How to keep cool when sailing in the tropics

Ask people where they would like to cruise and only a few will name Antarctica or other places that require no refrigeration onboard.

Most will want to go somewhere “warm and sunny”. Throw in a few palm trees, warm water and we have the tropics; very many popular destinations abound between 20 degrees south and 20 degrees north which has long been known by many as the only region of our planet capable of supporting
cruising life.

While this may not be strictly true there are enough cruising boats within the area to make a debate of the issue.

Never getting cold however has a cost and this cost is getting hot. Tropical weather forecasting (temperature anyway) is easy, as Robin Williams said in Good Morning Vietnam all those years ago, “it’s going to be hot, damn hot”.

Well nothing has changed since then and cruisers have been finding ways to stay cool since day one; here are a few of the more popular ideas.

Shade is our friend

Mad dogs and Englishmen may stay out in the midday sun but it is obvious that shade is required if we want to have any chance at a civilised temperature.

You can test this theory personally in about five minutes; stand in the shade for 2.5 minutes then stand in the sun for the remaining 2.5, see the difference?

So to this end some type of awning is required to shade as much of the boat as is practical. Temperature inside the boat will be significantly reduced all day and this of course means a cooler vessel at night. Even catamarans, many of which have a shaded cockpit by design, opt for a full cover when at rest.

Some designs are superbly efficient and magnificently made but so complex you need a team of circus roustabouts to put them up or down. The simpler an awning is to work with the better, as more use will be made of it and you will be cooler as a result.

At anchor awnings can be large, covering mast to backstay or beyond; many boats favour an additional, somewhat V shaped addition forward of the mast to cover the remaining deck.

This is probably not a living area as the cockpit will be the place of choice but the additional cover will keep more of the boat cool and protect from the sun.

The hatches might also be able to stay open if it rains depending on the boat and conditions. Any extra air flow is welcome, nothing like a bit of humidity in a closed up boat for your penicillin culture experiments.

Getting shade while underway is a little more complicated, vision is required so the awnings need to be smaller which of course limits the amount of shade provided.

There are thousands of variations on this theme but it appears the ‘big canvas roof’ as opposed to a traditional bimini (smaller canvas structure on a stainless frame over the helm) is becoming more popular. I can understand this as many biminis provide very little shade unless the sun is nearly overhead.

For sailing purposes the big roof is pretty much going to wipe out our view of the sails; never mind we can move to another (shaded) spot to check. Some may feature clear panels in key areas so we can peer upwards through a soon to be, (if not already) cracked, discoloured or opaque window.

What we really need here is some kind of venetian blind, pull a cord to open, leer at sail, issue commands, close blind and resume being totally shaded.

Accurate and well calibrated wind instruments, I hear you sniggering, will reduce your dependence on the masthead windex and allow a little less exposure to the yellow orb.

Good awnings do not come cheaply; marine canvas is not cheap and tailoring a good awning takes some considerable work. Work is labour and as I am sure you are aware labour in Australia is anything but cheap, assuming you can persuade someone to do it.

Given these constraints many people have opted for the tarpaulin solution. Get down to the local one dollar store, lay out the cash for China’s finest reject and string it up over the boom; ripper, got a shaded boat and cockpit.

Take the dinghy ashore for an hour and come back to what looks like a giant piece of delaminating
toilet paper clawed to shreds by a cat. Sadly the tarp was not UV stable and you did not notice the label in Mandarin stating: “suitable only for night use.”

Ventilation is free as the wind

After shade, ventilation is our best friend; get some air moving around the boat and things are decidedly more pleasant.

This moving air can be natural or induced. Hatches and portholes are good for this but will be pretty well set in concrete when you buy the boat.

I might consider replacing a fixed port skylight in the coach house roof with an opening porthole if a quality unit of the correct size (cut a larger hole, no way), were available. But very little would induce me to add an extra hatch which could have any number of ramifications.

As a matter of interest have you ever cursed a manufacturer for installing fixed port skylights instead of opening ones in the first place? Cheap swine, the only justification for this, other than price, is not having an opening over the electrical switch panel.

Most monhulls have a large opening hatch over the V berth or forward section. This, I believe, is to assist the jolly tars who do the spinnaker changes; it also makes an excellent wind tunnel.

The big lid when opened right up helps direct breeze into and through our boat. Especially good at anchor when pointing into the wind, less use in a calm marina.

Most boats will have a mixture of forward and aft opening hatches, some have sideways mounted (generally facing out board to catch waves when left open). This has the benefit of providing some chance of airflow in a marina when tied up.

