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Pest Control Tips For Boaters

Waging war on the wildlife that takes a shine to your boat can pose big problems. Here's firsthand advice.

Sea gulls

If you want to keep birds off your boat, the best deterrent is not feeding them. (Photo: Getty Images/Zoom-Zoom)

Some years ago, on a fine Saturday morning in May, we drove down to our boat with the intention of spending the weekend cruising the Chesapeake Bay. It was to be our shakedown cruise of the season — you know, that one you look forward to and plan all winter?

Our previous summer's boating season had been cut short by major problems with the port engine, which had taken to billowing black clouds of smoke whenever we turned it on. This season, after large wads of cash had been imparted to diesel mechanics, we were nervous the problem hadn't quite been resolved. So there was a lot riding on this first weekend. After spending the previous weeks scraping and bottom painting, commissioning the engine, splashing the boat, filling the tanks, and settling her into her summer slip, it was finally time for the first foray of the season. We planned to anchor out that Saturday night and cook under the stars in gorgeous spring temperatures.

We spent an hour or two undoing canvases, loading weekend supplies, and getting portable electronics reinstalled. Just as it was time to cast off the lines, I went hunting for the stowable chart table we used on the bridge. Diving under the canvas on the back deck, I made an unsettling discovery. Inches from my nose, my widening eyes met another's. I dropped the canvas in fright, then lifted it again, slowly. She sat there still as a stone. We had a duck aboard, and judging from the elaborate nest she'd created for herself, she had no intention of going anywhere fast.


Our technical editor, Tom Neale, says you’ll never meet someone with a rat on their boat. Visit this article to read why "Mariners' Superstitions?".

I'm Irish, so superstition is a given, and I didn't want to risk bad karma with our already limping engine. Plus who doesn't have something of a soft spot for hard-working single moms? Ed suffered no such issues. His first thought was to throw her and her feathered, squatting behind off the boat.

"Evict her?" I shrieked, wanting no part in such bailiff bullying. This rising conversation all took place less than 3 feet from the duck, her privacy contained behind the canvas but her ears no doubt on full alert.

By now it was mid-afternoon, too late to get to our anchorage before dark, and the whole weekend's plans were rapidly unraveling. I reasoned there'd be many more trips where we could make up for lost time. Ed silently fumed. But realizing there was no budging Mrs. Duck (without looking to me like a heartless animal hater), he desperately scoured the internet for solutions. We called the SPCA, consulted with others on the dock, and asked colleagues about what we might do to move the duck without sacrificing the family she seemed so determined to raise. There were multiple suggestions, none feasible.

After several weekends spent sitting on the boat at the dock, waiting for what seemed like the longest gestation in history, we came down one weekend and the ducks were gone. Ed flew the boat out of the slip far faster than was necessary. And the engine? It ran like a breeze all summer.

"Chews" Your Insurance Wisely

Marine insurance policies typically exclude damage caused by "vermin." That said, if an animal chews through an exhaust hose and the boat sinks because of it, the GEICO insurance policy will pay for consequential damage caused by the sinking but not for the damage to the exhaust hose itself. If your boat isn't insured by GEICO, check your policy language or with an underwriter.

Some pests like flies, ants, birds, and spiders, may be an inconvenience. Rodents, on the other hand, can do significant damage and may jeopardize your boat. Rats and mice, particularly, like to nest inside boats laid up for the winter. Once aboard, they can chew through wiring, upholstery, and even woodwork, so check your boat regularly. If an infestation is suspected, deal with it right away — or call an expert.

An inspection of our marine insurance claims files shows that a significant number of boats that sink at the dock do so because muskrats have set up home inside the boat. That's right, muskrats! Native to just about every region of North America, muskrats are adaptable creatures and can be quite large; adults can weigh more than 4 pounds and have long claws and sharp teeth. Muskrats build burrows in riverbanks and shoreline areas, often the very same places where boats are kept. The exhausts of inboard-powered boats are appealing to muskrats as ready-made nesting sites.

One insured member fired up the engines on his boat and looked over the stern to ensure that cooling water was being ejected. One side appeared normal, but the other showed a distinct lack of exhaust and cooling water even though the engine temperature gauge indicated nothing wrong. When he lifted the engine room hatch, he found the problem: A muskrat had chewed a hole through the exhaust hose allowing exhaust gases and cooling water to flood into the boat. The owner was lucky; had the hose been eaten through on the waterline, the boat would have sunk and likely ended up as a total loss.

