Engineering Training



Assignment Sheet Number 62B-416



Small boats are used throughout the Navy for a multitude of purposes, from liberty launches and man overboard recoveries to official transports (admiral's barges and captain's gigs). A naval officer should have some knowledge of small boats, since he or she officer may be assigned duty as a boat officer. The purpose of this lesson is to increase familiarity with the operation and maintenance small boat engines.



Terminal Objective:

11.0 DESCRIBE and EXPLAIN the function, theory of operation, location, operating parameters, design characteristics and maintenance requirements of shipboard auxiliary systems and support equipment.(JTI:A)


Enabling Objective:

11.117 DESCRIBE the construction, function, operation and maintenance of the following ship's boat engines and components:

a. GM 6-71 diesel engine

b. Westerbeke diesel engine

c. Fresh water system

d. Air intake and exhaust system

e. Lube oil system

f. Transmission

g. Fuel oil system

h. Electrical system

11.118 UNASSIGNED; reserved for future use.

11.119 UNASSIGNED; reserved for future use.

11.120 UNASSIGNED; reserved for future use.



  1. Read Information Sheet 62B-416.
  2. Outline Information Sheet 62B-416 using the enabling objectives for lesson 62B-416 as a guide.
  3. Answer study scenario questions.


As the Auxiliaries Officer, you have been tasked to give a lesson plan to the engineers and deck personnel who are qualifying to operate and maintain the ship’s boats. Since your ship has more than one type of boat, the lesson plan must cover information common to all boat types.

  1. Describe the common features and systems of all boat types


  3. How is fuel quality monitored for ship’s boats and how does fuel quality affect engine operation?


  5. What are the special operating limitations for boat engines operating in freezing weather and what actions can be taken to assure that the boats remain in a ready status?


  7. What safety issues should be addressed in the lesson plan you are going to give?



Information Sheet Number 62B-416



Small boats are used throughout the Navy for a multitude of purposes, from liberty launches and man overboard recoveries to official transports (admiral's barges and captain's gigs). A naval officer should have some knowledge of small boats, since he or she may be assigned duty as a boat officer. The purpose of this lesson is to increase familiarity with the operation and maintenance of small boat engines.


(a) Engineman 3 and 2 NAVEDTRA 10541

(b) Marine Propulsion Unit Model 6087 NAVSEA Technical Manual 341-3479

(c) Boats & Small Craft NSTM chapter 583


  1. Types of diesel engines. Two of the more common small boat engines used in the Navy today are the 6-71 General Motors Detroit Diesel engine and the Westerbeke Model 4-107. The reason for their popularity is that they are reliable and parts are easy to obtain. General specifications are shown in the chart below.


GM 6-71 Diesel Engine

Westerbeke 4-107 Diesel





4.250 INCHES

3.125 INCHES



3.500 INCHES








225 HP @1900 RPM

25 HP @ 2400 RPM


  1. Systems. Both types of diesel engines share similar types of systems and they are discussed below in a general sense. For specific application the student is advised to consult the applicable technical manual.
    1. Fresh water system. The heat of combustion in a diesel engine can cause damage if it is not removed. The fresh water cooling system does this in much the same way a gasoline engine is cooled. Fresh water is circulated through the block, cylinder head, exhaust manifold jacket, and oil and transmission cooler by an attached centrifugal fresh water pump (figure 1). The heat rejected in combustion and developed by friction is absorbed by the fresh water coolant passing through a heat exchanger that has seawater flowing though it. The heat in the fresh water is rapidly transferred to the seawater in much the same way that heat from an automobile engine is removed by air flowing though the radiator.
    2. Seawater system. The seawater is supplied by a self priming positive displacement rotary pump. After the water is pumped through the heat exchanger to remove heat from the fresh water system, it is passed through the exhaust manifold to cool the exhaust before discharge overboard.
    3. Air intake and exhaust system. Air is provided to the normally aspirated engine through an air filter. Normally aspirated means that air is drawn into the engine by means of the engine’s own action. Other means of supplying air to an engine include turbo-chargers or blowers which force air into the engine. The exhaust system consists of a one-piece cast manifold and an exhaust goose neck elbow. Seawater that is directed overboard is admitted to the goose neck and then sent overboard.
    4. Lube oil system. The lube oil system consists of a positive displacement pump, piping and ports to feed main and big-end bearings, camshaft bearings, rocker shaft and timing drive (figure 2). The pump draws oil from the sump through a filter and sends it to the components to be cooled and then to a lube oil cooler that is cooled by fresh water.
    5. Transmission. In order to have both the diesel engine and the propeller of the boat operate at their ideal speeds, a speed reducing unit or transmission is used. The transmission is a self-contained unit with an oil system that is independent of the engine lube oil system. It consists of a pressurized oil system, a hydraulically actuated clutch for the forward drive and a hydraulically actuated reversing gear for astern operations. Cooling is provided by an oil cooler mounted on the engine that uses the fresh water system as a cooling medium
    6. Fuel oil system. The fuel system consists of those components needed to deliver fuel to the engine cylinders. The components are the fuel filters, fuel lift pump, fuel pump and injection nozzles. The fuel lift pump "lifts" the fuel from the tank to the fuel pump. From the fuel pump, it passes through a filter assembly and then injected into the cylinders at appropriate intervals.
    7. Electrical system. Small boats have a 24-volt electrical system and a generator to provide power to the engine components, miscellaneous electrical loads, and to recharge the battery so that the engine can be restarted. It is belt driven off the engine and has a voltage and current regulator. It is very similar to the electrical system in an automobile.

