Old Iron

28 08 2008

Today we’ll cover some of the realities of older engines that will help you decide the best route to take as your engine comes up for rebuild or replacement.

One of the most challenging aspects of using older diesel engines in a marine operation is managing part-load operation to avoid “wet stacking” and “fuel dilution” that can occur.

First though, let’s cover the terminology: “Wet stacking” is incompletely burned fuel, that has left the the cylinder through the exhaust valves. This fuel “paints” the inside of your exhaust manifold with a thick, black ooze. This fuel will soon will find any leaks in your exhaust system, and on the outside of the engine this fuel looks a lot more like lubricating oil, than diesel fuel. This appearance has even been the trigger for un-needed engine repair jobs. “Fuel-dilution” on the other hand is unburned fuel that goes down past the cylinder’s piston rings, diluting the lubricating oil with fuel,and reducing the viscosity of the oil.

Diesel engine ratings determine not only what an engine is capable of, but also the way it must be used. For example, an engine rated for generator use must carry a load that is no less than eighty percent of its maximum rating, eighty percent of the time, for best results.
Following this eighty percent rule, for example, a 100 kW marine generator set would not be allowed to produce less than 80 kW.
Conditions come up when there just isn’t enough load to put on an engine. One example of this would be a main propulsion engine that is rated at 400 horsepower (hp) at 2100 rpm, and the engine is periodically used to power hydraulics at only 700 rpm. A few minutes of this isn’t so bad, but  hours of producing only 20 hp, or five percent of its rating, will harm the engine.
Another example is a generator set engine that is rated at 60kW to power a vessel’s heavier electrical loads, but only produces 12 kW at night when the crew is using the electric range and doing laundry.
Plainly, some engines can tolerate part load operation better than others. There is a qualifier for this statement though; many, if not most diesel engine powered boat engines are ten to fifteen years behind the “State of the Art” in fuel efficiency. This list focuses on the older engines that are in the 20-500 horsepower range.
A list of general rules follows:
-Newer (technology) engines are better at part-load, than older ones. One good reason for this is the ongoing advances in engine design and materials. Another reason is that the ever more stringent emission standards are helping to insure that all engines do a better job of burning their fuel in the cylinder, and not in the exhaust manifold, even during light loading conditions.

-4-stroke engines handle part load better than 2-stroke engines, and one good reason for this is that there is more time for the fuel to burn before the exhaust segment of the combustion process.

-4-stroke engines with 3-ring pistons will do better than 2-ring pistons.

-Direct fuel injected engines, do better than pre-combustion chamber engines because the injection pressure is much greater and the fuel is more finely atomized.

-Air-cooled engines, sometimes do better than water-cooled engines at part load operation because the cylinder temperature of an air cooled engine tends to be 10-15 percent hotter.

-Electronically controlled engines, perform part load operation better than mechanically governed engines because electronically controlled engines usually inject fuel at higher pressures.  The electronic engine’s control system also, much more quickly, cuts back the amount of fuel injected as the load tapers off.

-Square-cut piston compression rings often work better for lightly loaded engines than the tapered Keystone-style rings. The reason for this is that square cut rings are not as dependent on cylinder pressure to force the rings against the cylinder wall during light loads.

-Naturally aspirated engines sometimes work better for light loads than turbocharged engines because their cylinder compression ratios are usually higher.

-Small bore engines, that is, the smallest bore engine that is sufficient for your application, work better than large bore engines because it is easier to control leakage in a small cylinder.Can we say then that the ideal marine diesel engine would be a technologically advanced, air-cooled, electronically controlled, 4-stroke, direct injected, naturally aspirated, with three-ring pistons and square cut compression rings?

