Practical Boat Mechanics: Commonsense Ways to Prevent, Diagnose, and Repair Engines and Mechanical Problems


Work-around solutions and emergency

repairs that will get your boat home when all

else fails

Practical Boat Mechanics belongs onboard every

boat that has a gasoline, diesel, inboard, or out-board


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Practical Boat Mechanics: Commonsense Ways to Prevent, Diagnose, and Repair Engines and Mechanical Problems

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Work-around solutions and emergency

repairs that will get your boat home when all

else fails

Practical Boat Mechanics belongs onboard every

boat that has a gasoline, diesel, inboard, or out-board

engine. This practical collection of fast fixes enables you to repair failed machinery with basic tools under adverse conditions. Designed and written for non-mechanics, it

also presents do-it-yourself maintenance procedures

and schedules that will prevent most problems from


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Product Details

  • ISBN-13: 9780071445054
  • Publisher: McGraw-Hill Professional Publishing
  • Publication date: 7/14/2009
  • Edition number: 1
  • Pages: 320
  • Sales rank: 1,438,506
  • Product dimensions: 7.20 (w) x 9.00 (h) x 0.80 (d)

Meet the Author

Ben L. Evridge spent 20 years maintaining

the 1,200 fishing vessels of Kodiak, Alaska, keeping them

running in one of the world’s most challenging marine environments. He is a regular contributor to National Fisherman.

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Read an Excerpt


Commonsense Ways to Prevent, Diagnose, and Repair Engine and Mechanical Problems


The McGraw-Hill Companies, Inc.

Copyright © 2009 International Marine
All rights reserved.
ISBN: 978-0-07-144505-4




Before you begin caring for your boat's mechanical health and diagnosing and treating its mechanical symptoms, you should meet the patient. Chapters 1 through 9 offer a tour of your boat's mechanical mysteries and make a number of suggestions for routine maintenance. Caring for your boat's mechanical systems is not only the best way to keep them functioning reliably, it's also the best way to learn how they function and to prepare yourself for problem solving if and when something does go wrong.

This chapter covers a few of the basics. Your boat may be brand-new, it may simply be new to you, or it may be a mechanical mystery even though you've owned it for several years. Whatever the reason, it's time to meet your boat and to familiarize yourself with a few of the techniques and circumstances you'll encounter again and again as you work with mechanical systems aboard.


Before you use your boat, gather the information and make the inspections noted in this section. You need to be familiar with all the important systems on board to properly maintain them and to know what to do if something goes wrong. You'll be able to respond more quickly if you do your homework ahead of time.

1. Record the information from all engines and transmissions. Note: The transmission, which conveys engine power to the propeller shaft, is often called the marine gear, the gearbox, or simply the gear.

Every engine and transmission leaves the factory with a serial number plate (Fig. 1-1) to enable the ordering of parts and service work. Most often these plates are attached with four small rivets. This same plate often provides the engine's power rating as well.

If no serial number plate is visible, begin looking for its original place on the cylinder block. You'll know you've found it when you see a flat rectangular area roughly two inches by three inches in size, framed either by four chiseled- off rivets or by the epoxy glue that once held the plate. When this is the case, you will have to get serial number information from the boat's previous owner. If this is not possible, an experienced marine mechanic can inspect the equipment and determine what was stamped on the plate.

If the plate is missing and there is no other way, it is worth hiring a mechanic to get you the information that was stamped on it. Don't be tempted to just let it go. You'll need the model and serial number whenever you call a mechanic for help. Your mechanic must have accurate information to know how your equipment is configured, especially if he or she hasn't worked on that type of engine or transmission before. It's also vital information when ordering parts.

2. Determine if the boat's transmission has a come-home feature. If it does, know how to engage it. This information will be found in the transmission service manual. (See also Figure 14-3 and Chapter 6.)

3. Locate and clean the transmission oil suction screen and filter, if so equipped. Most hydraulic transmission clutch failures start with a plugged suction screen. A failure is easy to spot early by monitoring any accumulation of metallic debris in the suction screen.

4. Find and check the oil dipsticks for both the engine and the transmission.

5. Learn how to check the coolant level (Fig. 1-2), and in cold climates keep track of the level of protection provided by the antifreeze. The coolant should be protected from freezing at temperatures as much as 20°F colder than the expected local minimum temperature.

