 359" aft of the forward point, according to Elco plan 3005, Frame Offsets.
Cambers / Crowns These are the curvature of surfaces. For example, using the deck sheer specs, when the beam of the hull is 21' the sheer (outer edge of deck) will be 4.5" lower than the deck centerline. With surfaces that have curved sides like the deck sheer this results in differing heights between the deck centerline and the deck sheer line as the beam changes.

Deck sheer: 4.5" in 21' according to Elco drawing 3086, Type Sections, and Deck Framing drawings. The sheer varied slightly to match the designed sheer line.

Chart house roof: 3.5" in 8' 3" according to Elco drawing 3231, Construction Of Bridge And Chart Room Trunk.

Day room roof: 3.5" in 8' 3" according to Elco drawing 3230, Construction Of Cabin Trunk.

Engine hatch: 2" in 8' according to Elco drawing 3086, Type Sections.

Deck hatch: 0.25" in 23.5" according to Elco drawing 3470 20" X 24" Hatch Frame And Cover. The crown runs fore to aft.

Finding the radius of a camber is useful for drawing the curve. The formula to derive a radius from the width and height of a camber is:
radius = (height/2) + ((width * width) / (8 * height))
Where height equals the camber and width equals the given "in" dimension. For those not having math as a second language, the order of the operations, indicated by the "( )", is important. Do the inner ones first like so:
1. Divide the height by 2.
2. Multiply the width by the width.
3. Multiply 8 by the height.
4. Divide the result from step 2 by the result from step 3.
5. Add the result from step 1 to the result from step 4 to get the radius.

Draft Elco PT Boat Waterline Measured from the draft clearance line at frame 69. This angled line is drawn from the center prop low point, to the point where it would angle up to touch the hull a bit aft of the bow. It ends up being about 20" below the baseline at frame 69.

Per the Navy build manual:

SECTION A-1, GENERAL, Principal dimensions. The following data are for information only:
Draft, normal, under 28" propellers: 5' 3/4"

Per other references, drawings and books:
5' - 3", 5' - 6" 1945

Weight 51 tons, 61 tons 1945 version
Speed 43 kts, 41 kts 1945 version
Engines Packard marine specs 1944 3 engines, supercharged Packard V12 model 4M-2500. Based on the Packard 3A-2500 aircraft engine.

Outboard engines were reversed with V drives, some later boats may have had outboard engines spaced farther apart facing the same way as the center engine.

From a Packard Engine 4M-2500 Manual, Specifications and Performance
Packard Engine 4M-2500 Specifications 1

Packard Engine 4M-2500 Specifications 2

Propellers PT Boat Elco 103 Class Propeller Profile Manufacturer: Federal Mogul Equi-Poise.

Center: 28" diameter x 28.5 pitch, right hand.

Outboard: 30" diameter x 30" pitch, right hand.

Pitch = inches traveled per revolution (with no slip), relates to the blades angle to hub.

Per Feb 2, 1943 BUSHIPS PT-103 Class Propeller drawing 78095:
Diameter: 28".
Pitch: 28".
Weight: 61 pounds.
Material: bronze casting to material specification Federalite-55.
Hub: 5.5" length, 3.5" front diameter, 3" rear diameter.
Text from drawing, note the drawing also spells Equi-Poise as Equipoise (in the patent notice) and that diameter and pitch are left blank:
  Propeller to be stamped as follows stamping to be on after end of hub and visible after nut is in place
  (A)-Federal Mogul serial number
  (B)-Federal Mogul symbol number
  (C)-Right Hand
  (F)-Federal Mogul and Equi-Poise trade marks
  (G)-Heat no.

About the information I've found regarding the government supplied propellers used on PT boats. Many information sources have them with 3 props 30" in diameter. I've also run across information stating that the center propeller was 28" with either a 28" or 28.5" pitch. They probably varied as horsepower increased, weight changed, and as each boat was tested. The center prop could of had a smaller diameter because it ran deeper and cavitated less. The propeller drawing that I bought from uses 28" as a diameter and pitch. It is dated February 2nd 1943 and marked "PT-103 CLASS".


Center: 28" diameter x 28.5 pitch, right hand
Outboard: 30" diameter x 30" pitch, right hand

Per the Navy build manual:

There shall be 3 aluminum-manganese-bronze right hand turning propellers per vessel. The diameter of the propellers shall not exceed 30 inches. Hub length will not exceed 8 1/2 inches.

SECTION A-1, GENERAL, Principal dimensions. The following data are for information only:
Draft, normal, under 28" propellers: 5' 3/4"

(a) Propeller test. This test shall be conducted in accordance with instructions issued by the Bureau of Ships for the type boat of each boatbuilder for the purpose of selecting the proper propeller for service conditions. Such a test shall be repeated as conditions of loading or design changes require.

Fuel Capacity PT Boat Elco 103 Class Dwg Bulkhead 47 3000 gallons of aviation gasoline in 3 tanks. The center tank holds 1300 gallons and the wing tanks 850 gallons each. The day room has a removable roof for tank access.
Range 259 miles at 35 knots.
Cruising Speed Maximum cruising at 2,000 rpm.

Slow cruising at 1,200 rpm.

Minimum cruising at 800 rpm.

Idle at 600 rpm.

Top Speed Max 3,000rpm, 40+ knots
Crew 11, 2 officers and 9 enlisted men, 1945: 17, 3 officers and 14 enlisted men.
Potable Water PT Boat Elco 103 Class Dwg Bulkhead 28 About 200 gallons. The chart house roof has a removable section, and the chart room a removable floor, for tank access.


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