Any hatch’s airflow can be augmented with a wind scoop which effectively is a big cloth funnel hung from a halyard and secured to the hatch. This increases the amount of air channeled through and is beneficial to our comfort; no help underway however when the last thing you want is a hole in your boat.

Dodgers or spray hoods as they are sometimes called are great things as most cruising sailors know, most boats have one or are getting one.

The purpose of this equipment is to block wind, spray and other unpleasantness whilst underway in exciting conditions. We definitely do not want it blocking wind when anchored in hot conditions.

Large opening windows in dodgers should be made compulsory by legislation, any canvas worker
building one without such a window and perhaps even removable sides should be banned from the trade.

So hatches and ports are fine ventilation friends when we are onboard but if the boat is left unattended they must be closed for rain and security. For passive ventilation when closed dorade and mushroom vents are perhaps the best bet.

Again most of these will come directly from the factory but you may be able to increase air flow in a dorade by increasing the size of the on deck scoop. Orient the scoop towards the prevalent wind direction if there is one for best results.

Mushroom vents might be able to be replaced with the solar powered fan version (if you have a pair as is likely, install one fan to blow in and one to suck air out) and increase the airflow. Both of these vents are waterproof (the dorades if done correctly certainly are) so you may leave them unattended.

Hot, calm and stifling, must induce wind

So passive ventilation is well and good, providing there is enough breeze and our circumstances allow us to utilise it; often they will not.

In this instance we must induce our comforting air flows. We need electric fans (unless you have a big enough boat to accommodate sufficient Punkah Wallahs) and all electric fans are not equal.

Back before every car in the world was produced with standard air conditioning there was a considerable market for 12 volt fans and possibly more companies competing for this market. That has now changed and there seem to be only a few brands producing 12 or 24 volt marine fans.

These are mind numbingly expensive for what you get. Hella and Caframo are who I am talking about.

They are also quiet, energy efficient and produce a good air flow; I just wish they would last longer. Between three or 400 dollars per year for fans is about the mark. Compared to the cost of 220 volt domestic fans it is hard to understand why a five inch marine version costs up to ten times more (in SE Asia) than a huge household number.

For the record Caframo have three basic models, Ultimate, Bora and Sirocco; these are listed cheapest to most expensive. As mentioned all are quiet, energy efficient and have good air flow and adjustability.

Bora last the longest and Sirocco (although most expensive) last the least as a result of fancy timing and other functions that require a printed circuit board which fails frequently.

Best value is probably the Ultimate as it has more wind than the Bora and costs the least. It is essential to keep these units clean to get a decent life span; vacuum the motor vents if possible and turn them off when not around to benefit from the breeze. In other words treat them like a battery powered device.

There are no oscillating marine fans I am aware of anymore, (I suspect it is because of the increased power draw), TMQ used to make one but it sounded like an air show when running and didn’t last too long.

So you will need a fan pretty much everywhere you spend a lot of time or be constantly running around changing the direction of the airflow. Galley, saloon settees, sleeping cabin, even the head can all benefit from a fan.

Regardless of the cost good fans are not an option unless you have air conditioning and the means to run it almost constantly.

The cool room

Spent all your life in frozen food factory and just can’t break that thermal underwear habit? If so you are going to need air conditioning.

This can be achieved in a number of ways with the more economical ones being (logically enough I suppose) the least convenient.

Many people carry a portable unit and simply stick it into one of the hatches when in the marina. This is fine but marina electricity can be quite expensive in some places, Phuket marinas charge many times the domestic price per unit for example.

This also requires sealing the hatch up to the unit to operate and packing the lot away somewhere when not in the marina.

If you want to use the machine at anchor you will need a generator; at the least one of the small petrol numbers. This also will require the space to store and operate and we may well end up with a deck or cockpit that looks more like Steptoe and Sons yard rather than a boat.

Trying to up anchor in a 2am squall with an air con, power leads and a generator running on the foredeck doesn’t feature in too many brochures. Locker space for these items when underway may be a challenge on many vessels.

Built in marine air conditioners are surely the best solution but bear in mind they will occupy a lot of space. The units themselves need to be mounted in an accessible area and the ducting is all run behind the scenes to the various outlets which means a very great deal of storage space is taken; the ducting is somewhat fragile also so pile items on it at your own peril.

You will also need a compatibly sized generator to run it and this means a properly installed diesel unit if you have gone to the trouble and expense to air condition properly.

In this instance the cost of never getting cold is not getting hot, it is just a matter of money.


– John Champion: John and Colleen live on their boat, Rancho Relaxo in Phuket, where John worked in marine electrics for the past few years. They bought the boat in San Diego and it has taken them a long time to sail to Thailand.


This article was first published in the January 2014 issue of Cruising Helmsman.


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