In addition, you should monitor the coolant conditioner, an additive that minimizes the possibility of galvanic corrosion in the engine. You should do this in warm and cold climates. Fuel supply docks and most auto parts stores sell coolant test kits.

A large part of cooling system maintenance involves keeping the pH of the coolant slightly alkaline instead of acidic. Acidic coolant acts as an electrolyte, conducting corrosive currents between the dissimilar metals that exist in any engine's cooling system. Such currents, if unchecked, can cause galvanic corrosion that destroys metal and any non-silicone rubber coolant hoses.

6. Check the engine's direct current (DC) electrical system, including the starter motor, alternator, batteries, starter switch, the DC breaker or fuse panel, the engine and transmission gauges, all interconnecting wires, and often electronic engine and transmission controls. Note: If your boat has an AC system as well as DC, the two electrical panels are probably next to each other. Do not under any circumstances poke around behind an AC panel unless you know with absolute certainty that no power is flowing to the panel from a shore connection or from an onboard generator set. If you have any doubts about your ability or the system, call a marine electrician.

Write down the part numbers and operating voltages for the engine's starter motor and alternator. Also record the starter motor's direction of rotation (abbreviated on the starter motor plate as DOR or sometimes DIR), which will obviously be either clockwise (CW) or counterclockwise (CCW). Note: Alternators don't care which way they turn.

Next, find the boat's battery selector switch or switches. There are two different styles—the kind that can be switched with the engines running, and the kind that cannot. If your switch has two small wires running to it in addition to the battery cables, then it is the type of switch that can be operated (or turned) with the engine running. If there are no small wires running to the switch, then it must not be turned with the engine running. Failure to observe this limitation will result in destroying the alternator. The boat may even have both kinds of switches.

7. After turning off any battery chargers (called constavolts in some parts of the U.S.) and all electrical loads, check the electrolyte levels in all liquid-electrolyte batteries with a good light. (This step does not apply to gel and absorbed glass mat, AGM batteries, which are also generically called sealed or no-maintenance batteries.) If a battery's electrolyte is below the top of the battery plates, add distilled water.

If the batteries are alike, with the same warranty date on each sticker, you have found a sign of good maintenance. Dissimilar batteries should be replaced by a matched set when it is convenient.

8. After turning off all battery chargers and loads, disconnect, clean, and reconnect all battery terminals. Inspect all battery cables for cracked insulation, which can result in short circuits or leak power to the electrical ground and discharge the batteries over time.

Also, check the ends of the cables by lifting an edge of the insulation and looking for green (copper) corrosion at the terminals. If corrosion is present, it may be a clue that the cable has been chronically wet or even submerged. If so, the cable must be replaced.

9. If your boat has a fire suppression system, find its sensors and controls and verify that the bottles are full. If you have any doubt about the system, have it inspected by a fire and safety professional. If your boat has fire extinguishers rather than a suppression system, verify that the extinguishers are fully charged, properly inspected, and properly secured in their brackets.

10. Assuming the boat has a diesel engine or engines, locate all valves for both sides of the fuel system (suction and the return). Note whether the fuel lines to and from the boat's fuel tanks are plumbed and valved to allow the engine or engines to pull fuel from the tanks on one side of the boat and send the return fuel to the other side of the boat. This type of system is only found on larger boats. It is used to adjust trim as fuel in a port or starboard tank is depleted. Note: If the fuel system is plumbed this way, then it is also possible to return fuel to a full tank and thereby overfill the tank, sending fuel out the tank's vent and causing a fuel spill. The Spill Guard by Herrington Marine Technologies stops fuel spills by alerting the crew with a flashing light when the tank is full.

11. Verify that all external fuel tank fill openings are properly sealed. If there is an O-ring seal on the fill cap, check it for visible damage and replace it if needed. This will help keep water out of the fuel. Likewise, find the fuel tank vents and be sure they are clear of obstructions.