Some owners who store their boats in the water during the winter block off the exhaust to prevent such problems. An old paint can of the correct size wedged into the exhaust may work, but for a longer-term solution, there are "muskrat guards", metal rings and bars that permanently attach inside the exhaust outlet that don't have to be removed each time the engine is started.

— Mark Corke

Birds: Drops, Not Quite From Heaven

Turns out an extended number of the bird family are more than happy to take a perch or hover over your boat as though it had a flashing neon restroom sign on it. When it comes to outwitting them, the birdbrain tends to belong to the humans.

Pelicans on boat

Unwelcome guests can leave more than just a bad taste in your mouth. They can also damage your boat. (Photo: Susannah Clark)

Some years ago, BoatUS Magazine sent out a call asking readers what they'd done to discourage our feathered friends from choosing their boat. The results were large and varied. Unfortunately what seemed to work great for one boater had little effect for another, but clearly birds were a big problem. Marine supply stores sell many different items ranging from tape to bird-repelling spikes to a multi-speaker system that emits prerecorded distress calls of geese that runs on a loop every 10 minutes. Here are some do-it-yourself ideas:

  • Stop feeding the birds. It might seem obvious, but when you throw bread to seagulls or other birds near your boat, they'll keep coming back.
  • A plastic owl works great for some, but problems include the owl blowing away or the birds getting used to it and coming back. One reader wrote that hanging an owl from the spreader, so it moved slightly, made it more effective.
  • Cormorants tend to like being high up (sorry, sailboaters), so one reader found that covering the top of the mast with tacks stuck through sail repair tape did the trick. (Before you email saying that's cruel, our reader pointed out it was no different from a thorny branch.)
  • Stringing monofilament line on favorite perches on the boat has worked well for many. Just don't tangle yourself up in it or let it fall overboard. Recycle if you can, and otherwise dispose of it in a covered receptacle.
  • Pinwheels, multicolored flags, and shiny string or ribbon festooned around the boat is was another good tip.
  • Large wind-driven "rotators" work well, as do bird "spiders." They're easy to put on the hard top, bow, or back deck, and easy to take off and stow when it's time to use the boat.
  • A large feather duster (preferably ostrich) stuck in a box on the deck allegedly worked for one reader.
  • Got trouble with birds of the webbed feet variety? Hot sauce diluted in water on the final washdown where your unwanted guests like to walk is said to keep them off the boat. No word on whether it'll repel the visitors you want onboard, too.

My Life Changing Experience with a Baby Sea Lion

Rodents: That Which We Shall Not Mention

If you're unlucky enough to encounter rats and mice aboard the small space of your boat, you'll need to outwit the wiliest of creatures with a plan. Apart from being hugely unpleasant, they can become costly — chewing plastic fittings and wiring, which has been known to sink boats.

Hole in boat hose

This owner was lucky. A muskrat chewed through a section of hose that was above the boat's waterline.

Here are some do-it-yourself ideas:

  • Prevention is better than cure. Store food in glass jars, and regularly dispose of garbage.
  • Cover vents, if possible, when you're not using the boat. Put wire mesh or hardware cloth on the inside if the vent needs to stay open.
  • Rats are nocturnal and like it quiet and dark, so leave a bright light on and maybe the radio, if you can.
  • Get a dog. Enough said.
  • There are ultrasonic mice- and rat-repellent devices available that don't use much battery power. You won't be able to hear them, but they might drive your dog crazy.
  • If there's already a rat aboard, you'll need to consider traps. Peanut butter and avocado are favorite foods. As soon as you catch one, get rid of the trap. Same goes for mice. You can wash it, but if the trap has the smell of death, only the most desperate rodent will eat from it.
  • Some boat owners swear by ammonia. Rats hate it. Soak a towel and leave it out in the open (but out of the weather) on something plastic so it doesn't discolor the boat. (Never mix ammonia with bleach.)
  • Off season when your boat is stored or not in use, check it regularly. If you discover that you have mice aboard or (horrors!) a rat, you can deal with it early before it eats through your wiring, or worse. (Look for droppings or damage.)
  • Docklines and fenders are bridges for rodents, so position your boat in the middle of the slip if possible, and keep lines taut to prevent the boat from drifting close to the dock. If there's a known rodent problem in the area, try pie-pan deterrents. Put a clean hole in a metal pie pan and put one on each dockline to obstruct the creatures from boarding.

