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Can You Handle These 5 Common Boat Repairs?

Every boat owner will encounter at least one of these problems — at an inopportune moment, of course! Here's how to deal with them.

Servicing outboard engine

You don't need to know how to fix everything that could go wrong aboard, but a few simple skills could mean the difference between enjoying a fun day on the water or being stuck at the dock. (Photo: Getty Images/Amnat Jonjum)

There are few recreational activities that provide more opportunities to channel your inner MacGyver than boating. The key to successfully overcoming these impromptu lessons on how your boat systems work is having a plan in place before they occur. Let's look at five situations all boat owners should be prepared for.

1. Replacing A Worn Or Broken Alternator Belt

That squeal coming from your engine compartment is likely your boat's way of saying the alternator belt needs replacing. A belt that's beginning to disintegrate will show signs of fraying or cracking, which can usually be seen while in place with a flashlight and hand mirror. The presence of belt dust (a black dust or residue) in the front of the engine is a common sign of belt deterioration. It's also a possible indication of wear due to a misalignment issue. If you notice this, your inspection should also include use of a straightedge to verify all pulleys are square.


Go to for a handy step-by-step guide on how to adjust an alternator belt.

When installing a new belt, start by studying the old belt's routing if the belt is intact and still in place. Simplify things even more by taking a few pics for reference prior to removal. If the old belt has self-destructed, verify routing of the new belt by consulting the engine manual.


Photo: Mark Corke

Removing an existing belt or replacing a broken one will typically involve loosening some component, such as the alternator, then retensioning and tightening it after the new belt is in place. Once installed, use your thumb to apply moderate pressure halfway between the pulleys. The new belt should deflect around 3/8-inch depending on the distance between the pulleys. Follow your engine manual for specific guidelines.

2. Troubleshooting Electronics Issues

What's the plan if your depth sounder blanks out while entering a questionable harbor, or the chartplotter bites the dust when heading out for a day of fishing? The first step in troubleshooting a piece of electronics gear or system is something you've hopefully done before the problem arises: read the owner's manual. A basic understanding of how a system functions and is installed (e.g., a block diagram) before you start troubleshooting is extremely helpful in recognizing and locating common problems. Most manuals will also have a basic troubleshooting section, which can help point you in the right direction.

When a piece of electronics gear fails to turn on, start by checking the power connection at the unit for looseness or corrosion. If your DC power panel has a volt meter installed, take a quick look to verify that it shows the correct voltage and that all required breakers are on.

For electronics that work intermittently or lose certain functions, check the remaining plugs or wire connections. These could also suffer from corrosion or may have vibrated loose over time. Sometimes problems can be corrected by simply disconnecting cable plugs and plugging them back in. The same is true for inline cable connections, which can loosen due to excessive movement or vibration if not secured or mounted properly. Trace the cable run as well, while looking for breaks or other damage.

Poor wiring installation

Hopefully you won't encounter something that looks like this when you’re trying to track down the cause of an electronics issue. (Photo: Frank Lanier)

If a piece of electronics powers up but shows nothing on the display, start simply. Check the display brightness and contrast settings. These settings often get adjusted on purpose (to preserve night vision for example) or by accident to the point where the display is no longer visible under different lighting conditions. Other control features can also generate what I call "operator-induced anomalies." If your radar fails to pick up targets, for example, verify you're on the correct range setting and that the gain/sensitivity features are adjusted correctly.

When it comes to no-power issues, if you've verified all connections are tight, yet the problem persists, it's time to break out the multimeter. Every boat should have one, particularly as basic units can be purchased for less than $10. Stay away from light pen-type voltage testers, however. They can tell you if there's voltage, but not how much — a critical troubleshooting flaw as many electronics fail to operate if the voltage drops below a certain level.

To check the power to a piece of gear, turn the unit off and disconnect the power plug or access the terminal strip where power is connected. Then verify that battery switches and breakers are in the on position.

Set the multimeter to the appropriate DC voltage test setting (typically 12 volts DC, but you'll need to verify this). Many of the higher quality digital meters will auto scale to the correct voltage, eliminating this step.

Next, measure the voltage by connecting the meter's negative probe to the equipment plug negative lead and positive probe to the positive lead. If you accidentally reverse the probes, a digital meter will simply display a negative reading. A voltage reading of "0" indicates no power is reaching the unit. Common causes include a tripped breaker, blown fuse, loose connection, or broken wire. One thing to note is a fuse that "blows" multiple times when replaced should be considered a symptom rather than the problem itself.

