The Comfortable Cruiser

By Bob Wood

Article taken from Good Old Boat magazine: Volume 3, Number 1, January/February 2000.

Controlling your environment makes you a better, safer sailor

Dressed for foul weather, dreams of easy sailing

As a person to whom quality time and time aboard are synonymous, I often
daydream of idyllic passages through tropical seas with steady trade winds,
puffy white clouds, and sun-sparkled wave tips at my back. Moments later,
reality returns to find me clutching a warm coffee mug and watching my
steaming breath join the rest of the condensation coating a frigid cabin.
Or it finds me pondering, with burning eyes, the flies gathered on the
mainsail during a windless, steamy August afternoon.

We need to cope with an amazing range of temperatures and conditions over
the course of a typical boating season. Moreover, we do it in a comparatively
Spartan way, without a basement full of extra equipment. We do our best
to cope with this temperature range for two basic reasons: comfort and
safety. A sailor preoccupied with discomfort is going to be at a disadvantage
when decision-making time suddenly arrives.

Basically, we must address two environmental issues while boating; how
to stay warm when it’s cold, and how to cool off when it’s hot. Let’s
look at the mechanics involved and then take them in turn.

Heating and cooling are two sides of the same coin: the physics of heat
transfer. When heat is transferred from place A to place B, A will get
cooler while B gets warmer. There are three ways that heat is moved around:

  • By conduction, when your hand touches a hot stove, directly transferring
    the stove’s heat.
  • By convection, when fan-blown air delivers heat from the stove.
  • By radiation, when the hot stove’s surface or its flames emit infrared
    waves that warm the objects that absorb them.

Those are warming situations; but keep in mind that if you were the stove,
they would be cooling situations . . . different sides of the same process.
To stay comfortable, our human efforts are directed at either enhancing
or reducing the transfer of heat.

Staying warm

Types of heaters

There are several ways to combat cold. Each of the following five basic
types of marine heat generation has advantages and disadvantages.

Electric heat is quick, inexpensive to install, very easy to start
and adjust, requires no exhaust venting, and doesn’t add moisture to a
boat’s already moisture-laden atmosphere. It is also impossible to use
away from the dock without running a generator. Electric heat must be
carefully designed to prevent shocks and fires. And, finally, not all
marinas provide sufficient power to run these heaters. There are electric
furnaces with blowers and air ducting to efficiently heat the long skinny
interiors of boats, but many medium-sized boats can do quite well with
a portable, fan-assisted electric heater. If your home port is north of
the Mason-Dixon Line, dockside electric heat represents a good investment
for chilly mornings and evenings, often extending a season by two or three
months. When buying a portable heater, make sure that it has:

  • a three-pronged safety plug;
  • a thermostat that shuts it off at the desired temperature;
  • a tip-over sensor (if it’s portable) that shuts it off should a wake or other sudden motion knock it over; and
  • a ground-fault interrupter (GFI) or receptacle. In fact, all alternating current-powered appliances aboard should have, or be plugged into, a GFI.

Those precautions, along with sensible and prudent operation, will make
electric heat an enjoyable convenience.

Solid-fuel heaters have the advantage of burning a wide variety
of readily available fuels such as charcoal and wood. They produce a quiet,
dry heat and sometimes a nice ambiance if the fire is visible. The price
is also moderate, and they can be used under way or while you’re swinging
on the hook. On the downside, they do require venting, and their smoke
can foul sails or topsides. They take the longest of all heaters to begin
producing heat, and a bag of charcoal is not the cleanest item to be rattling
around in a locker. Finally, burning ocean driftwood can create mildly
corrosive smoke that hastens your heater’s demise. Still, solid-fuel heaters,
with their warmly glowing flames, rank second of all heating types with

Propane, butane, and compressed natural gas (CNG) are gas fuels
with some commonalities. They are quick to produce heat and difficult
to fine-tune; they will work at the dock or under way; and they are clean-burning.

Most require venting, and I would advise against those that don’t on two

First, some of the catalytic types that don’t require venting are designed
for a semi-open space with plenty of fresh air moving through . . . and
moving the waste products out as well.

Second, the combustion process for gas fuels produces a lot of water vapor
that will be deposited in the dark cold corners of your boat unless it
is vented outside with the other fumes.

There can also be a definite fire hazard when you use a portable catalytic
heater in your boat, especially while under way. I would caution against
doing it. Period.

