How to Keep Mice and Rodents Off Your Stored Boat

Indoor storage is the strongest defense, but a building with mice already in it is not. Outdoors, park on pavement or gravel rather than in tall grass, and keep the boat away from woodpiles, fields, dumpsters, bird feeders and stored feed or seed. Discover Boating points out that raising the boat off the ground helps, because rodents live mostly at ground level. Keep weeds and grass trimmed around the trailer through the winter.

Take off all snacks, wrappers, drink cans, pet food, birdseed, fishing bait and fish food. Check the glove box, console, cooler, livewell, tackle trays and the pockets of jackets and life jackets. Wipe down surfaces and vacuum crumbs out of carpets and seat bases (before any rodents arrive). Empty and rinse trash cans.

Cushions, towels, blankets, paper towels, toilet paper, rags and bimini boots are all ready-made nest material. Discover Boating recommends removing cushions and upholstery and storing them separately; if they must stay aboard, put them in sealed plastic bins. Store life jackets dry and indoors, and check them in spring before you rely on them.

Walk around and under the boat with a flashlight and look for any opening of about 1/4 inch or more:

• Drain plug hole and scuppers (on a boat stored ashore with the plug out)
• Engine compartment vents and blower vents
• Rigging tubes and cable pass-throughs for steering, throttle and wiring
• Gaps around the outboard rigging boot, bilge pump hose outlets and through-hull fittings
• Anchor locker, hatches and storage lids that do not close tightly
• Loose spots in the cover or shrink wrap, including vents and zipper doors

UC IPM recommends coarse steel wool, wire screen or metal for plugging holes, and warns that plastic screening, rubber, vinyl, expanding foam and wood are useless because mice chew right through them. Steel wool rusts when wet, so copper or stainless mesh or 1/4-inch hardware cloth lasts longer around a boat.

• Stuff mesh into rigging tubes and cable openings around the wires, without kinking or cutting anything.
• Cover vents with hardware cloth instead of blocking them, so the boat still breathes and does not grow mold.
• On a boat stored out of the water, a loose wad of mesh in an open drain hole lets water out but keeps mice out.
• Never plug engine exhaust, vents or drain holes in a way you might forget in spring. Hang a bright tag on the helm listing every plug you added, and remove them all before launch.

Discover Boating stresses ventilation to avoid mold and mildew, but vents must not be big enough for a mouse. Use cover vents with screens, close the shrink-wrap door completely and tape any holes. Tuck straps and tie-downs so they do not hang to the ground as ramps.

• Ultrasonic and electronic repellers: UC IPM says there is little evidence that sound, magnetic or vibration devices drive mice out or keep them away. They also need power, which a stored boat usually should not have running.
• Peppermint oil and dryer sheets: these show up on many boating lists, including Discover Boating's, but they lose their scent quickly and are not proven. Many owners report mice nesting right in the dryer sheets. If you use them, treat them as an extra, not your main defense, and replace them on every visit.
• Mothballs: do not use them. UF/IFAS Extension explains that mothballs are pesticides labeled only for clothes moths in tightly closed containers. Using them on a boat is off-label (illegal), the fumes build up in a closed cabin and can make people and pets sick, and they soak into upholstery.
• Rodent-deterrent wire tape and sprays: Discover Boating suggests these for wiring. They can help on exposed harnesses, but they do not replace sealing the way in.

UC IPM calls snap traps a great first step and the preferred method where only a few mice are present. They are cheap, you can see when they work, and they do not leave poisoned mice dying inside the boat.

• Set traps along walls and hull sides, in dark corners, in storage compartments and anywhere you see droppings. Mice run along edges, so put the trigger end against the wall.
• Use several traps, spaced close together. Peanut butter is a common bait.
• Put traps inside covered trap boxes or closed compartments so pets, kids and birds cannot reach them.
• Check traps on every visit. A trapped mouse left for weeks will smell and attract more pests.
• Battery-powered electronic traps also work, but must be checked and emptied just as often.

Rodenticides are risky on a boat:

• A poisoned mouse usually dies somewhere hidden, often deep in a compartment or under a deck, and the smell can last for weeks.
• The US EPA notes that most rodenticides are anticoagulants that take days to kill, and that the strongest ones are restricted to professionals because they threaten pets and wildlife that eat poisoned rodents.
• Consumer rodenticides now come only in ready-to-use, tamper-resistant bait stations, and each label says exactly where the product may be used (for example, indoors only, or outdoors within 50 feet of buildings). If the label does not cover your situation, do not use it.

If you have a real infestation in a storage building, call a licensed pest control company rather than scattering bait yourself.

Once a month if you can, lift a corner of the cover and look and sniff. Signs of mice are droppings (small, dark, rice-sized pellets), fresh gnaw marks, shredded paper or foam, and a musky odor. Empty and reset traps, replace any scent deterrents and re-seal anything that has opened up.

If you find signs of mice in spring, follow the CDC cleanup method:

1. Open hatches and the cover and let the boat air out for at least 30 minutes; stay away while it airs.
2. Put on rubber or plastic gloves.
3. Spray droppings, urine and nests with an EPA-registered disinfectant or a fresh bleach solution (1 part bleach to 9 parts water) until very wet, and let it soak about 5 minutes or as the label says.
4. Wipe up with paper towels, bag everything, then disinfect hard surfaces.
5. Wash your gloved hands, remove the gloves, then wash your hands with soap and water.

Do not sweep or vacuum droppings: that throws contaminated dust into the air. For a heavy infestation, consider a professional cleanup.

With the battery switch still off, go over everything rodents could reach:

• Wiring behind the dash and inside the console, under the helm and along the gunwales
• Harnesses at the engine, the trim pump and the battery area
• Bilge pump, float switch and navigation light wiring
• Fuel hoses, the primer bulb, vent hoses and water hoses
• Engine air intake, flame arrestor or silencer and any open cavity where a nest could hide
• Upholstery foam and carpet under seats
• Electronics cables: Discover Boating suggests tracing each one as far as you can from the screen to its power supply and to the transducer, at layup and again at launch

Look for nicked or stripped insulation, exposed copper, chewed connectors and nests. Remove any nest from an air intake or flame arrestor before starting the engine.

• Small nick in insulation, no copper showing: cover with heat-shrink tubing or quality electrical tape, and keep an eye on it.
• Exposed or cut copper: repair with marine-grade tinned wire, sealed crimp connectors and heat shrink, matching the original wire size. If you are not comfortable doing that, have a technician fix it.
• Damaged harness, many chewed wires or anything at the engine computer: this is a job for a pro.
• Chewed fuel line or primer bulb: replace it with the correct marine-rated hose before the engine runs.

Once everything is repaired, reconnect the battery, test every circuit and, on an inboard or sterndrive, run the bilge blower before starting. Note what you found in your BoatMend log so you know where mice got in.