Editing PT boat (section)

===Plywood Derby===
====Background====
In March 1941, during a heavy weather run from [[Key West]] to New York by Motor Torpedo Boat Squadron 2 (MTBRON&nbsp;2), Elco 70-footers pounded heavily in {{convert|8|to|10|ft|m|adj=on}} waves even at moderate speeds, and seas continuously broke high over the bows. Operating personnel reported extreme discomfort and fatigue. All boats suffered from some sort of structural failure: forward chine guards ripped away, bottom framing under bows broken, side planking cracked [indicating lack of longitudinal strength], and other weaknesses were reported. In April MTBRON&nbsp;1 reported enthusiasm over the 81-foot Higgins (''PT-6''), and with the ''PT-6'' showing such good seakeeping, further purchase of Scott-Paine boats was unnecessary. In early 1941 the [[U.S. Navy Bureau of Ships]] lent Packard engines to both Huckins and Higgins, which wanted to build competitive boats at their own expense.

A Chief of Naval Operations PT Boat Conference convened in May 1941 to discuss future PT characteristics. All PTs prior to the {{convert|77|ft|abbr=on}} Elcos had been found defective, and it was probable the extended {{convert|70|ft|abbr=on}} Elco would not be an improvement. The conference recommended a series of comparative tests to evaluate what turned out to be five new designs of motor torpedo boats. The conference strongly recommended that no more Elco 77-footers be ordered until the tests had shown that they were indeed satisfactory.<ref>The Chief of Naval Operations,''Report of Conference on Motor Torpedo Boats'', Op-23D-KM, PT/S1(410414)Serial 181923 (Navy Department, 17 June 1941)</ref>

====Board of Inspection and Survey====
The [[Board of Inspection and Survey]], headed by Rear Admiral [[John W. Wilcox Jr.]], conducted comparative service tests<ref name=board>Board of Inspection and Survey, ''Report of Comparative Services Tests of Motor Torpedo Boats Held July 21–24, 1941 and August 11–12, 1941 at New London, Connecticut'' (Navy Department, August 14, 1941)</ref> off [[New London, Connecticut]], from 21 to 24 July 1941, using the following boats:

* ''PT-6'': {{convert|81|ft|m|adj=on|abbr=on}} Higgins; 3 Packard {{convert|1200|hp|abbr=on}} engines.
* ''PT-8'': {{convert|81|ft|m|adj=on|abbr=on}} Philadelphia Navy Yard; aluminum hull; 2 [[Allison Engine Company|Allison]] {{convert|2000|hp|abbr=on}} engines, 1 [[Hall-Scott]] {{convert|550|hp|abbr=on}} engine.
* ''PT-20'': {{convert|77|ft|m|adj=on|abbr=on}} Elco; 3 Packard {{convert|1200|hp|abbr=on}} engines; equipped with special propellers; special strengthening added to hull framing and deck.
* ''PT-26'', ''-30'', ''-31'', ''-33'': Same as ''PT-20'', except with standard propellers and without special strengthening.
* ''PT-69'': {{convert|72|ft|m|adj=on|abbr=on}} Huckins; 4 Packard {{convert|1200|hp|abbr=on}} engines.
* ''PT-70'': {{convert|76|ft|m|adj=on|abbr=on}} Higgins; 3 Packard {{convert|1200|hp|abbr=on}} engines.
* One {{convert|70|ft|m|adj=on|abbr=on}} MRB-8 (Motor Rescue Boat), built for the [[Royal Navy]] by Higgins; 3 Hall-Scott {{convert|900|hp|abbr=on}} engines.

Each member of the board conducted an independent inspection of every boat class, evaluating them for structural sufficiency, habitability, access, arrangement for attack control, and communication facilities.<ref name=board /> Boats were also evaluated under two conditions of armament loading: loaded and fully equipped with four {{convert|21|in|cm|abbr=on}} torpedoes and sufficient fuel to operate 500 NM at 20 knots; and fully loaded with two {{convert|21|in|cm|abbr=on}} torpedoes and ten {{convert|300|lb|abbr=on}} depth charges with sufficient fuel to operate {{convert|500|nmi|km smi|abbr=on}} at {{convert|20|kn|km/h mph|abbr=on}}.<ref name="board" /> Boats would have their tactical parameters of each design determined by photographs from an airship.<ref name="board" />

=====First open-ocean trial=====
Lastly, there was a demonstration of seakeeping qualities and hull strength by making a run at maximum sustained speed in the open ocean. An accelerometer was installed in the [[pilot house]] of each boat to record "pounding". Conducted on 24 July 1941, this open-water trial, {{convert|190|nmi|km smi|abbr=on}} at full throttle, was referred to by PT personnel as the "Plywood Derby". The course started from the mouth of New London Harbor, to Sarah Ledge, then led around the eastern end of [[Block Island]], then around Fire Island Lightship, finishing at [[Montauk, New York|Montauk Point]] Whistling Buoy.<ref name=board />