  2. Maintenance
    1. If possible, there should be one person assigned to each small boat. This provides consistency and ownership, hopefully improving material condition and readiness.
    2. The jacking bar turns the engine over by hand for maintenance to ensure the engine is not seized or binding in any way. Binding can happen if water is on top of a piston.
    3. The level in the fresh water expansion tank should be one inch below the top. Depending on the weather, the fresh water system should have a rust inhibitor or antifreeze. If the system is not treated, it could cause poor heat transfer due to corrosion build up and cause the engine to overheat or to develop a leak in the system.
    4. The cylinder block and the entire engine should be kept clean and preserved. Salt air will corrode the engine quickly. Cleanliness of engine internals will be easier, if it is kept clean. Once an engine has become badly corroded, it is very difficult to restore it to the proper material condition.
    5. Seawater system valves must be properly maintained or it could mean the sinking of a boat. All valves should be cycled weekly and the valve stems lightly coated with petroleum jelly or other lightweight grease. If the strainer is not kept clean, the engine may overheat due to insufficient water flow. Make sure the seawater pump is kept greased and that zinc anodes, if installed, are adequate.
    6. The air system silencer and screen must be kept clean. The engine will not operate properly unless it receives sufficient air for combustion.
    7. The lube oil system must always be kept clean and at the proper level on the dipstick. The lube oil filter and strainer are particularly crucial. Because the oil sump and transmission are located low in the boat, it is important to keep the bilge levels at a minimum. Verify oil levels with the dipstick and make sure that the fill and drain plugs are in place and tight. Due to the infrequency of use, the quality of the oil in a small boat engine must be closely monitored. The engine hours on the oil may be low but the condition of the oil might deteriorate if water is present in the oil. Periodic tests are done to determine lube oil quality.
    8. Always check for proper transmission fluid level on the dipstick. Small boat transmissions use lube oil type 9250 for a transmission fluid. Make sure all fittings are tight.
    9. Check to ensure that there are no leaks in the fuel oil piping system. Leaks could result in running out of fuel, could cause a fire hazard or could air bind the fuel oil system. Be sure fuel oil tanks are always full to minimize condensation, which is a major cause of fuel oil system failure. Water causes the nozzles and unit injectors to seize and the engine will not run. Use water indicating paste on the dipstick when checking the fuel oil level. Sediment and water shall be drained from the bottom of the tanks daily. Daily and before starting:
      1. Turn the primary scraper on the strainer 2.5 times and drain daily.
      2. Vent the system to remove air.
      3. Drain the secondary fuel oil filter until clean fuel oil shows.

    10. Check belt tension to ensure there is 1/2 inch to 3/4 inch deflection. More tension could cause the belt to break, bearings to wear faster and the shaft to warp. Less tension could cause slipping of the belt, which would cause the pumps and generator not to turn. This would cause the engine to overheat and batteries would not be recharged. Inspect for belt fraying and replace at the first sign of fraying.
    11. Proper care of the electrical system is essential to ensure that the diesel engine can be started and that lights are powered. The battery terminals and all electrical connections must be kept tight, clean and free of corrosion. Batteries must always be kept charged. Check the battery for specific gravity with a hydrometer (1.220 is normal and 1.275 is the norm for cold weather). The electrolyte level should be 3/8 inch above the plates. Add distilled water only.
      1. The generator maximum charge rate is 16-18 amps.
      2. An alternator is used on some newer installations.
      3. Current and voltage regulators protect the electrical system from overcharging.
      4. The system is equipped with fuses for the protection of the electrical system. All fuses are located in a fuse panel.

    12. Operation of the engine should be accomplished at least once a week in port and daily at sea. Do not run the engine at idle without a load for long periods of time. Never run an engine without cooling water. An engine should always be brought up to temperature before securing. Sometimes, this may require rigging a hose to provide sufficient cooling. Starting and stopping a diesel engine without allowing it to run eventually runs down the battery.