Unfortunately there is no such marine engine in production. However, we can say that as engines are reconditioned or replaced we can keep the above attributes in mind, as part of a strategy to deal with part loading problems.
Finding the minimum “loaded” RPM for your model and series of your engine is important. Begin by getting the engine manufacturer’s guidelines. Every engine company that is involved with marine diesel engines also publishes an Installation or Application Manual. Next, pound the dock a little and check with those that use similar equipment under conditions like yours.
For main engines, eliminate all idling under 1200 RPM. For those hydraulic systems that run off of the main, changing the sizes of pulleys can let your main idle a little faster while your pump turns a little slower.
There are two ways to size generators for a fishing vessel. The first is to buy a gen set that will handle more load than you have. This works great for tired crews, because it doesn’t matter what order the loads are applied to the generator. It also works well if there is a smaller “hotel” gen set for cooking, lights and laundry. However, having just one large gen set can easily lead to light loads.
The second way is to do a very careful power survey and then install a smaller capacity gen set that will require sequential loading. The way this works is that the largest loads are put on the generator first and then the next largest and so on. This enables the use of a smaller set that can help to more easily manage the loading.

Vital Hand Tools For Your Boat

19 08 2008

Every boat needs a good set of hand tools, and a box to carry them. What are the minimum tools you will need on the boat? If you have room for a more extensive tool collection, what should you include?

Hand Tools For Your Boat

Hand Tools For Your Boat

We will answer these questions after discussing the Physics involved with hand tools on boats.

When we studied Physics in High School, Gravitational Force was well covered. Then our instructor broke his leg and we got a substitute teacher named Fred.

Fred was a recovering commercial fisherman and had later gone into teaching. He explained that on board boats there is one additional force at work that occurs nowhere else in the Universe: He called it the Bilge Force. He explained that on boats the behavior of Matter, the Laws of Physics, and even Time itself appears to behave differently than on land.

He warmed to the subject, “While gravity attracts everything, pulling it toward the center of the earth, the Bilge Force is selective and attracts only the things you need most, and pulls these items to the lowest, furthest, deepest, and darkest part of the bilge.” Fred also explained, “On land things fall straight down, but on a boat things fall diagonally, always toward the deepest part of the bilge water, and under the engine, just beyond arm’s reach.”

The Bilge Force is always the strongest between 10:00 P.M. and 2:00 A.M. local time, when marine mechanics happen to be the weakest.” And, “Yes, the Bilge Force always works in local time.”

So, first on your list of boat tools is a strong magnet!

Must Haves

To get an idea of the basic tools you need, consider what you will find if you look inside your local marine mechanic’s toolbox, the one he or she packs up and down the dock:

-A strong extendable magnet!!

-Straight screwdriver

-Phillips screwdriver

-An 8” or 10” adjustable wrench

-Slip-joint pliers

-Water-pump pliers (also known as Channel-lock pliers)

-Feeler gauges up to .035”

-6” dial caliper with inside, outside, and depth measurement capabilities

-⅜” drive socket set with both metric and standard sockets

-½” drive socket set with both metric and standard sockets

-Straight tin snips

-Electrical terminal crimping pliers

-Side-cutter pliers, also known as diagonal cutters

-Needle-nose pliers

-Battery terminal cleaner

-24-ounce ball peen hammer

-Standard combination wrenches from ¼” inch to 1⅛”

-Metric combination wrenches from 8mm to 19mm

-Standard Allen wrench set

-Metric Allen wrench set

-Universal filter removal wrench

-Center punch

-Cold chisel

-Gasket scraper

-Vise-grip locking pliers

-Multi meter with volt, amp and ohm capability

-Thread-locking compound, known as Loc-tite

-Never-seize compound

-Electrical tape

-Pipe thread sealant

-Penetrating oil

All of this in a fairly weather-proof box that is shaped more like a tray, to help you quickly spot what you need.

However, there are probably some additional hand tools you need on the boat that differ from those of the marine mechanic.

Would Haves

We’ll mention a few important additions to our basic list:

Left Handed Twist Drills. Boat maintenance often includes removing broken bolts that still have part of the bolt stuck in a threaded hole. When drilling-out broken bolts with regular right-handed drills, the drill will often “catch” in the piece being drilled and turn the broken piece even deeper into the threaded hole in which it resides. To get around this problem, it helps to drill out broken bolts with left-handed bits. Then when the bit “catches” it will spin the broken piece out of its threads. Remember to spray the piece you are drilling with penetrating oil to improve the odds on removing the broken piece.

