Why narrowboats suffer more than houses

Living aboard through a British winter is one of the loveliest things you can do — frost on the towpath, a mug of tea in hand, the stove ticking over. It's also when condensation quietly gets to work. A narrowboat is a steel box sitting in cold water, with a relatively small internal volume and a lot of people, cooking, breathing and showering inside it. Warm moist air meets cold steel, and water appears. Every litre of moisture you produce has to go somewhere, and if it can't escape, it lands on your windows, hull sides, mattress bases and locker lids.

The results aren't just unpleasant. Persistent damp causes black mould on linings, rusts the steel behind them, rots timber battens, and sours bedding and upholstery. The good news is that condensation is almost entirely manageable with a handful of sensible habits and a few modest bits of kit. It's rarely one big fix — more a case of stacking up small ones until the boat stays dry.

Ventilation is the fix that feels wrong

The instinct in cold weather is to seal the boat up tight and keep the heat in. That's exactly the wrong move. Moist air needs somewhere to go, and if you don't give it an exit it will find the coldest surface in the boat and condense there instead.

• Keep your mushroom vents open, even in a hard frost. They're deliberately designed to allow a slow trickle of air through the cabin. Blocking them to stay warm trades a small draught for a large damp problem.
• Leave a hopper window or side hatch cracked on the sheltered side when you're aboard and cooking or showering. Even 10mm makes a measurable difference.
• Don't block low-level vents, including any under the gunwales or in the front doors. Cross-flow matters: air in low, air out high.
• Run your extractor fan in the galley and the bathroom for a good ten minutes after use, not thirty seconds. If you haven't got one, a small 12V fan mounted in a hatch is a worthwhile winter project.
• Air the boat properly once a day. Throw the front doors and rear hatch open for a few minutes, even when it's freezing, and let the whole volume of air change. It cools the boat briefly but dries it dramatically.

You'll burn slightly more fuel keeping a ventilated boat warm, but it's far cheaper than replacing rotted lining and mouldy mattresses.

Sort the insulation and the cold bridges

Condensation forms where warm moist air meets a surface below the dew point. On a boat, those surfaces are usually window frames, the steel behind thin linings, and any metal that bridges from the outside hull to the inside cabin. Spray foam or rigid board behind your cabin linings does the heavy lifting, but even a well-insulated boat has weak spots worth attention.

• Line your windows at night. Thermal blinds or a second layer of cheap bubble wrap held against the glass with tape makes a startling difference and stops water running down onto the woodwork.
• Insulate cold pipes and any exposed steel around the bow, stern and lockers. A length of pipe lagging costs pennies.
• Lift mattresses and cushions off solid bases with slatted frames or a mesh underlay so air can circulate underneath. This is where mould loves to start.
• Check your pram hood or cratch cover — if it leaks or traps damp against the front doors, it's feeding moisture straight into the boat.

Cut the moisture you're making in the first place

Ventilation and insulation deal with the moisture already in the air. Reducing what you produce makes life much easier.

• Always use pan lids when cooking and keep the extractor running. Boiling pasta for twenty minutes with no lid puts a surprising amount of water into the cabin.
• Shower with the window or hatch open and squeegee the walls afterwards. A shower box that stays wet all day keeps feeding the air.
• Dry washing ashore or in a launderette wherever possible. Drying clothes inside a boat is the single biggest condensation culprit in winter — if you must, do it near an open hatch with a fan moving air across it.
• Wipe down windows and frames daily. A quick pass with a microfibre cloth and a squeeze into the sink stops water running into timber and rusting frames.
• Empty your bilge and keep it dry. A damp bilge under the floor quietly humidifies the whole boat. A bilge pump and a sponge are your friends.

Moisture traps, dehumidifiers and traditional tricks

Absorbers aren't a substitute for ventilation, but they help in cupboards, lockers and under bunks where air doesn't move. Crystal moisture traps, often sold for caravans, are cheap and effective — check them weekly and refill or replace as needed. Charcoal bags do a decent job of keeping wardrobes and bedding lockers fresh, and can be dried out in a low oven and reused.

For a small 12V or mains dehumidifier, look for one with a decent extraction rate and a drain option so you're not emptying a tiny tank twice a day. Running one for a couple of hours in the evening, with the boat closed up, pulls a surprising amount of water out of the air. Just remember to air the boat again afterwards. Never seal up a boat with a dehumidifier running and expect the damp to simply vanish — the moisture has to leave the boat or end up in the tank.

Daily habits that keep a boat dry

Condensation is a routine problem, so routine is the cure. Make a short daily loop part of life aboard: open the vents and a hatch in the morning, wipe the windows, empty the moisture traps, run the extractor while you cook, shower with the hatch open, and give the boat a proper airing before bed. Once a week, lift the mattress, check under the bunk, look behind the curtains and inspect the bilge.

Do that and you'll spend the winter warm, dry and mould-free — which, after all, is the whole point of living on the water.