  3. Normal Operation
    1. Allow the engine to warm up before running at full speeds and to cool down before securing.
    2. Always ensure proper lube oil pressure and drive gear oil pressure before increasing speed from idle.
    3. Steering, throttle, and transmission cables must be kept well lubricated for continued smooth operation.
    4. Always keep the bilge level as dry as possible regardless whether the boat is in or out of the water.
    5. Before starting, make sure that the blower damper (emergency) is open. If you attempt to start diesel with the damper closed, the engine might suck in the blower oil seals causing significant damage.
    6. Always check the throttle control to ensure free movement of the injector control rack. If it is binding or stuck, it could cause the engine speed to run away.
    7. After an engine is started, be sure all pressures are normal and check the engine for any leaks or abnormal sounds. Make sure there is seawater flow overboard. Check the ammeter to ensure the electrical system is working properly. Check fresh water temperature to ensure all systems are aligned properly.
    8. Always keep the seawater valves closed when the engine is not running, while the boat is in the water. This will prevent flooding and sinking. Be sure overboard check valves work properly.
    9. Fuel oil dilution is a major cause of engine failure. Leaking jumper lines and unit injectors are the biggest causes of fuel oil dilution. Operating the engine for short periods of time could also cause fuel oil dilution.
    10. If the boat is stored in the skids, be sure to remove the bilge plug. If the bilge plug remains in place, the boat could fill with water and flood the engine.


  4. Cold Weather Operation
    1. When entering an area where freezing temperatures are anticipated or when ambient temperatures fall below 0O C, (32O F), problems can develop in operation and maintenance, e.g., cracked engine blocks, dead batteries, engines that won't start.
    2. Use of a mixture of antifreeze (ethyleneglycol) and distilled water should prevent freezing.
    3. Be sure the seawater side is drained, i.e., exhaust manifold, cooler, pump. Make sure the seawater pump is not frozen before starting.
    4. Batteries should be kept fully charged, because a discharged battery freezes at a higher temperature than a fully charged one.
    5. Much of the difficulty in starting diesel engines at low temperatures is caused by the high viscosity of the lubricating oil that causes low cranking speeds. If the viscosity gets too high, the pump cannot pump the oil and if the engine is started, the main and connecting rod bearings are likely to fail from lack of lubrication.
    6. At temperatures below 0o C (32o F), use JP-5 for fuel. When the outside air temperature drops by 10o F, cylinder temperature may drop as much as 20o F. Note: Most small boats always use JP-5.
    7. The cranking speed also determines cylinder temperature. MOST engines start most readily with the throttle fully opened.
    8. During periods of cold weather it may be necessary to use an ignition aid. This is because the colder air may not heat up enough on compression to cause ignition when the fuel is injected. The types of air heaters and primers used include the following:
      1. An air heater usually consists of a 1200 watt resistance grid mounted in the air intake manifold. It is powered from the starting battery before and during engine cranking.
      2. Ether primer is the most widely used. Use either the ether capsule or the pressurized cylinder type.
        1. The capsule type is only good for one start and then has to be replaced.
        2. Ether comes in spray cans also. Take care so that excessive amounts of ether are not used since serious damage to the engine may result.

      3. Flame primer is a widely used type of air heater. It is essentially a small oil burner with electric ignition. Fuel oil is sprayed into the air intake manifold and ignited by means of a spark plug, ignition coil, and vibrator. The principal advantage of the flame primer is that it imposes a negligible load on the starting battery. The unit is designed to fit into a hand hole cover plate near the center of the air box.

  5. Safety
    1. Ether is highly volatile, making it dangerous to carry aboard ship. Ether can kill if enough is taken into the body and could cause blindness if it gets into the eyes. Observe standard safety precautions as outlined in OPNAVINST 5100.19C (Safety Precautions for Forces Afloat) Chapter 10 and the NSTM.
    2. When checking battery electrolyte, the diesel must be secured. The maintenance person performing the check must wear safety goggles and rubber gloves.
    3. Refueling is a potentially dangerous evolution. When refueling of the boat must be accomplished, adhere to the following guidelines:
      1. Never refuel at night.
      2. Always make sure that the engine has been cooled at least thirty minutes prior to the start of fueling.
      3. Two man rule in affect. Always make sure that someone has been designated to standby as observer or to man fire fighting equipment.
      4. No smoking in the vicinity of the boat while refueling.
      5. No personnel will be in the boat while refueling is being done (other than the individuals required to actually refuel the boat).
      6. Appropriate fire fighting equipment shall always be standing by in the area of refueling operations.