Mechanical Fingers. When reaching deep into the bilge of a steel boat with a strong magnet, it seems that the magnet will stick to everything but the piece you are trying to pick up! Hand-operated mechanical fingers can be helpful at a time like this, and are readily available in most marine oriented hardware stores. The durable fingers of the tool are made of spring steel that can be straightened if accidentally bent.

Internal Pipe Wrenches. When removing sections of threaded pipe it often happens that the pipe wrench jaws squeeze the end of the pipe out-of-round. To avoid crushing the pipe, you can insert any round object that happens to fit snugly into the opening of the pipe before using the external pipe wrench, or you can buy an internal pipe wrench. An internal pipe wrench grips the inside of the pipe and tries to expand the pipe rather than crushing it as you tighten or loosen the section of pipe.

Crow-Foot Wrenches. For removing or replacing nuts that have a fuel or hydraulic line coming through the center of the nut, nothing works better than a crow-foot wrench. It can also be attached to a torque wrench for doing fine work.

Infra-Red Thermometer. The ability to quickly measure the temperature of engine and machinery is very important at times, such as when an engine is overheating.

An infrared thermometer senses temperature over distance and provides a gauge on the rear of the gun for a temperature read-out. The tool even has a gun sight or a laser for aiming the gun at what you want to check.

32-Volt Test Light. Testing a D.C. electrical system for voltage is often an important task and can be done quickly with a test light instead of a multi meter. This tool is handy because you can carry it in a shirt pocket and it will let you check for the presence of any voltage up to 32 volts with the same bulb. To get one, buy a 12 volt test light and then replace the bulb with a 32 volt bulb.

(Some of this material excerpted from “PRACTICAL BOAT MECHANICS”, by Ben L. Evridge, to be published this fall.)

Send your suggestions and we’ll add them to the list!

Recognizing Combustion Chamber Configurations

5 08 2008

Comparing Gas And Diesel Engine Combustion Chamber Locations

Comparing Gas And Diesel Engine Combustion Chamber Locations

This drawing compares the location of combustion chambers between many, if not all gas and diesel engines. This important difference becomes critical after an engine submerges or gets water, fuel, or coolant above the piston.

When an engine is hydraulically locked like this, there is a night and day difference between the two engine designs, and how to go about clearing the cylinder.

With the gas engine on the left, notice that simply waiting a while will allow most of the fluid to drain down through the piston ring end gaps, and eventually you will be able to rotate the engine. Or, to hasten the process, you can pull the spark plugs and turn the engine over.

Notice however, that the top of the diesel piston is constructed so that the fluid cannot escape unless the injector is removed and the engine barred over to clear the fluid.

(Some of this material excerpted from “PRACTICAL BOAT MECHANICS”, by Ben L. Evridge, to be published this fall.)

The First Ten Seconds

29 07 2008

F.V. Atlantico

F.V. Atlantico

If we could look inside a marine engine and watch what’s happening during the first ten seconds of a cold start, we might be surprised!

Over the life of an engine, eighty percent of the wear to engine bearings will take place as the engine begins to turn without lubrication, during cold starting.

When an engine is turned off, the lubricating oil slowly leaks from between the components that depend on the oil film and its wedge-effect. The oil wedge-effect is present when engine components are separated by lubricating oil, and there is sliding or rotational movement. However, when oil pressure ceases and the engine sits still for a little while, large pockets of air enter the lubrication system. This air must be eliminated by oil pressure once the engine starts. As the engine begins to turn, the oil pump quickly lifts a column of oil from the oil pan and goes about forcing all the air from the lubrication system.

When a 12-volt starter motor begins cranking a cold diesel engine-in the 300 horsepower range, voltage at the starter can drop from 13.8 volts to only 11. Amperage can go from zero to well over 1000 amps in an instant. The affects of the sudden electro-magnetic field around the starter cables may make them jump or seem to “crawl”.

The fuel system quickly begins to build high pressure for injection into the cylinders. The injectors begin forcing fuel into each cylinder; one at a time, in the engine’s firing order. Smoothly carried forward by heavy flywheel that keeps the crankshaft rolling on to the next cylinder in the firing order, and the next and the next…

Many mechanical governors go into the full fuel mode when the engine is off. This happens so the injectors will have a real “kick” for starting the engine. These same engines, equipped with a mechanical variable timing unit will also keep the engine injection timing fully retarded to aid starting. When the engine starts turning, each injector will be putting in near their full volume capability until the engine speed gets up to the governor’s pre-set low idle speed. At which point, the governor will quickly feather back the fuel delivery to maintain a steady low idle speed.