At the time, only the Elco 77-footers were loaded with armament. The other competitors had copper ingots added topside (mostly in the turrets) to make up the difference. This resulted in severe conditions for several of the boats during the trial and accounted for the transverse failure in ''PT-70''{{'}}s deck and subsequent hull failure as the copper fell into the hull.<ref name=board /> Nine boats participated in the trial.<ref group="note">''PT-26'' had previously developed deck failures while conducting standardization trials off Block Island on 21 July 1941.</ref> Six boats completed the trial, while three withdrew: ''PT-33'' suffered structural damage off Block Island; ''PT-70'' was damaged by loose copper ingots; and ''MRB'' developed engine trouble at the start of the run.<ref name="board" />

By class, ''PT-20'', an Elco 77-footer, came in first with an average speed of {{convert|39.72|kn|km/h mph|abbr=on}}; followed by ''PT-31'', with an average speed of {{convert|37.01|kn|km/h mph|abbr=on}}; ''PT-69'', the Huckins {{convert|72|ft|m|adj=on}} boat, was third with an average speed of {{convert|33.83|kn|km/h mph|abbr=on}};<ref group=note>The Huckins boat experienced a high pressure oil failure and had to go "Dead in the Water" in order to effect the repair.</ref> ''PT-6'', the Higgins 81-footer, with an average speed of {{convert|31.4|kn|km/h mph|abbr=on}} was fifth; and ''PT-8'', the Philadelphia Navy Yard boat, was last, at {{convert|30.75|kn|km/h mph|abbr=on}}. The other two Elco boats, ''PT-30'' and ''PT 23'' (standby boat), followed ''PT-31'', placing before ''PT-69''.

[[File:PT-31 crossing the "Plywood Derby" finish line at Montauk Point, Long Island, 24 July 1941.jpg|thumb|Second place PT-31 crossing the finish line during the "Plywood Derby".]]

The accelerometers ranked the boats as follows: first was the Philadelphia Navy Yard ''PT-8'' with the least pounding, second was the Huckins ''PT-69'', third was the Higgins ''PT-6'', and last were the Elco 77-footers.<ref name=board />

=====Second open-ocean trial=====
Because of the problem with ingot loading, a {{convert|185|nmi|km smi|abbr=on}} trial with the PTs fully fitted out was conducted on 12 August 1941. Four boats—''PT-8'', ''PT-69'', ''PT-70'', and MRB—returned and Elco sent two new boats, ''PT-21'' and ''PT-29''. During this trial, boats faced heavier seas, as high as {{convert|16|ft|abbr=on}}. All except the Huckins (''PT-69'') completed the run. The Huckins withdrew because of a bilge stringer failure. The Higgins 76-footer (''PT-70'') completed the entire run but also suffered structural failures: attachments between planking and web frames pulled loose and deck fastenings near engine hatches showed extensive failures. ''PT-21'' suffered minor cracks in the deck in the same location, but not to the same extent, as previously observed in ''PT-26'', ''PT-30'', and ''PT-33''. ''PT-29'' was assigned as a pace boat with ''PT-8'' in order to generate a pounding comparison.<ref name=board />

The average speed results from the {{convert|185|nmi|km smi|abbr=on}} course were: Elco 77-footer (''PT-21''), {{convert|27.5|kn|km/h mph|abbr=on}}; Higgins 76-footer (''PT-70''), {{convert|27.2|kn|km/h mph|abbr=on}}; Higgins MRB and Philadelphia Navy Yard boat (''PT-8''), {{convert|24.8|kn|km/h mph|abbr=on}}. Accelerometers were again installed in the pilot house of each boat, but the readings were incomplete because the violent motion of the boats made observations difficult and in some cases necessitated abandonment of the observing stations. Further, many of those taken were beyond the normal range of the instruments and were considered inaccurate. Elco boats were found to pound heavily and confirmed previous reports of crew discomfort.<ref name=board />

====Findings====
The Elco 77-Footer Design Demonstrates:<ref name=board />
# Ability to make a maximum sustained speed of 39.7 knots; maximum speed 44.1 knots with heavy ordnance load.
# Maneuverability satisfactory except for a large turning circle of {{convert|432|yd}}.
# Space available for four 21" torpedo tubes.
# Structural weaknesses resulting in transverse fractures of deck planking.
# Tendency to pound heavily in a seaway.
# Fittings and finish unnecessarily refined.
# Cost to the Government fully equipped $302,100.

The Huckins 72-Foot Design Demonstrates:<ref name=board />
# Ability to make a maximum sustained speed of 33.8 knots; maximum speed 43.8 knots with light ordnance load.
# Maneuverability satisfactory with a turning circle of {{convert|336|yd}}.
# Space available for two 21" torpedo tubes and ten {{convert|300|lb|kg|adj=on}} depth charges.
# Structural weaknesses resulting in fracture of bilge stringers.
# Very little tendency to pound in a seaway.
# Fittings and finish appropriate for a motor torpedo boat.
# Cost to the Government fully equipped $263,500.

