The following notes cover the main features affecting personnel and material when operating a destroyer at full power. The conclusions and recommendations as to operation are based not only on the most interesting table, published with this article, of data and performance of the Paul Hamilton, under the command of Lieutenant Commander T. L. McCauley, and the Farragut, commanded by Lieutenant Commander John F. McClain, but also on the author's observation of full power trials of destroyers while serving as an engineer member of the Board of Inspection and Survey in 1919 and 1920 and while serving as squadron engineer of the eleventh destroyer squadron in 1923-24.
With reference to the table of full power data, note that the first two reported trials of the Paul Hamilton and the first reported trial of the Farragut were far from perfect trials, whereas the last two trials of the Paul Hamilton and the last trial of the Farragut were without penalty. These vessels also made perfect smoke prevention trials at the same time. The data taken on the reported trials of these two vessels (trials were consecutive) were chosen for publication because of the marked improvement made by them solely by standardizing operation on sound engineering principles as discussed in this article.
Taking the items in order as they appear in the table the discussion is as follows: [commanding officers of destroyers would do well to note particularly remarks under (a), (b), (c), (d), (e), (r), and (s).]
(a) Gallons Fuel on Hand at Beginning of Trial: The rules require that there be on hand at the beginning of the trial at least 45,000 gallons of fuel. Every effort should be made to reduce the fuel on hand when leaving an anchorage for the trial to 50,000 gallons. If trial is held enroute between ports, delay beginning trial, if practicable, until the oil on hand is about 47,000 gallons. It requires approximately 25,000 gallons of fuel to warm up to speed for one and one-half hours and conduct the two-hour full power and four-hour stroke prevention trials. A bonus trial requires about 10,000 gallons for one and one-half hours warming up and the one hour at ninety-five per cent of full speed.
The following method of stowing the fuel oil before a trial is recommended. It is believed that, without filling the forward peak tanks and with the after peak tank not over half full, the trim, with this stowage (50,000 gallons oil), will be within two inches of even keel. The stowage provides for an ample amount of oil in "D" and bridge tanks under a good head and stowed so as to practically eliminate the possibility of losing suction when rolling; a small reserve in the after-fireroom wing tanks; and the balance of the oil stowed as far forward as possible in order to improve trim.
Grand total bridge tanks, 17,681—of this 16,764 is available. (A-116 and 117 not to be used.) Cross connection sluices and deck drain to A-208 open, deck drains to 209 and 210 closed tight.
The total oil above is 36,468 gallons.
Place balance of oil on board (at time of getting underway) in A tanks, beginning with A-104, and working aft filling to ninety-five per cent capacity the tanks farthest forward. Note that with A-104, 105 and 106 ninety-five per cent full the total oil on board would be 50,169 gallons, which is just right to leave port.
(b) Displacement and Displacement Minus Fuel: All destroyers in this squadron were designed for a displacement of 1,215 tons with ship fully equipped, ready for sea, normal stores, ammunition and fuel (45,000). Due to alterations and stores on board above normal, the average displacement of the vessels of the squadron is 1,450 tons with 45,000 gallons fuel on board, or an increase of about 235 tons above the designed normal displacement. This increase in displacement has reduced the maximum possible speed about 2 knots.
The engineering rules attempt to eliminate the displacement handicap by basing the maximum allowed competitive speed on 30,000 s.h.p. and providing r.p.m. speed curves for each displacement in fifty-ton increments. If the information on which these r.p.m. speed curves for varying displacement were based had been correct, it would not make any difference at what displacement the trial were held. But practice has shown and recent special trials of the Brooks (representing Bath hull) and the Putnam (representing Bu C & R hull) (See Journal American Society of Naval Engineers, November, 1923) have corroborated the fact that the allowance for increased displacement as given by the engineering performance rules is not nearly sufficient. Therefore, to avoid handicap on displacement, which still, in reality, remains, although reduced, every effort should be made to run as light as possible.
