PT 1 thru PT 4 based on the 25ft aluminum test model 9. Model was requested for use during training.
Original 3M2500s were left (port engine) and right (starboard engine). These were upgraded to two right 4M2500s in Jan 41. The engine and fuel tank compartment metal framing is all aluminum.
Construction: Considered superior and boat was 10% lighter than contract (light load 38,000 lbs – trial displacement 56,600 lbs). In comparison, sister boats PT-1 and PT-2 built in Miami were about 4,000-6,000 lbs heavier (not sure if this was due to construction or equipment). Items such as the portholes were light weight aluminum and the boat even used a lightweight Northill Anchor (same typed used by seaplanes).
Performance: Boat handled 8-10 ft waves very well and was compared favorably over PT-9’s pounding. Boat turned easily on a very close radius and gave a feeling of complete stability in turn (banked very well into turn). At 2000 rpm, boat turned in 4 1/2 boat lengths. Maintained a pretty constant 4 degree trim angle. Hump speed approximately 12-16 knots.
Big problem seemed to be the prop slip, which reduced the HP. At a top speed of 34 knots (2400 rpm with 3M2500s), boat was losing an estimated 450 HP. Two different sets of props were tested (first 25 x 23 and then 26 x 27) a third was requested (greater pitch and increased blade area) for model testing with the tests completed 5 months after the transfer of the boat to Lend-Lease. Hull performance graphs indicate the boat hull design would easily allow speeds up through 40 knots, however I could not find any follow on performance tests with the 4M2500s or if a third set of different size props were ever installed. Looking at all the early PT boat BuShips data, props, either having the wrong size (P and D), using race type wheels which wore out quickly, or suffering from excessive cavitation, seem to be a constant theme.
As far as critiques from the various reports, maneuvering and seakeeping were excellent, as were the cockpit layout and internal arrangement, however the boat’s small size (59 ft), restricted deck size due to the rolled chine and deck mounted mufflers, and the stern launched torpedoes came up on the negative. In response to the restricted deck, it was stated that the rolled chine gave this light weight boat great strength (it is true she never suffered the hull and deck problems of boats without the rolled chine). Since she planed early, not sure how well her design would have taken to weapons overloading and her small fuel capacity (1665 gal) would have also been a limiting factor. Lastly, having to run on 1 prop required excessive rudder to drive her at what turned out to be an inefficient speed (just below hump speed). Her best operational speed seems to have been about 25-26 knots.
Of note, PT-4 was built with two 3M2500s and was suppose to receive a centerline 700 HP Allison. Found no indication that this Allison engine was ever installed (initial trials done with just the two Packards).
PT-3
Considering that the US Navy really had no idea what they wanted at the time of her contract, she did directly address the severe weight (transportation) requirements and incorporated many advanced features.
Some noteworthy design features.
– oak steam bent framing spaced every 10 and continues through barrel back.
– curved tumble home provides strength and stiffens hull, and eliminates normally weak deck edge to hull transition.
– double longitudinal planking provides lightweight strength and eliminates additional weight requirement of sandwiched cloth/canvas.
– use of carriage bolts to secure planking to lightweight framing, allows crew to tighten hull from inside.
– combination of framing structure with planking provided a very strong and mildly flexible hull.
– hull form is a warped plane design and overall narrow in design, but keeping the stern wide, in comparison to midships, seems to have minimized suction and stern squatting. Photos indicate that boat lifted up on step at a constant angle. As fuel consumed, weight would shift slightly forward.
– used two Packards for power (first PT Boat with these) For this design, the Navy required the engines to be mounted on a steel frame. In order to accommodate the engines, boat uses some sort of “v” drive. PT-3’s engine compartment construction has a forward and aft steel bulkhead with engine hoist. Hull and deck framing are wood. During the construction in 1939, both PT-3 and 4 were delayed by four months due to the unavailability of the new 3M2500 Packards.
– muffler system (although huge)
You can understand why this small boat was considered obsolete once the Navy figured out what they didn’t want (stern fired torpedoes), but I believe she was an important design worthy of note in PT Boat development and exceeded the designs of newer boats in frame and hull construction and showed the experience of George Crouch.
The hull is relatively straight chine aft of midships (widest part and transom only differ by 2 ft) and the back portion of the hull only has a slight change in deadrise. The hull is also not concave in form, you would expect suction loads to be on the lesser side and would not expect to see much squatting of the boat on plane. Trim angle on plane (from photographs) estimated at about 2.5-3°.
Because of the position of the fuel tanks (aft) and the weight of the engine room steel framing and engines, the center of gravity (CG) for PT-3 is pretty far aft. The center of buoyancy (CB) is guestimated at about 23-21 feet from the transom. As she starts to plane, CB would move aft and probably move very close to the boat’s CG which I believe to be about 20-18 feet from the transom.
She probably rides very well on glass calm based on other George Crouch designs. Deadrise is good at entry indicating potential for a smooth ride, however, in rougher sea states, her lack of a deep forefoot would probably result in some pounding forces, although the steep deadrise and slight convex shape of the bow would help. Having such a large hull sail area out of the water forward would probably make PT-3 very susceptible to beam wind forces when on plane. When operating at lower speeds, the CG being aft of the CB would probably make PT-3 susceptible to yawing motions in following seas. As for turning, she was probably good at slower speeds, but would suffer a bit at higher speeds due to not having the forefoot in contact with the water.
PT-3s actual hump speed is probably somewhere about 25-26 kts. Even with the steel framing in the engine room, weight saving building techniques are obvious, so she was intended to be a planing hull design.
- Laid down by the British Power Boat Co., Ltd., Hythe, Hampshire, England
- Acquired by the Navy 24 July 1940, placed in service and assigned to Motor Torpedo Boat Squadron ONE (MTBRon 1) for evaluations
- MTBRon 1, under the command of Lt. Earl S. Caldwell, USN, was the first squadron commissioned, and originally was made up of experimental boats
- Transferred 8 November 1940 to Motor Torpedo Boat Squadron TWO (MTBRon 2) under the command of now Lt. Comdr. Caldwell
- MTBRon 2 tested the first 70′ Elco boats in Florida and Caribbean waters in the winter of 1940/41
- Transferred to the Royal Navy 11 April 1941 and reclassified HM MTB-258
- Transfer to the Royal Navy canceled, subsequently transferred to Canada 23 September 1942 and reclassified V-264 where she served in the Halifax and Gaspe area as a harbor defense force vessel
- Reclassified S-09
- Reassigned in March 1943 to Quebec for blackout patrols on the Saint Lawrence River
- Reassigned in 1944 to Toronto, Ontario as a range control and safety vessel
- Returned to U.S. custody 1 February 1945
- Sold for scrap 5 September 1946Naval Vessel Register of 1 January 1949 lists transfer to the War Shipping Administration in October 1946.Specifications:
- Displacement 55 t.
- Length 70′
- Beam 20′
- Draft 5′
- Speed 41 kts.
- Armament: Four 18″ torpedoes and two twin .30 cal. Browning machine guns Torpedoes removed prior to transfer. Machine guns retained and eight depth charges added by Royal Canadian Navy
- Propulsion: Three 1,500shp Packard V12 M2500 gasoline engines, three shafts Reengined with two 550hp Kermath V-12 gasoline engines.
