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7 Hidden Boat Maintenance Problems And How To Fix Them

A few routine checks will go a long way to keeping you safe on the water. Here's what you could be missing.

Testing boat engine

Checking "under the hood" could save you from having a bad day on the water, or worse.

There's a lot of traditional land-based wisdom out there that just doesn't ring true for the maritime side of things. "Let sleeping dogs lie," "out of sight, out of mind," and "what you don't know can't hurt you" are all prime examples of advice not to heed when it comes to boat maintenance. This is a topic where an ounce of prevention is truly worth a pound of cure. In efforts to protect you from the old wives and their tales, here's a list of seven often-neglected items that can ruin your boating day quicker than "stepping on a crack can cause you to cry over spilled milk."

Stuffing Box

Where it is and what it does: Only boats with inboard engines have stuffing boxes. To locate yours, trace the propeller shaft from the transmission to the point where it exits the hull. That's where your stuffing box will be (unless you have a newer, dripless-style shaft seal). The purpose of the stuffing box is to allow the prop shaft to exit the hull while keeping water out.

Leaking stuffing box

An excessively leaking stuffing box will fling water all over the engine room and make engines, transmissions, and other components brown with corrosion.

The shaft is sealed by compressing packing against it, most often by using a hollow nut that screws onto the inboard side of the shaft tube or a tightening arrangement that uses a plate secured by nuts and studs on either side of the shaft. The more you tighten either type of gland, the more the packing material is compressed against the shaft. Most packing consists of a square plaited material and comes either as traditional greased (or waxed) flax, or a more modern version impregnated with Teflon.

What you should know: Water helps lubricate the packing material, so it's OK for a stuffing box to leak a few drips (three or four per minute) while the vessel is underway. More than that amount, say 10 drops per minute, or it drips while the shaft is not turning, indicates the need for maintenance. A leaking stuffing box can cause a number of issues, from corrosion caused by the spinning shaft slinging excess water all over your engine compartment to sinking, particularly if the boat is left unattended in the water for longer periods of time.

Packing material hardens over time as the lubricant dries out and gets worn away by shaft rotation, allowing water to pass and enter the vessel. When this happens, the first reaction is often to simply tighten the packing nut(s) to compress the packing material and stop or reduce the leak. This works to a point, but as the packing gets smaller it also gets harder. Keep compressing it and it will eventually score the propeller shaft, which will then have to be replaced before the stuffing box will seal properly.

How to Replace or Install a Dripless Shaft Seal/Stuffing Box

What you should do: You can avoid excessive leaking and shaft damage simply by replacing the packing on a regular basis. This bit of routine maintenance should only take about an hour, and it normally costs less for materials than you'd spend on a mocha-frappu-latte-whatever and a free-range muffin. How often you repack depends on the number of hours your boat is used. As it requires the boat to be out of the water, many owners simply repack the stuffing box as part of their annual haulout or spring commissioning routine.

Anchor Rode

Where it is and what it does: While the anchor typically enjoys a place of prominence at the bow, the anchor rode itself is relegated to the dark, dank recesses of the anchor locker. In a nutshell, its purpose is connecting the boat to the anchor. The anchor rode not only has to be strong but also possess at least some degree of stretchiness to absorb the effects of wind and waves. This helps prevent surge damage to the attachment point on the boat while reducing the chance an anchor will be ripped free from the bottom when it's needed the most.

Bad anchor rode splice

You may need to rely on your anchor in an emergency. If your chain-to-anchor line looks like this, it’s probably time to buy a new rode and correctly splice it to the chain.

What you should know: Most boats use a combination rode, which is simply a rope rode with a short length of chain between it and the anchor. You can attach your rope rode directly to the anchor, but it's not recommended. That length of chain protects the rope portion of the rode from chafe while adding weight, which increases horizontal pull and helps the anchor to remain set. Three-stand nylon is the most common type of line used. It's strong and provides more elasticity than braided line. It's also more easily spliced and cheaper.