12. Find the stuffing box (Fig. 1-4) and learn the best way to adjust it. The stuffing box is where the boat's propeller shaft exits the hull. The stuffing box contains the propeller shaft seal, and the job of the assembly is to keep the ocean out of the boat while allowing the shaft to turn. Most stuffing boxes are designed to admit a slow drip of water, which lubricates the shaft, and the purpose of adjustment is to obtain the proper drip rate. If the drip is too fast, the bilge fills with water; if it is not fast enough, the shaft overheats. Note: Newer boats are often equipped with so-called dripless propeller shaft seals.

13. Locate and check the condition of the boat's freshwater tank or tanks, and also look for leaky or damaged hoses or fittings. The boat's freshwater system should include a replaceable activated charcoal filter with an exterior label indicating the date it was last changed.

14. Find the best method for an emergency engine shutoff on your boat. See Chapter 2 for more on this.

15. Locate the bilge pumps and bilge pump switches (Fig. 1-5), together with their fuses or breakers. Bilge pumps have two possible settings—manual or automatic. Verify that each pump works properly on either setting.

16. Locate the engine cooling system's raw-water strainer and its valves, if so equipped. Check the freshwater (antifreeze) side of the system (Fig. 1-6) for evidence of leaks, damage to the plumbing, or chafing of these critical hoses. Replacing depleted sacrificial zincs is also important to prevent damaging galvanic corrosion. Check the zincs and replace them as needed.

17. Locate all openings that pierce the hull and check for visible leaks, signs of corrosion (Fig. 1-7), and adequate tightness of the related fittings and hose clamps.

18. Outboard engines: Check the engine mounting bolts for adequate tightness, fuel lines for kinks or chafing, and steering linkage for excess wear. Also, check all controls and electrical connections for any apparent damage before starting the engine. If the engine is a newer four-stroke outboard, remember that the intake and exhaust valves do need to be adjusted periodically. If the engine is a two-stroke outboard, confirm whether it has automatic oil injection or not. If not, you will have to mix the oil into the fuel with each refueling. Read the engine manual to find the mixing ratio and the type of oil to add to the gasoline. Stock plenty of two-stroke oil on the boat.


The previous section showed you what to check on a boat you are just getting to know. At the risk of some redundancy, here are procedures to follow each time you start your gasoline or diesel engine(s) to ensure long, trouble-free service:

* Check the engine and transmission oil levels.

* Check the coolant level.

* Remove the cover from a vertical

dry exhaust stack, if your boat is so equipped.

* Check the battery charge.

* Now crank and start the engine(s), keeping your eyes on the oil pressure gauge to verify that the oil pressure is correct.

* Inspect the engine and transmission for leaks and excess noise.

* Idle the engine up to 1,000 rpm in neutral.

* Make note of the exhaust sound, and note the exhaust gas color; it must not be white.

* Unless your boat has a dry exhaust, make sure a healthy flow of cooling water is coming out with the exhaust.

* When the water (coolant) temperature reaches 100°F, you can put the engine into gear and idle away from the dock.

* When the water (coolant) temperature reaches 180°F, you can throttle up the engine to cruising speed.


This section is not meant to list a complete inventory of the tools you might need aboard. The focus is on a few items that have repeatedly proven their value. Here they are:

1. Jumper cables

2. A multimeter (electrical tester), along with the knowledge to use it (Fig. 1-9)

Note: NAPA auto parts stores sell an excellent booklet that explains how to test electrical items with a multimeter. Strangely enough, it is titled Burn Baby Burn, and it explains why so many electrical components are needlessly replaced due to ignorance of good electrical testing procedures.

3. LED flashlights

4. A shut-down paddle for stopping a runaway engine (see page 15)

5. Left-handed drill bits and Easy-Outs for removing broken bolts (see below)

6. A battery-powered Dremel tool (die grinder) and battery-powered carbide burrs (rotary files)


In addition to the foregoing, the following materials, spares, and fasteners may come in handy. They are so easy to carry that it would be a shame not to have any of them should the need arise.

1. You should have conversion charts to switch measurement units for bolt- tightening torque and for any other application.

2. Ultra-Gray Silicone Sealer is heat resistant and is especially useful because it sets up very firm. Good silicone sealants will replace many paper and fiber gaskets.

3. Rolls of gasket paper in various grades and thicknesses are essential for maintenance and repairs. Both 1/32 and 1/16 inch are good thicknesses to have on the boat. In a pinch, however, a temporary gasket can be made from cereal box paper. Just cut open a Cheerios box and cut the gasket's shape from the paper, then put a light coat of silicone sealer on both sides and install. In addition, any paper suitable for a gasket will also make a good shim.

