Humidity is the bane of a boaters life, it will get into your life jackets, into your foulies, into the furnishing, the untreated wood, into the curtains and anything else vaguely porous. The most efficient way to deal with tropical humidity or winter condensation involves: electric heating, fans, or air conditioning. But, mains power is not always available, especially on hard standing in a tightly packed yard. You’ll be needing other moisture sucking methods that go off-grid, and that generally involves calcium chloride salts, crystals or silica gel in the shape of several non-electric dehumidifiers dotted throughout your boat.

I’ve had lifejackets self inflate in the cupboard because of too much humidity. Zips have gone furry and refuse to move on the binocular case. My best hiking sandals were given a ceremonial send off after they too succumbed to the mildew and were ruined. And that time I opened the door to the back cabin after after a week of being closed, to be greeted with an entire new  eco system of black mold covering the side lining; well I still have flash backs to this day.  The price of not using some sort of dehumidifier can be very costly.

The best non electric dehumidifiers – tested

UniBond Mini Moisture Absorber

Specifications: dimensions: 10cm round and high. 6 weeks duration, refillable, liquid capture bowl, scented options available,

Reasons to Buy: compact unit, easy to refill, good variety of scents available

Reasons to Avoid: only works in very small spaces

These miniature moisture absorbers by Unibond,  (similar or identical units available under different manufacturer names including humdry in mainland Europe) are a great choice for small, enclosed compartments found onboard like the forepeak or galley cupboards.

While they are spill resistant, I’ve managed to spill mine on the way to the sink, so caution required if the boat is moving about a bit.

The small solid refill tablets come in two types, one with an additional scent such as apple,. citrus or lavender or plain unscented. These are a perfect companion to the other products on this group test. They do work well in small cupboards, especially galley cupboards, such as those with cans that are prone to condensation and may help to keep rusty cans at bay.

 

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Humydry Hanging moisture absorber / dehumidifier

Specifications: dimensions: 15cm wide x 30cm high, 2cm thick. 6 weeks duration, disposable, liquid capture bag, scented options available

Reasons to Buy: spill proof, easy to hang, easy to see fill rate

Reasons to Avoid: single use, can’t be refilled, hard to recycle

These hanging dehumidifiers are an absolutely essential bit of kit. So simple and yet so effective.

Put these in lockers with sailing gear, clothes, lifejackets and so on. You can hang them throughout the boat. The good thing about these is that you can easily see how much water they have collected at a glance. The fact they hang, makes them spillproof, as in, you’ll not accidentally knock one of these over and spill liquid everywhere. They just dangle away there and do their job.

These come in a variety of brand names, but they all work the same way, with salt crystals in the top section and an empty clear bag for liquid collection. Within an hour of putting these on my boat I can see the first drops of water trickling down into the bag. it’s very satisfying to see.

The only negative thing with these, they’re disposable and can’t be refilled. They work brilliantly though. I square it away by knowing that these things are saving me from far more destructive damage to expensive equipment so, it’s a tradeoff I’m ok with.

 

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Unibond Aero 360 dehumidifier

Specifications: dimensions: 14cm wide x 23cm high, 10cm deep. up to 3 months duration, refillable, liquid capture tank capacity 0.9litre

Reasons to Buy: good capacity moisture container, easy to see water level, sturdy refillable design, capsules are easy to use for refilling

Reasons to Avoid: not a sealed unit so can be spilled, the pouring bung can be a bit messy

This a popular and more stylish model of passive dehumidifier, well at least, I can say that the manufacturer has made some attempt to make it look less of a rodent trap. Though the top ventilation shape can be confusing and look like it has a built in fan or something. it doesn’t. This is entirely non electric.

I’ve used one of these for the past 10 years. I stick a new capsule in it as the dampness starts to creep in around October, it lasts usually until December, when I stick another capsule in it and then by the time that’s spent, it’s spring again and it can go back into storage. I have to make sure it is wedged in somewhere though as I have learned through bitter experience that if it can be kicked over, it will be. I find it works best on a counter top, or nestled somewhere secure but not too blocked in.