Add Anchor Chain for Better Holding + Seizing or Mousing the Shackle

What you should do: Your anchoring system is only as strong as its weakest component, which includes not only the rode, but also shackles, splices, chains, mooring bitts, cleats — in short, any gear used to secure your boat while at anchor. Proper maintenance includes inspection of these as well as pulling the rode from the anchor locker and laying it out for thorough examination at least annually. Check rope rodes for issues such as wear, cut strands, aging, discoloration, and hard spots (due to heat generated friction caused by placing a kinked line under load). Chafe is a rope rode's worst enemy, so you'll also want to check hawseholes, chocks, cleats, windlasses, and other areas of potential chafe for burrs, sharp edges, protruding hardware, or anything else that can cause rode damage.

Outdrive Bellows

Where it is and what it does: Outdrives have flexible gaskets or rubber "boots" called bellows. Similar in appearance to an accordion, they seal out water around the exhaust, universal joint, and shift cable while allowing the drive itself to pivot and tilt while underway.

What you should know: Outdrive bellows can dry out and fail due to a number of reasons, from heat, extreme weather, and age. They can also be cut or torn due to marine growth such as barnacles, mussels, and other critters. Cracks or splits often occur inside the folds of the bellows. These can be difficult to see unless the drive is raised or tilted to the left or right (depending on the type and location) so that the bellows can be fully extended for inspection. A damaged bellows can cause damage to output shafts and gimbal bearings (due to water-induced corrosion) and can even lead to sinking in some cases.

Damages outdrive bellows

Outdrive bellows can deteriorate and fail over time due to age, exposure to ultraviolet light, or physical damage caused by hard marine growth. This exposes the outdrive to water damage and may even allow water to enter the vessel.

What you should do: Inspect all waterproof grommets and bellows for tears, cracks, dry rot, and other damage, at intervals recommended by the manufacturer as part of your routine maintenance schedule. Inspection timeframes may vary among manufacturers, but twice yearly (at the beginning and end of the boating season) is a good start. You'll also want to follow the manufacturer's recommended replacement schedule for your bellows (regardless of appearance) to head off any failure-related issues before they occur.

Fuel Tank Fill Hose

Where it is and what it does: Fill hoses are attached to the underside of the fuel fill deck fitting, connecting it to your fuel tank.

What you should know: All hoses have a limited lifespan, and the fuel fill hose is no exception. Recommended replacement timeframes will vary among fuel hose manufacturers, but some call for replacement as often as every five years. ABYC (American Boat and Yacht Council) standards also call for flexible fuel fill hoses to be double clamped at each end with marine-grade stainless steel clamps and to be marked on the outermost cover with the manufacturer's name or trademark, year of manufacture, and application.

Bad fuel tank fill hose

In many cases, fuel fill hoses need to be replaced every five years or so. This one is well past its useful life and is allowing fuel to leak into the bilge — an extreme fire hazard.

What you should do: Access and inspect fuel tank fill hoses for leaks and deterioration as part of your vessel's routine maintenance program. Check that each end of the hose is properly clamped and that the clamps themselves are tight and free from corrosion. Replace older hoses (regardless of appearance) as per the manufacturer's recommendations.

Deck Coring

Where it is and what it does: Most fiberglass boats have cored decks, a construction method where a core material (marine plywood, end grain balsa, foam, or other material) is epoxied to/sandwiched between two layers of fiberglass. Due to the "I-beam" effect, cored construction is lighter and stronger than solid fiberglass of a similar thickness.

What you should know: Preventing moisture from entering a cored deck is crucial to maintaining its strength and integrity. Unless the deck has been damaged in some way, water intrusion is normally by leaking at deck-mounted hardware and fittings, such as cleats, fuel fills, or bow pulpit or stanchion mounts. Leaks into the coring are typically caused by a combination of failed (or lack of) caulking during hardware installation and improperly sealing exposed coring after drilling hardware mounting holes.

Coring and deck rot

The coring in the deck around this hawse­hole installation wasn’t properly sealed, and you can see signs of deck rot (shadowy areas) around it from water entering.