CNG is lighter than air and will, therefore, not settle in the bilges
like propane could. CNG is also much harder to find than propane wherever
you sail. Propane is quite safe when it’s installed with properly isolated
storage bottles, a correct solenoid shut-off valve, systematic maintenance
of the lines, and a good gas-detection alarm. If you already have propane
for your galley, it may make sense to use it for heating, also. Permanent
marine propane heaters are more expensive than solid-fuel ones, but less
expensive than liquid-fuel heaters.

Liquid-fuel heaters are primarily kerosene- and diesel-fuel heaters.
They are the benchmark by which traditionalists rate all others. They
provide a steady source of low-cost heat while under way, on the hard,
and all points between. If you already have a diesel-fuel galley stove,
you probably don’t need a heater, since the stoves I’ve been around warm
a cabin very well.

The heaters require venting, and the smoke can stain sails over a period
of time. They are also among the most expensive of the different types
of heaters. Since they require gravity-fed or pressurized fuel, a special
tank is sometimes the easiest way to install the system.

Lastly, your cabin can get smoky if fluky winds swirl fumes from the stack
back around the mandatory open hatch or port. A diesel-fuel heater is
for hard-core sailors who rejoice in the glitter of frozen halyards. Serious

Alcohol heaters are portable and inexpensive, but not in the same league
as kerosene/diesel types. Their flame is difficult to see, increasing
the possibility of burns, and they pump lots of undesirable water vapor
into the cabin air. It’s hard to recommend them for boating purposes.

Hot-water radiators. This last heat source is probably the least
used. Radiators produce heat from the water used to cool your inboard
engine. These are not often seen on sailboats, despite the fact that many
a voyage transforms our wind yacht to a displacement-powerboat-with-mast.

Radiators work only when the engine is running, which allows powerboats
to make good use of the free, quiet heat. They produce a dry heat with
no venting required, no fire danger, or smell. They begin providing heat
within minutes of the engine’s being started, and are easy to adjust.
Most installations are custom-made and, therefore, can be expensive. The
radiator preferably uses the heat-exchanger fluid since it’s hotter, but
raw cooling water can be used – although a broken hose or fitting could
flood the cabin.

Humidity’s effect

Humidity, or water moisture in the air that you’re heating, makes a difference.
The more water moisture, the more heat that air can hold. Dry air requires
a higher temperature to be comfortable. Since most heat sources do not
add water vapor, the air becomes drier as it gets warmer. Unless you have
the perfect boat with bone-dry bilges, chain stowage, lockers, and bedding,
you probably won’t have to worry about over-dry air while bobbing on the
waves. The exception would be heating while hauled out during sub-freezing
winter weather; then a pan of water boiling on the stove might help.

Circulation – air layering

The numbers game

are formulas for converting watts to Btu (British thermal units),
determining resistance to heat loss (insulation factor), and number
of tons of air conditioning needed. But forget the numbers; boating’s
wide array of types and conditions make them impractical. Your electric
heat will be limited to what your marina can provide: typically
enough to run a 1,600-watt heater at 110 volts.

With care, this will keep a saloon and one stateroom comfortable
down to around freezing . . . remembering that comfort is a relative
term. Any requirement greater than that in size or temperature is
going to require a fuel heater. Heaters made for permanent marine
installation will advertise figures in Btu output, but basically
they’ll be good for boats up to about 45 feet and temperatures down
to 300F. Dealers in marine air conditioners will help you figure
your cooling requirements based on climate, boat insulation, and
installation location.

A boat has a lot of nooks and crannies, is poorly insulated (compared
to a house), and usually has a single point of heat. If a fan isn’t used
to push the air around, the nooks and crannies and outer surfaces stay
clammy while the air immediately above the heat source becomes uncomfortably

Unless those on board can levitate to the 720F air layer, everyone is
going to be miserable – cold and clammy from the knees down, and feverish
from the shoulders up. A fan is essential for heating comfort. Small,
low-wattage fans can be mounted in passageways forward and aft to immensely
improve the main fan’s function. Layering is good for clothes, bad for
cabin air.


An airtight heated cabin is an invitation to disaster. At the very least,
you’re inviting headaches, as the oxygen content is depleted by fuel-burning
heaters. Carbon dioxide and carbon monoxide levels increase, aggravating
the stale conditions. Moisture from respiration and perspiration has no
place to go to, except onto exposed surfaces. It will cake your sugar
and salt into unusable blocks. You need to have a hatch, porthole, or
Dorade vent partly open, even if it’s below freezing and snowing sideways.