The same style unit can be found under different manufacturer names according to country territory.  Unibond is the one found in the UK. Rubson is the name of the same unit in Portugal and other parts of Europe. In the USA, it’s Damprid.
The unit is tall and slim. The Aero 360 is designed to be refilled using a hard circular puck sized tablet of Calcium Chloride. The top housing and liquid container clip together and to empty, you pull out a small pouring bung to tip the liquid away. It isn’t a sealed unit though and should be protected from being knocked over to avoid spills. Best used on a non-marking flat surface in a larger cabin or saloon.

There’s very little waste on these, the container will live for years. My current unit is over 10 years old and still going strong. The refills come in a plastic sealed pouch that is recyclable.

 

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Aero 360 refills

 

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Gel Hanging Dehumidifiers

Specifications: dimensions: 10cm wide x 15cm high, 1cm deep. up to 6 weeks duration, disposable, gel capture no spill

Reasons to Buy: unspillable gel, no water to dispose of, hanging but can also be used in drawers

Reasons to Avoid: best used in small spaces/cupboards

These are like hens teeth to find, but when I do see them, I get a small stash. The gel hanging pouches can be used in all sorts of places, not just wardrobes.
These don’t have a water collection bag as the pouch contains a variant of the usual crystals that rather than dissolve with water, they swell and become a squidgy gel.

I use one of these in my ukulele case or my mandolin if it’s onboard. it’s a non harmful, non damaging pouch that just sucks up water and keeps things from going mildewy. They’re best used in confined spaces, so smaller cupboards or awkward spaces that don’t have a flat surface are ideal spots for these.

These can also be stashed behind the electrical board/switch panel to keep moisture out of the electronics, knowing that it’s impossible to spill.

 

 

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Acana Moisture Trap

Reasons to Buy: very clean to use, no spill gel safe design, refillable

Reasons to Avoid: the gel safe pouches are difficult to recycle.

These are perhaps the best of all of the passive non-electric dehumidifiers listed above because this unit, unlike all of the others, is both reusable and spill-proof because it is ‘gel safe’. The unit uses pouches that start off feeling gritty and slowly turn to squishy gel when they’re spent.

These are optimal for both tight spots, as well as places where they are likely to be knocked over. They are non-marking and can fit into some really tight spaces. Also highly recommended for high-traffic areas.

I use these in small bathroom cubby holes.

 

 

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West Marine Air Dryer with Fan dehumidifier

Specifications: Weight 2.69lbs, Power Supply (V) 120 V, Speed Settings 1, Current Draw 70W

Reasons to Buy: circulates a good volume of dried air, very low power consumption

Reasons to Avoid: requires 120V AC (US model) or 240v (EU model)

This buyers guide focuses on methods for passive dehumidification, however this little AC unit is low powered enough that if you have a good solar array, then you may still be able to run this off-grid, so I decided to include it.  This isn’t a heater, so it’s safe to leave unattended. (check manufacturers guidelines for use) With a small footprint of approximately 25cm or 10 inches diameter it will fit easily within a cabin or saloon.

I photographed this one on a folded saloon table of a Jeanneau Sunfast 3600. It just fits within the fiddles.

 

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What we look for in the best non-electric dehumidifiers

• As these are either disposable or refillable, we’re looking for recyclable plastic or compostable materials.
• We look for units that don’t spill their contents easily, with either a deep container or a stable base
• Are refills easy to access and obtain?
• Do they actually suck moisture out of the air?
• They might have a nice fragrance to leave small spaces smelling fresh rather than stale.

 

If you want to see which electric dehumidifiers we tested, here’s our group test: Best Dehumidifiers for boats –  tested

If you are looking for more information on winterising your boat, then read more at PBO.co.uk