(c) Trim.—Owing to the light draft of destroyers, it is necessary in order to obtain satisfactory tip immersion of the propellers, to incline the main shafting to the horizontal in a vertical plane. In destroyers built by the Bethlehem Ship Building Corporation, this angle is considerably greater than in vessels of the war program built by other companies and at navy yards. This inclination of the shafting to the horizontal decreases the efficiency of the propellers, (propulsive coefficient) and increases the s.h.p. per revolution. At full speed, a destroyer of the 1,215 ton class will squat about four feet. Whatever can be done to reduce this "down by the stern" condition will improve the chances of making the required r.p.m. With usual loading of destroyers in this squadron, it has been found possible to obtain a "dead in the water" trim between six inches down by the stern and six inches down by the bow, with only 45,000 gallons of fuel oil on board, forward peak tanks empty, after peak tank three-fourths full. Improvement in trim is practicable only by judicious stowage of fuel oil. Better trim can be obtained if care has been exercised in disposition of dry provisions and ammunition (the tendency is to stow the greater part of ammunition and dry provisions aft). According to the rules, the displacement for which the required r.p.m. are taken is the displacement before getting underway when the trial is made out from an anchorage; or, when the trial is held on runs between ports, it is calculated by subtracting oil expenditure from displacement just before getting underway. The taking of the draft should be supervised by an officer. Note that the draft figures for displacement are Arabic numerals on bow and Roman numerals on quarter. Both port and starboard readings should be taken to correct for list. The Arabic numerals aft give the draft of the lower tip of the propellers and are eighteen inches lower than corresponding Roman numerals on the quarters. If through neglect the draft marks have been obliterated, the draft may be obtained by taking the freeboard at the stern and at the bow (base of bull-nose) and calculating as follows (data from C & R General Information Book) :
With ship on even keel, loaded to 9' — 4" waterline, the freeboard is as follows:
At bow 17'— 1"
At stern 8' — 1"
The freeboard as measured should be subtracted from the freeboard 9' — 4" water line and the average of the resultant figures added to 9' — 4" to obtain mean draft.
Caution: Do not under read the draft. Note on the Paul Hamilton's June trial it is quite probable that the draft was under read enough to make 100 tons error in displacement.
(d) Days Out of Dock.—Fouling of bottom and propellers has a marked effect on ability to make required r.p.m. Whereas the controlling resistance on a destroyer at full speed is the wave making resistance, nevertheless fouling decreases the possible speed, thereby decreasing propulsive coefficient (increasing slip) and increasing s.h.p. per revolution. Fouling of propellers materially increases s.h.p. per r.p.m.
The interval between the dockings of destroyers is set by Bureau of Construction and Repair at not less than nine months and, if practicable to dock, not more than twelve months. The fouling is more rapid the higher the sea temperature, the less the cruising speed and the more the percentage of time spent at anchor. Fouling in certain harbors is very rapid, as at San Diego and in any tropical port. The rate of increase in fouling decreases with time out of dock.
When practicable, one of the two full power trials should be held within fifteen days after docking.
At intervals of not over three months the propellers should be cleaned by divers and examined for cracks and bent tips and every effort should be made to have this done at some time within two weeks before holding a full power or bonus trial.
Placing a seagoing vessel in fresh water for twenty-four hours will undoubtedly kill a great deal of the marine growth. This was successfully done during the summer of 1923 by sending the vessels of 31 and 33 divisions into Lake Washington (Seattle) for forty-eight hours; they were then eight months out of dock. Passing through the Panama Canal will clean the underwater body to a great extent.
(e) Gallons Fuel Burned Per Hour.—The data show that a perfect full power trial should be made burning between 4,000 and 4,800 gallons of oil per hour. Burning more than 5,000 gallons per hour would certainly overload the air supply available with the blowers at rated full speed (as indicated by heavy black smoke), the net result being a reduction in quantity of steam produced and overheating of boiler casing, uptakes and smoke pipes. The oil burned per hour should be kept in mind when choosing oil pressure, tip and plug sizes, and in disposition of oil prior to trial. If the Form "H" score for the trial is less than ninety-five per cent for DD's 296-335 or ninety per cent for DD's 251-295, you may surely look for one or more of the following: low vacuum, excessive steam consumption of auxiliaries, dirty boilers, low boiler steam pressure, or high water level or salinity in boilers.