The Navy Yard Philadelphia 81-Foot Design Demonstrates:<ref name=board />
# Ability to make a maximum sustained speed of 30.7 knots; maximum speed 33.9 knots with light ordnance load.
# Maneuverability unsatisfactory due to inability to reverse outboard engines with a large turning circle of {{convert|443|yd}}
# Space available for two 21" torpedo tubes and ten {{convert|300|lb|kg|adj=on}} depth charges.
# Structural strength is adequate.
# Tendency to pound severely in a seaway.
# Fittings (Navy standard for combatant ships) entirely too heavy and cumbersome for this type of craft. Finish adequate.
# Cost to the Government fully equipped $756,400.

The Higgins 81-Foot Design Demonstrates:<ref name=board />
# Ability to make a maximum sustained speed of 31.4 knots; maximum speed 34.3 knots with heavy ordnance load.
# Maneuverability satisfactory with a turning circle of 368 yards.
# Space available for four 21" torpedo tubes.
# Structural strength adequate.
# Moderate tendency to pound in a seaway.
# Fittings and finish satisfactory.
# Cost to the Government fully equipped $206,600.

The Higgins 76-Foot Design Demonstrates:<ref name=board />
# Maximum sustained speed of 27.2 knots in rough seas; maximum speed 40.9 knots.
# Maneuverability satisfactory, turning circle not determined photographically, estimated 300 yards.
# Space available for four 21" torpedo tubes.
# Structural weaknesses caused failures in transverse bottom framing, separation of side planking from framing and extensive failures of deck fastenings.
# Moderate tendency to pound in a seaway.
# Fittings and finish satisfactory.
# Cost to the Government fully equipped $265,500.

The board arrived at the following recommendations:<ref name=board />
# That the Packard power plant having been found highly satisfactory be adopted as standard for future construction.
# That the ordnance installation of future motor torpedo boats consist of two torpedo tubes, machine guns and depth charges.
# That the Huckins 78-foot (''PT-69'') design be considered acceptable for immediate construction.
# That the Higgins 80-foot (''PT-6'') design suitably reduced in size to carry such ordnance loads as are required by our Navy be considered acceptable for immediate construction.
# That the Elco 77-foot design be considered acceptable for future construction provided changes in the lines are made to reduce the tendency to pound in a seaway, and the structure be strengthened in a manner acceptable to the Bureau of Ships.
# That the Philadelphia 81-foot boat (''PT-8''') be stripped of excess weight and be re-engined with three Packard engines.

The board also had the following opinion on structural sufficiency: "During the first series of tests (21–24 July) the Huckins design (PT-69), the Philadelphia design (PT-8) and the Higgins design (PT-6) completed the open sea endurance run without structural damage. The Higgins 70' (British) boat did not complete this run because of engine trouble. The Higgins 76' (PT-70) and boats of the Elco 77' (PT-20 Class) developed structural failures even under moderate weather conditions prevailing. In the interval between the first and second test periods the PT-70 was repaired and an effort made to eliminate the causes of the structural failures. However, during the second endurance run, which was made in a very rough sea for this size boat, structural failures again occurred in PT-70. PT-69 and PT-21 experienced structural failures during the second run though these were much more localized as compared with those found on PT-70. The Board is of the opinion that certain changes in design are required to enable PT-69 and boats of the PT-20 Class to carry safely their military loads in rough weather."<ref name=board />

The board results provided very important benchmarks in the infancy of PT boat development.{{citation needed|date=June 2020}} This type of craft presented design challenges that were still issues decades after, but there are some significant conclusions from the above recommendations and their order of merit. Those are:<ref name=board />

# The Packard were the engines of choice.
# The Huckins 72-foot (''PT-69'') and a reduced Higgins 81-foot (''PT-6'') design were to be placed into production. Following an October 1941 BuShips conference and its new set of navy design requirements which included room to support four {{convert|21|in|cm|abbr=on}} torpedoes and an upper length restriction of 82', the next two orders for pre-war PT boats (''PT-71'' through ''PT-102'') were awarded to Higgins and Huckins.
# Even though the Elco 77-footers posted the fastest speeds, all seven Elcos suffered from structural damage and severe pounding causing the Board to recommend a redesign to correct these deficiencies. Elco competed for the ''PT-71'' to ''PT-102'' contract but did not win due to their higher unit price. After the start of the war and significantly revising their unit cost, Elco received the next PT boat order after Higgins and Huckins. This was to be their new Elco 80-foot design.

[[File:ELCO and Higgins PT boats, Know Your PT Boat US Navy July 1945.jpg|thumb|upright|Elco and Higgins PT boats, as published in a 1945 training manual]]