Depending on the core material, water entry into the coring can quickly lead to rot and delamination or separation of the coring from the fiberglass. Classic signs include decks that have a spongy feel when walked on or that ooze water from deck fittings.

What you should do: A good start is to remove and rebed (caulk) deck hardware every seven to 10 years as a routine maintenance item. Follow recommended methods. Another is to follow the cored deck Golden Rule: Seal the exposed edge of the coring with marine-grade epoxy when drilling and mounting hardware. If you're able to de-core the area around these holes, you can fill them with thickened epoxy and (once cured) drill through the "plug" of epoxy without fear of moisture entering the coring.

Electric Bilge Pump

Where it is and what it does: Bilge pumps are typically located at the lowest portion of your bilge, which makes sense as that's where any water that enters the hull would naturally gravitate. If you have multiple bilge compartments or isolated sections, you'll likely have more than one bilge pump. A bilge pump's primary job is clearing incidental water from the bilges, such as packing gland drips, rainwater, and other sources. While they can provide extra time to do stuff when taking on serious water (such as putting on life jackets or making mayday calls) don't confuse your bilge pump with an emergency pump, which provides much greater dewatering capacity.

Dmaged bilge pump

Damage like this is most often caused by winter freezing. A cracked case can be hard to spot but has rendered this pump useless.

What you should know: Just because a bilge pump is rated to pump a certain amount of water, say 500 gallons per hour, that doesn't mean it actually will. While testers in the lab may be able to squeeze 500 gph from a pump without a discharge hose and under perfect conditions, a number of constraints that make doing so in the real-world different story. One crucial factor that contributes to this reduced output is called "static head" — the vertical distance bilge water has to be pumped before it can be pumped out. Just 2 feet of static head can reduce the output of a 500 gph pump by half, while 15 to 20 feet might neutralize the pump entirely.


Read "Bilge Pump Capacity: Do The Math" to learn how to choose the correct size bilge pump.

What you should do: Test and verify operation of all bilge pumps at regular intervals (preferably every time you go out, but quarterly or semiannually at a minimum). Do this particularly if the vessel is kept in a slip. Testing should verify that water is being pumped overboard, rather than simply switching on the pump and listening for motor operation.

The best way to keep your bilge pumps working is to conduct routine maintenance before problems occur. The corrosive environment of the bilge is a harsh place for all things electric, so check all wires and connectors for corrosion, and use only marine-grade heat shrink-style connectors (no wire nuts or electrical tape joints). Pump disassembly for maintenance is normally straightforward, however some are more complex than others, so be sure to read all instructions carefully to avoid assembly mistakes.

Gasoline Engine Compartment Ventilation Ducting

Where it is and what it does: Located in the engine compartment, ducting provides the means of bringing fresh air into the engine compartment and evacuating any gasoline fumes to the exterior of the vessel.

Damaged ducting

If bilge blower ducting pipework is damaged, loose, or missing, it will not suck explosive vapors from the engine compartment.

What you should know: Gasoline fumes are highly volatile and a leading cause of marine-related explosions and fires. If your boat has an inboard gasoline engine, proper ventilation of the compartment is crucial, both from a safety and legal standpoint. Federal law stipulates the use of a mechanical ventilation system (i.e., one utilizing a blower) for all non-open gasoline-powered boats built after 1981.

What you should do: Inspect the ducting regularly for splits, tears, blockages, crush points, and loose connections. Ensure the air intake ductwork is permanently secured to a point at least midway to the bilge or below the engine carburetor and that the exhaust ductwork end is permanently secured in the lower one-third of the compartment as far as practicable below the engines but above the normal accumulation of bilge water. Ducting installation must also be self-draining in the event water enters the ducting.


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 industry. He’s also an author, public speaker, and multiple award winning journalist whose articles on seamanship, marine electronics, vessel maintenance, and consumer reports appear regularly in numerous marine publications worldwide. He can be reached via his website at