(f) Steam Pressure at Boilers.—To make a 100 per cent full power trial, it is essential that the boiler pressure never drop below 265 pounds gauge, and in fact the pressure should be kept at 269 pounds. This requires careful setting of safety valves, and practice in oil control to eliminate fluctuations in boiler pressure. A falling off from the maximum allowed in boiler pressure increases steam consumption of main engines and blowers and makes operation of forced draft blowers at allowed maximum speed difficult without opening overload hand nozzles.
(g) Steam Pressure on Main Turbine—Steam Chest.—If the boiler dry pipes or steam line strainers are not fouled, the drop in pressure between boilers and main turbine steam chest should not be greater than five pounds for forward turbine and ten pounds for after turbine with main turbines at full speed. The main throttles must be wide open at all times during the trial. Speeding up or slowing of the turbines and maintaining of the steam pressure must be done, for G.E. turbine installation, by manipulation of the by-pass to the third stage; in the three turbine Fore River Curtis installation by manipulation of both HP turbine hand controlled nozzles and the by-pass valve from HP turbine first stage to the IP turbine steam chest, keeping HP steam chest pressure at maximum; and for Parsons Turbines by controlling with fifth stage by-pass. Keep the throttles wide open. Under no circumstances allow the main steam pressure at the forward engine room to drop below 250 pounds gauge.
(h) Steam Pressure on Third Stage of G.E. Turbines.—In order to make a perfect full power trial it is necessary to supply enough steam so that the pressure on third stage will not fall below 230 pounds gauge.
(i) Steam Pressure on First Stage HP Turbines and Steam Chest of IP Turbine in Fore River Curtis Installation.—The steam pressure on the first stage of HP turbine must be kept at 115 pounds continuously. This is done by manipulation of last hand controlled nozzle in use, together with the by-pass from HP turbine first stage to IP turbine.
In order to make a perfect trial the steam supply must be sufficient to maintain 250 pounds on HP turbine steam chest with all hand controlled nozzles open wide, and IP by-pass opened enough to keep first stage of HP turbine down to but at 115 pounds gauge.
(j) Vacuum on Main Condensers.—Trial data show that a vacuum of 27.1 inches at 100 per cent full speed is excellent on Bethlehem destroyers with injection of 60°-65°F. This was obtained with a thermometer in the exhaust trunk, and while subject to some error is still very much more reliable than readings with the six-inch gauges provided. With an injection of 80° an excellent vacuum would be 26.2 inches at 100 per cent full power. The above remarks apply only to Bethlehem built destroyers, which have no air ejectors and are consequently handicapped by the loss of at least one inch of vacuum at full power under what is possible with the Bath, Cramp, N. Y. Ship or navy yard main condensing plant, which is provided with an air ejector (augmenter).
No one point has more effect on ability to develop 100 per cent of required power than the vacuum in the main condenser. To obtain a good vacuum requires frequent tests for air leaks, constant vigilance in attendance on gland steam; full stroke, tight valves and good packing in air pumps, particularly the dry cylinder, and that the condenser tubes be cleaned on salt water side, particularly those tubes which supercool the air drawn out of the main condenser.
When the injection is higher than 70° F. the coolers on the air pumps should be used. The main air pumps should be operated with wide open throttles (full stroke) on full power trials and the cross connections between the two systems should be opened.
(k) Temperature of Injection, Overboard Discharge and Air Pump Discharge.—If the temperature of the injection is over 65°F. the overboard discharge valve should be wide open to permit full flow, if less than 65°, so adjust the overboard discharge valve (i.e., starting from full open and gradually closing it and noting temperature of exhaust trunk, air pump discharge and overboard discharge) that one has the highest air pump discharge temperature possible without suffering a dimunition in the vacuum on main condenser (increase in exhaust trunk temperature). One will find this procedure well worth while because of the increase made in the hot well temperature. This practice is, of course, permissible with an injection greater than 65°, but it is most probable that, with 65° plus injection, air leakage is so great that it will not be possible materially to choke off the circulating water without an immediate increase in exhaust trunk temperature. If the air pump discharge temperature is more than 5° below the temperature of the exhaust trunk and any choking off of circulating water increases the temperature of the exhaust trunk, one may be certain that the dry cylinder of the main air pump is overloaded. In this case, the only way to improve vacuum is to stop more of the existing air leaks.