When the oil pressure comes, the crankshaft and the flywheel quickly rise to the center of their bores in the cylinder block and flywheel housing, both lifted and supported by the oil wedge. The oil wedge acts between the crankshaft journals and the engine bearings. It would not be far-fetched to say the crankshaft is “surfing” on a film of oil, at this point.

If the crankshaft main bearings have five thousands (.005”) of an inch oil clearance, then the presence of lube oil lifts the crankshaft and related components nearly half this distance, or approximately .0025”of an inch, to the center of their bore. This weight can be the several hundred pounds of steel and cast iron that the crank and flywheel consist of. If the engine has a front mounted power-take-off clutch, the oil film must lift this additional weight as well. On larger engines this total weight can exceed a thousand pounds.

The cold and dense column of air in the exhaust system begins to move, slowly at first, like molasses, as the engine turns and starts. The 400 degree F gases that are clamoring to work their way out from below have a much easier time flowing in, around and through the exhaust system. As the exhaust gases warm they expand, losing density, becoming much easier to pump up the stack.

The oil pump for the marine gear turns any time the engine crankshaft turns. Therefore, as the engine begins to fire, it must overcome the increasing power demand from driving all the so-called parasitic loads.

Parasitic loads are those loads (or work) that must happen in order for the engine and marine gear to run properly.

Suddenly, there is a demand for fresh air in the engine room, and lots of it, as all cylinders begin to fire!

We’ll let it warm up, and then it’s time to go fishing…

(Some of this material excerpted from “PRACTICAL BOAT MECHANICS”, by Ben L. Evridge, to be published this fall.)

F.V. Ocean Bay

F.V. Ocean Bay

Flywheel Housing Leaks On Generator Sets

25 07 2008

Fylwheel Housing Oil Leaks On Generator Sets

Fylwheel Housing Oil Leaks On Generator Sets

One of the more important maintenance items to watch with generator sets is the engine’s rear crankshaft seal. When the seal fails, engine oil leaks into the flywheel housing between the generator windings and the engine. A quick inspection of the air discharge end of the generator can tell if there is a build up of oil and dust. Oil visible in the flywheel housing should serve as a red flag signaling the need for maintenance.

The general drawing to the left here shows possible sources of oil leaks in the flywheel housing, however, most newer engines do not have wet bolt holes in the crankshaft or flywheel housing bolt holes.

Inside the flywheel housing are three things: 1-The drive plates that couple the generator shaft to the flywheel, 2-The engine’s flywheel, and 3-The engine’s rear crankshaft seal.

Generator engines normally turn at either 1,800 RPM or 1,200 RPM. Therefore, any oil that leaks past the rear seal is flung outward by the spinning action of the flywheel. The oil is then picked up by the air coming from the generator fan and becomes an airborne mist. This oily mist is carried throughout the generator enclosure because of the tremendous amount of cooling air that the generator fan moves through the generator. Many generator sets move between 500 and 1,200 cubic feet of cooling air per minute (CFM). This means that, in a small engine room, several times the volume of air in the enclosure can pass through the generator every minute.

Unfortunately, the oily mist re-circulates back to the air intake portion of the generator and is pulled through the generator again and again. This puts a uniform coat of oil on every part of the generator. The oily mist is also pulled into the generator engine’s air filter. In fact, any engines running nearby will draw oil into their air filters causing premature airflow restriction.

Oil on the generator windings acts as an insulator, slowing heat transfer. This will prevent the windings from being adequately cooled.

Speaking of generator winding insulation, other related problems occur when there is the least amount of water or salt spray coming into the generator air-stream. Even splash from bilge water, on board a boat, in rough weather can find its way into the air stream that is passing through the generator end. The problem here is that water contains minerals that will carry electrical current and can cause a short circuit if a crack develops in the winding’s insulation. Bilge water also carries microorganisms that eat the insulation from the windings in the generator.