Sea Lions: Hear Them Roar

This tends to be a West Coast problem, but these 300-pound uninvited guests can climb aboard. There's not much to recommend sea lions as visitors, and they're protected from hunting, killing, capture, and harassment by the Marine Mammal Protection Act. Apart from the mess they leave behind and the noise they make, if your boat becomes party central for a bunch of sea lions, they can sink it. "These guys, if they're on your boat, you've got a lot of scrubbing to do," says Chris Miller, harbor resources manager at Newport Beach, California.

Sea lion on boat

Photo: Beth A. Leonard

"I've seen them push the door from the swim platform into the cockpit where a lot of people have cushions and canvases, so you get drippings and droppings there, and it can start to smell bad. But the biggest complaint is the barking," says Miller. "At night it's very disturbing." Add to that the fact they live in fish, eat fish, and smell like fish.

Like everything else, prevention is easier than cure. Those on mooring balls who leave their boats for extended periods are particularly susceptible. Here are other do-it-yourself ideas:

  • Sea lions typically like anything to which they can gain easy access. Catamarans and boats with lower gunwales are favorites, and boats used less frequently become hot spots. Plastic chairs, barrels, and crates on swim platforms or steps seem to work as a deterrent.
  • Bow-to-stern canvases that wrap the boat are another way of keeping them off but are a hassle to undo every time you want to use the boat.

Dealing With Creepy-Crawlies

The first year my wife, Rita, and I kept our boat in a covered shed, we were in for a surprise. We loved that the roof over the boat kept the rain, sun, and snow off the boat, but we didn't love the little black dots that kept appearing on the fiberglass surfaces that looked like tiny tar spots. We soon found out that these were spider droppings. They were the very devil to remove from the boat. We tried all sorts of potions and home remedies; none were effective. The best defense, we found, was to keep the boat well-polished and waxed, which made the mess far easier to clean up. Here are some tips to deter them as well as other common pests.

Ants. You may not notice ants at first, but they can set up large nests, often in an out-of-the-way dark corner. For a natural deterrent, some cloves placed in strategic locations seem to help deter ants from multiplying.

To kill an ant colony aboard, mix borax and powdered sugar. The ants will carry the mixture back to their colony, killing other ants there, too. After allowing the mixture to perform the grizzly deed for a week or two, all the ants and eggs should be dead. And aside from finding dead ant bodies everywhere, they're relatively easy to vacuum up.

Cockroaches. Of all the pests that you can have aboard, nothing is more likely to send the crew screaming for the hills than cockroaches. These bugs scavenge for food aboard the boat, and I've found them in the most unlikely of places — pockets of foul weather gear!

When we were sailing around the world, we were cautious about doing everything we could to keep cockroaches off the boat. We brought no cardboard aboard as, apparently, roaches are very fond of the cellulose in cardboard. We placed bay leaves in many places, and this seemed to prevent the problem As for commercial solutions, buy some roach bait stations or Roach Motels to catch/kill any that are already aboard. If things get really out of hand, the only remedy is to fumigate the boat with special smoke bombs, leave it closed up for two days, and stay elsewhere until the deed is done.

Spiders. To prevent spiders from setting up home aboard, many boaters use peppermint oil or pieces of peppermint soap, both of which seem to be universally endorsed for deterring spiders while also making the boat smell nice. While peppermint is an excellent choice for the boat's interior, we had less success on the exterior. Some people swear by spraying the mooring lines and handrails with Star brite Spider Away (available from and, which helps keep the boat spider-free for up to two months.

Most people who have a spider problem clean the little black poop dots off the boat using either a spray-on oven cleaner or Scrubbing Bubbles toilet cleaner. For particularly tricky stains, a Magic Eraser works well, although it dulls the boat's surface and removes any wax, which will need to be reapplied.

— Mark Corke

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Ann Dermody

Contributor, BoatUS Magazine

Ann Dermody is the former managing editor of BoatUS Magazine.