As to the overboard discharge temperature, note this frequently enough to catch any high abnormal increases (if this occurs you have picked up kelp, a big pocket of air, or possibly the air vent on condenser heads may have become clogged) but make it the rule to regulate the overboard discharge valve having regard solely for increases in air pump discharge temperature without an increase in exhaust trunk temperature.
With an injection below 65°, one should be able to obtain an 85° air pump discharge without suffering a loss in vacuum below that possible with the Bethlehem main condensing plant at full power (twenty-seven inches in exhaust trunk). This would be a plant with very few air leaks.
(l) Temperature of Hot Well.—This varies primarily with the air pump discharge. It should be made as high as possible while obtaining best vacuum but not over 140° at full power. All steam line drains and the feed water heater drain should be led to the hot well. Further to increase the temperature, run auxiliary exhaust through the evaporator coils with coil drains wide open (blowing through) and water in shell of evaporator about two inches above bottom nut on shell gauge glass. With air pump discharge of 85°, it should be possible to obtain 115° in the hot well.
Always take suction on main feed pumps from the hot well, and not from C-101 (reserve feed tank). The auxiliary feed pump must be kept ready for instant use on a full power trial. Have these pumps on the direct suction (five inch line) to C-101. Have them turning over slowly (three double strokes per minute) and if sufficient make up feed is not obtained in this way speed up one of them. This is the proper way to make up feed on full power. C-101 should be heated to 120° before the full power trial.
(m) Temperature of Feed Leaving Heaters, Back Pressure and Feed Heater Drains.—Keep auxiliary exhaust pressure (back pressure) right up to fifteen pounds gauge. Note that the relief valves on the forced draft blowers turbine casings should be set to lift at twenty pounds gauge.
Drain the heaters to the hot well with drain valves wide open at heater and hot well. Heaters in Bethlehem destroyers are not equipped with proper and necessary means of bleeding off air, either from steam side or water side.
Bleeding the air from the steam side is essential to obtain maximum heater efficiency. Bleeding the air from the water side will improve the vacuum on the main condenser. To bleed the air from steam side, run a one inch connection from bottom of the gauge glass fitting on side of heater to the hot well, keeping valves on this line full open whenever heater is in use. To bleed the air from water side, braze a boss on the highest point of the feed discharge line leaving the heater and run a one-fourth inch line (or if larger line is used put a one-fourth inch orifice) to the line bleeding air from steam side. This installation is simple and will be of material benefit at all speeds.
It is noted from the data on enclosure that one may expect a 192° feed leaving heater with a fifteen pound back pressure and hot well at 110°. Many ships complain of the inadequacy of the feed heaters. They are very satisfactory if properly operated.
(n) Feed Heater, High Pressure and Low Pressure Drains.—These should be led to hot well. The feed heater drain should be opened wide open and no attempt made to keep a seal on the heater. All turbine drains should be kept closed except the drain from the exhaust end of the last turbine in series, which should never be closed.
(o) Generator Turbine Exhaust.—This should preferably be led to auxiliary exhaust line unless there is particular trouble with generator turbine shaft steam seal glands leaking badly when operating on back pressure, but when in good condition the glands will not leak. If the generator exhaust is led to main condenser direct there is sure to be an impairment in vacuum, such as to increase the steam consumption of the main turbines for given power much more than the decrease in steam consumption of the generator. If absolutely necessary to operate the generator condensing send its exhaust to auxiliary condenser.
(p) Pressure on Auxiliary Exhaust (Back Pressure).—Keep this at fifteen pounds gauge (the maximum allowed when operating turbine driven auxiliaries). See that all turbine driven auxiliaries have relief valves set at twenty pounds gauge.
(q) Fuel Oil Pressure, Temperature and Tip and Plug Size.—Very satisfactory atomization can be obtained at 200 pounds gauge at burners, there being practically no improvement with higher pressures. As the choice of atomizer tips and plugs is limited, it will be necessary to use a pressure higher than 200 pounds in order to burn the amount of oil required to make full power; therefore with tip and plug size chosen, adjust pressure accordingly, but the limit set by the rules is 300 pounds gauge at the boiler front.