In fact, generator winding insulation is degraded when anything other than cool dry air passes through the generator including dust, oil, fresh water, or saltwater.

At the first hint of a seeping rear seal, it’s time to find out if the seal has failed, or there is some other problem.

As you begin to troubleshoot the oil leak, first check the engine oil level to learn if the level is too high. A high oil level can cause even a good seal to leak. Someone may have filled the engine with too much oil. Or, perhaps the engine may be mounted at an extreme angle. It is also possible that you may need to check the dipstick calibration. Each engine maker has a suggested method for calibrating the dipstick. Refer to your engine manual.

Fuel or coolant leaking into the engine’s oil pan can explain a high oil level in the engine. Yet another cause of a rear seal leak is a restricted crankcase vent line. When pressure in the crankcase gets above two pounds per square inch (PSI) the rear crankshaft seal will usually fail.

Engines that have wet bolt holes in the flywheel-mounting flange can experience a leak through one or more bolt holes, too. Some engines also have wet bolt holes in the flywheel housing that can mimic a rear seal failure.

Note: A wet bolt hole is one that allows the bolt to thread into part of the engine that contains engine crankcase oil.

One more reason for rear seal failure occurs when an engine has many hours of service and the rear main bearing has worn excessively. In this case the crankshaft can wobble as it turns while the engine is being started. This wobble will cause the rear seal to leak. The rear main crankshaft bearing will often wear more than the front engine bearings because the engine must start dry with the weight of the generator’s revolving member hanging on the flywheel.

(Some of this material excerpted from “PRACTICAL BOAT MECHANICS”, by Ben L. Evridge, to be published this fall.)

Crank Main Bearings Wear More At The Flywheel End

Crank Main Bearings Wear

Plug That Critical Passage!

22 07 2008

Plug Critical Passages

Plug Critical Passages

When working around critical passages and scraping gaskets, be sure to plug the opening, as shown here. Next, scrape the gasket, taking care to work around the shop cloth. This practice will protect the engine from contamination.

Scraping The Gasket

Scraping The Gasket

Unplug The Passage When Finished

Unplug The Passage When Finished

(Some of this material excerpted from “PRACTICAL BOAT MECHANICS”, by Ben L. Evridge, to be published this fall.)

Four Important Ratios

22 07 2008

Ratio Of Steering Cylinder Travel To Rudder Arm

Ratio Of Steering Cylinder Travel To Rudder Arm

Remember these important ratios that make or break your boat’s handling.

1-Ratio Of Steering Cylinder-To Rudder Arm Travel: When steering components are changed or a new boat is built, the steering helm can require too many turns to steer the rudder from lock-to-lock to be practical. This will also greatly reduce the steering effort. Or, if the system has insufficient turns, the effort required at the helm can be far too high to be practical.

To remedy these conditions, move the point of connection to the rudder arm out if the effort is too high. If on the other hand the system requires too many turns, move the point of connection inward toward the rudder shaft, even drilling an additional hole if needed.

Ratio Of Engine Speed-To Transmission Output Shaft Speed

Ratio Of Engine Speed-To Transmission Output Shaft Speed

2-Ratio Of Transmission Output Speed-To Engine Speed: When a diesel engine turns at 2,000 rpm and the propeller shaft turns at only 1,000 rpm, it is said that the drive ratio through the transmission of 2:1. Put another way, 2,000 rpm is going into the front of the transmission but only 1,000 rpm comes out the back. This is accomplished by using two gears inside the transmission running together. From the ratio we can see that the driving gear, the one from the engine, must have half the number of teeth than those on the gear that drives the propeller shaft. The gear reduction is what allows the engine, transmission, and propeller shaft to work together to move the boat efficiently through the water.
3-Ratio Of Governor Lever-To Throttle Control Movement: The response of engine speed acceleration can be changed by altering the ratio of the control-to the throttle lever movement, as shown.

4-Ratio Of Transmission Shift Valve-To Travel Of Shift Control Movement: The same is true for the shifting mechanism.

Ratio Of Control Travel-To Engine And Transmission Levers

(Some of this material excerpted from “PRACTICAL BOAT MECHANICS”, by Ben L. Evridge, to be published this fall.)