A low voltage reading indicates low battery voltage or possibly additional resistance in the line (for example, a corroded or faulty connection). Verify that the correct amount of power is leaving the breaker panel, then work your way toward the equipment to identify the problem. If the voltage shown at the meter is incorrect, verify the voltage at the battery is correct and proceed from there.

Another factor to consider is how steady or consistent the voltage is during equipment operation. Some electronics draw more power during certain operations. A good example is your VHF radio when transmitting versus receiving. While you may have a "full" 12 volts at the power plug when the radio is disconnected or simply turned on, that voltage can drop well below a usable level when the radio is keyed to transmit. This is often due to a weak battery or possibly a corroded connection. Monitor your DC panel volt meter, or use your volt meter, while keying the radio to see if the voltage drops. (Whenever working around wires or electricity — even 12-volt DC — be aware of the issues and dangers, and the possibility of AC current in the proximity of where you're working. Avoid it if you're not familiar with what you're doing.)

Basic Repair Rules

  • Be prepared. Carry the proper tools, manuals, and parts for your systems.
  • Check the simplest things first, especially the last thing you may have adjusted or fixed. You may have inadvertently caused the current problem.
  • Take your time.
  • Troubleshoot your problem logically and methodically.
  • If you take something apart, stay organized. Take plenty of photos, mark larger items, and store small parts in labeled zipper-style bags for easy reference.
  • Don't be afraid to tackle a repair, or ask for help when needed.
  • Electrical problems typically boil down to something that's loose, wet, or has a dirty connection.
  • If something fails after completion of a repair or maintenance procedure, that's the first place to start troubleshooting.

3. Bleeding A Diesel Fuel System

Changing a fuel filter often introduces air into your fuel system. This air will typically have to be removed or "bled" from the system to prevent the air from blocking the flow of fuel to the engine. Air removal involves sequentially bleeding the fuel system at specific points.

Diesel marine engine

Have a diesel engine? You’ll need to know how to bleed it after you change the fuel filter. (Photo: Mark Corke)

Your owner's manual will outline the procedure for your particular engine, but here are the general steps:

1. Locate the engine lift pump and manual lever.

2. Loosen the bleed screw on top of the secondary filter (the smaller filter normally attached to the engine) while operating the pump. You only need to loosen the screw slightly, not remove it. Place a container beneath the filter beforehand to catch any spilled fuel.

3. Continue pumping until all bubbles are gone and only clear fuel weeps from the hole, then tighten the screw before you stop pumping.

4. Repeat the pumping procedure, only this time loosen the bleed screw (or fuel line fitting if no bleed screw is present) at the injector pump half a turn, then tighten as soon as clear fuel is ejected.

5. Locate the closest injector to the injector pump — the one with the shortest fuel line. Loosen the injector fuel fitting slightly and continue pumping until clear, bubble-free diesel runs out, then tighten. Repeat this process for each of the remaining injectors.

6. Try cranking the engine. If it fails to start after 10 seconds or so, go back and make sure everything is tightened properly.

4. Unclogging The Head

With the possible exception of, "Where's all this water coming from?" no statement strikes fear into a boat owner's heart quite like, "The toilet doesn't seem to be working." This is particularly true when you consider the issue typically doesn't make itself known until after "the deed" has been done.

The inability to pump the bowl clear is one of the most common marine toilet problems, and it almost always involves a clog or blockage. Somebody flushed something the system couldn't tolerate (no one ever fesses up, by the way) and here we are — an unpleasant situation with an even more unpleasant prospective solution.

For our purposes, we'll assume the toilet is a manual raw-water flush unit, the system most commonly found aboard small to midsized boats.

Unclogging head

Why does the head always wait until you're away from the dock to clog? (Photo: Frank Lanier)

Many sanitation systems will have a "Y" selector valve (above), which allows you to discharge bowl contents directly overboard or into a holding tank. Check to make sure the Y-valve is fully open — perhaps even work it a few cycles to verify proper operation.

If you're discharging overboard, at sea in an area where it is legal to do so, verify that the overboard discharge seacock is also open. If you are in a legal overboard discharge area and pumping into your holding tank when the problem occurs, you can also shift your Y valve, open up the overboard discharge seacock, and see if the system works. If so, you've just verified that everything from the toilet to the overboard thru-hull is operational and that the problem lies between the Y-valve and holding tank.