As all burners are under the same air pressure and as adjustment of register vanes is impracticable it goes without saying that tip and plug size on all burners should be the same in order to burn oil at the same rate in each burner. If all the oil necessary to make 100 per cent trial can be burned without exceeding the 300 pounds limit with 3/32 tips (Bureau standard) and 1/16 x 3/32 plugs use this size. However, if this size will not burn a sufficient quantity of oil at 300 pounds pressure, the next higher combustion rate would be given by 7/64 tips with 1/16 x 3/32 plugs. Do not mix 7/64 and 3/32 tips even though some ships have done it and made perfect trials. Do not use 7/64" tips on two boilers and 3/32" tips on the other boilers, but keep the load on all boilers the same. The 1/16 x 1/16" plug is not recommended for any size tip. It will flood the 3/32" tip giving poor spray at any pressure and too wide a cone angle. The oil temperature should be such as to reduce the viscosity of the oil to 150 seconds Saybolt Universal (4° Engler). If the temperature to produce this viscosity is not known, and the Baumé gravity is eighteen or over it is safe to use a temperature 10° below flash point, provided the oil is not what is known as a blend. Blended oils are very irregular in viscosity and flash point characteristics. Another rough method of determining proper temperature of an oil for burning, which must be done before a trial, is to burn it first at flash temperature, air adjusted to give light haze, then reduce temperature of the oil 10° at a time noting when spray begins to get poor, then use temperature 10° above this point. If the oil is heated so as to reduce viscosity below 100 seconds Saybolt Universal (about 2½° Engler), there will be a marked reduction in capacity of the tips and panting'may occur if the heating has increased the oil temperature beyond the flash point.
One important point, especially in view of the meager oil data given destroyers by tankers or oil contractors, is to use on a trial only one delivery of oil. The chief engineer should foresee this at least one oiling in advance of a trial. It is well to state that oils received from different tanker cargoes should never be mixed, except possibly to produce a blend of a light oil with a heavy oil in order to lower the viscosity curve of a heavy oil. If this is done the mixing should be thoroughly done by pumping the oil from tank to tank several times. Too little attention has been given in advance of a trial to obtaining data on the proper temperature at which to burn the oil to be used on the trial.
(r) Air Pressure in Firerooms and Smoke.—The air pressure should be equalized between fire rooms at full power. This can usually be done by leaving the louvers open in the air lock doors. This would not endanger water tight integrity of ships nor be a source of danger in case of explosion in one fire room. Air pressure gauges should be used. Too frequently they are allowed to get in poor condition. The amount of air should be that sufficient to give a light haze smoke, but if sufficient steam to make a 100 per cent run cannot be generated with blowers running at allowed maximum speed do not burn more oil than will give a light brown. Any further darkening of the smoke means material reduction in efficiency of combustion (CO present) rapid fouling of fire side of boiler tubes, and, if smoke gets black, overheating of boiler casing uptakes and smoke pipes will result. The commanding officer can and should observe this carefully from the bridge.
Check the operation of the blowers on deck often, noting if each is pulling well. Frequently one blower will be allowed to slow and lose suction without detection by fire room personnel.
When making smoke prevention trial, if practicable, keep the apparent wind forward of the beam, and the umpire will be less likely to call penalties as any smoke made will dissipate more quickly. Usually an umpire considers smokeless operation that which does not have a smoke trail over 100 feet long.
(s) Sea and Wind, Conditions and Direction.—If practicable, work up for a trial with sea forward of beam and turn when ready to start trial so as to bring sea on quarter. No comment on wind is necessary except as noted in (r) above, when running smoke prevention trial. Steering should be done by the chief quartermaster and, except in bad weather or to avoid danger, the helm used should not be over 2°, except on turn 5° and the ship should be allowed to swing about 5° either side of course.
(t) Although not required by the rules at least one preliminary trial of one-half hour at full speed and one-half hour smoke prevention are necessary in order both to train personnel (not excepting the commanding officer and engineer officer) and to test material, particularly blowers for speed, main engines for bearing trouble and main condensing plant for vacuum. Too often engineer officers consider because they have an excellent vacuum at low power that it will be good at full power. The vibration at full power is apt to open joints and loosen bolts that do not show up at moderate power and if this occurred on full power the trial would be a failure. A short preliminary trial allows one practically to eliminate the possibility of having these troubles.