4. Speaking of shims and shim stock, remember that some shims must be made of metal, such as steel, stainless steel, aluminum, brass, or copper. In a pinch, aluminum pop cans make a good shim. Galvanized and stainless steel stove pipe are also commonly available and make good shims.

5. Marvel Mystery Oil is an "upper cylinder lube," which means it is a good lubricant for valve guides and piston rings. It is available at most fuel docks and auto parts stores and can be added to both the engine lubricating oil and the fuel tank for use with either a gasoline or diesel engine.

6. It's important to carry both stainless steel and high-strength bolts and hardware on oceangoing boats. Engine bolts and fasteners, such as those that mount the alternator, are high-strength. In the United States, a high-strength bolt such as one of the ones attaching an alternator to an engine is called a Grade 8 bolt in the hardware and auto parts stores that sell them.

Spare fasteners come in ready-made kits from marine suppliers, or you can buy a case with many compartments and make your own selection. Other boaters will have good suggestions based on their own experience.

7. Carry spare oil pressure and water temperature gauges and senders (Fig. 1-10). Engines have been rebuilt when all that was wrong was a failed oil pressure sender that showed no oil pressure. At the first sign of high water temperature or low oil pressure, be sure to consider a failed sender. On the other hand, you should definitely consider that the gauge is accurate until you know otherwise. Trust but verify; verify the alarming readings with mechanical gauges that provide a reading with no electrical input.

If you don't have mechanical gauges installed on the engine, consider carrying pressure and temperature test kits. These kits are available from Snap-on Tools.

8. Carry high-quality black and red electrical tape for insulation purposes and for marking positive and negative electrical conductors.

9. You'll want to carry assorted sizes of crimp-on electrical terminals and heat-shrink tubing. The latter is plastic tubing that shrinks around electrical wires when heated. Small electrical supply kits are available at auto parts stores and offer a good assortment of terminals and heat-shrink tubing.

10. Aquarium-grade silicone sealant is handy to have for emergency repair of the boat's drinking water plumbing. If it won't harm fish, it won't harm you either!

11. Thread-locking compound (Loctite) keeps bolts and nuts from vibrating loose and is highly useful stuff to have around.

12. Spare engine-cooling system thermostats are important to have when an engine is running too hot or cold.


Know how to do the following routine procedures:

* crimp electrical terminals

* adjust your engine's valves

* adjust the fuel injection timing

* replace the water pump

* change the engine and transmission oil and filters

* change the engine air filter

* drain water from the fuel tanks

* switch from one fuel tank to the other while under way


There are a few emergency topics you should consider at length well ahead of time. If you do your homework regarding these potential problems, odds are you'll never have to apply the knowledge. If you don't prepare for them, you know how Murphy's Law works.

1. First, unless your diesel engine is self-bleeding, learn the procedure for bleeding air from its fuel system.

Note: All gasoline engines and some diesel engines have self-bleeding fuel systems.

2. Learn the procedure for bleeding air from your engine's cooling system after the coolant has been drained and refilled.

3. Know all the possible sources of water that can sink or damage your boat, and know how to halt each one.

Excerpted from PRACTICAL BOAT MECHANICS by BEN L. EVRIDGE. Copyright © 2009 by International Marine. Excerpted by permission of The McGraw-Hill Companies, Inc..
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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Table of Contents

Part 1 How Boat Things Work
1. ”Meet Your Boat”
2. Getting Familiar with Marine Engines
3. Cooling Systems
4. Belts and Hoses
5. Fuel, Lubricating Oil, Filters
6. Drive Train and Power-Take-Offs
7. Marine Electrical Systems
8. Exhaust Systems
9. Marine Steering
Part 2 Troubleshooting
10. Conventional Troubleshooting
11. Troubleshooting by the Five Senses
12. Gasoline Engines, Inboard & Outboard
13. Cabin and Engine Room
14. Marine Gear and Drive train
15. Steering and Controls
Part 3 The Resourceful Boat Mechanic
16. Crack Detection, Pressure Testing
17. Engine and Shaft Alignment

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