If you're discharging into a holding tank — a more likely scenario — and still unable to empty the bowl, make sure the holding tank is not full and that the holding tank vent hose isn't blocked. Insects like to build nests in the hose if the screen for the hull vent fitting is missing. I've also seen vent hoses clogged with bits of toilet paper or waste.

If the above items check out, yet the toilet handle is difficult to press down and you cannot empty the bowl, chances are you have a blockage in the discharge hose. Start by trying to blast the clog free using a household plunger. Just keep in mind it will only work in one direction, (i.e., the down stroke), due to the one-way valve or flapper (also known as a joker valve) installed at the toilet discharge to prevent waste from backflowing into the bowl. (Confirm with your manual that this method is OK.)

If the plunger method fails, it's time to gird your loins and get dirty. Rubber gloves, old clothes or coveralls, a stout length of wire (a fish tape or untwisted coat hanger) and a 5-gallon bucket are recommended weapons.

Start by disconnecting the hose at the toilet discharge outlet and running the wire down the hose. If you're lucky, you'll find the clog and break it free. Otherwise, it'll be trench warfare from here as you disconnect each successive hose section until the blockage is located and removed.

5. Changing An Engine Raw Water Pump Impeller

The best way to avoid the repercussions of impeller failure (overheating or the need to disassemble the engine cooling system to retrieve impeller pieces) is routine inspection and impeller replacement before failure. Many boaters simply replace the impeller during their annual inspection. It's cheap insurance, and you can keep those in good condition as emergency spares.

Impeller from water pump

Replacing an impeller is a fairly straightforward job. (Photo: Frank Lanier)

While you'll want to follow the instructions provided in your engine owners manual, here are the basic steps for replacing an impeller:

1. Close the engine raw water seacock.

2. Place a shallow pan or spread an old towel beneath the pump to catch wayward parts.

3. Remove the screws that hold the pump's cover plate.

4. Carefully remove the cover plate to expose the impeller. If the cover is stuck, gently pry it free, being careful not to bend or damage it. If the cover is distorted, scored, or has other issues, replace it pronto.

5. Remove the sealing O-ring or paper gasket, depending on the pump make and model. O-rings or gaskets in good shape can be reused in a pinch, but replacement is the best policy.

6. If the impeller has a rubber plug in the center, pry it out with a small screwdriver to see how the impeller is attached to the shaft. Most just slide on, although some may use a thru-bolt or set screw, which will have to be released prior to removing the impeller.

7. To remove the impeller, grasp two impeller vanes on opposite sides (using your thumb and forefinger) and pull/wiggle it out. If that doesn't work, try working it out using two flathead screwdrivers placed on opposite sides, being extremely careful not to damage the flat face of the pump housing. An impeller removal tool constructed of plastic (to avoid scratching the pump housing while prying the impeller out) is a good investment. Another option is using Channel-lock pliers to grip the impeller hub and wiggle it free.

8. Grease the vanes of the new impeller and the wall of the pump chamber. Most impeller kits will include a small tube of lube, but petroleum jelly also works. However, if this would damage your impeller (check manufacturer recommendations), glycerin may be better.

9. Slide the impeller onto the shaft. Folding the vanes while inserting it with a slight twisting motion may make this easier. Installing the vanes in the proper direction is best, however they'll arrange themselves regardless with the first revolution of the impeller.

10. Push the impeller firmly into place, then (if present) tighten the set screw or reinstall the thru-bolt or hub plug.

11. Install the gasket or O-ring as per the impeller kit instructions, and screw the cover back into place.

12. Open the seacock, then start the engine. Check the exhaust for proper water flow. If no water is ejected within a few seconds, shut down the engine and investigate the problem. Check the pump and verify no leaks are present.

Tech Support

It's always helpful to keep technical support phone numbers handy for all of your onboard systems. Many boat owners or captains have them stored in their cellphones for instant use. Before making the call, make sure you can describe the symptoms of the problem and what troubleshooting steps you've already taken. Keep all equipment or system information on hand (e.g., model, serial number) before making the call. Tip: You can store all this information in your phone using Notepad, Notes, or other app. Some apps will even let you add photos of the parts.

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Frank Lanier

Contributing Editor, BoatUS Magazine

Capt. Frank Lanier is a SAMS Accredited Marine Surveyor with more than 40 years of experience in the marine and diving industries. He’s also an author, public speaker, and multiple award-winning journalist whose articles on boat maintenance, repair, and seamanship appear regularly in numerous marine publications worldwide. He can be reached via his YouTube channel “Everything Boats with Capt. Frank Lanier” and website