The opposite of an airtight cabin are drafts so bad that a candle or lantern
can’t stay lit. This is unworkable, because all the air that you’re heating
is leaving. It’s going to take a lot of fuel to raise the temperature
if you’re heating the entire Western Hemisphere. You don’t need all downwind
hatches open . . . maybe just one, or a half of one.


Don’t overlook the value of dressing for temperature rather than changing
the temperature for your dress. It’s quite possible to be comfortable
at 550F or cooler temperatures with warm boots, hats, and gloves. You
lose the most heat from not wearing headgear . . . a warm hat and scarf
are probably worth 50F of cabin temperature by themselves. You’ve heard
it before, but dress in layers: a layer closest to the skin that will
wick moisture away, then a bulky insulating layer or layers to hold body
heat in, finally an outer layer that’s wind-resistant, to reduce loss
of heat by convection or drafts. If you typically sail in colder weather,
have boots large enough for two pairs of socks and make the outer layer
a pair of good-quality wool . . . wool retains heat even when it’s wet.

Keeping cool(er)

For many sailors, comfort means any way to stay cool on hot days. For
some, staying cool is synonymous with air conditioning, but there are
other approaches.

Air conditioning

Marine air conditioning is much like marine electric heat; it works well
with shore power, with gen-set power, or with an extremely long extension
cord. For powerboaters, there are air conditioners that work from a power
take-off on the engine. Like radiator heating systems, the engine has
to be running for power take-off systems to operate. Air conditioning
accomplishes at least four things: it cools the air, creates air movement,
removes excess moisture, and filters some airborne particles.

It also requires a well-sealed cabin to be effective, and a compressor
location with plenty of fresh-air circulation to take away the heat. Systems
can be on the pricey side, but if you’re lying alongside the dock at West
Palm Beach for an extended stay in July, life as we know it suffers without


Air circulation helps in reducing the effects of uncomfortable heat. It
promotes the evaporation of perspiration, which lowers our body temperature
and makes us smile. If your boat is swinging on the hook, or otherwise
moored on a windless day, circulation is spelled f-a-n-s.

For a very few dollars (less than $10) mail-order suppliers such as Northern
Hydraulics or Harbor Freight often sell small, surplus, 12-volt box fans
that draw less current than a light bulb. You may even find some that
have hinges, so they fold against a bulkhead when not in use. Having two
of them in the main saloon and one in each stateroom is not overkill,
andyour batteries won’t go dead in a day, either.

For best results, aim them directly where people will sit (or lie) at
about chest level. They make a big difference and also help during the
frosty season for distributing your heater’s munificence. If you run your
engine about an hour a day, your batteries will never suffer any undue

Under way or on any windy day, circulation is spelled h-a-t-c-h-e-s. The
more, the merrier. The bigger, the better. Opening ports are nice but
usually too small, and their insect screening further reduces the airflow.

Ideally, on a good old boat of about 35 feet, there should be two hatches
in the cabin overhead, one above the galley and one above the seating
area. There should also be an overhead hatch in each stateroom. All of
this is in addition to opening ports.

Incidentally, I don’t like forward-opening hatches in the V-berth area
or anywhere else. Boarding seas will quite likely carry them away if they
catch them undogged. Trawlers, whose foredecks are much higher, fare much
better with forward-opening hatches.


Hand-in-hand with circulation goes ventilation. On hot sultry days, you
need fresh air below, unless you’re running the air conditioner. Seasickness
is not eliminated by fresh air but it sometimes helps. And fresh air always
helps those who are aboard with the seasick victim. Fresh air also means
keeping engine room air separate from cabin air. Even in a spotless engine
room without exhaust leaks, engines get hot and fill the air with lubricating-oil
fumes and bilge fumes. They need lots of fresh air and ventilation, but
not via the cabin.

There is one particular no-win situation: running downwind under power.
It’s much better to bear off a few degrees than to suffer the exhaust
fumes in the cockpit and cabin, no matter how good your ventilation is.


Our natural cooling systems depend on the evaporation of perspiration
(sweat) to reduce body temperature. The moisture for sweat is carried
by the vascular system. If you don’t drink sufficient water, your blood
doesn’t have as much to give the skin, and you’re going to feel warmer.

Drinking lots of liquids on hot days helps our cooling systems. Taking
salt tablets helps the body increase the vascular volume, thus more liquid
is available for the skin. For those of us on the far side of 39, perspiration
is generally reduced. We therefore really appreciate any additional cooling


Increased humidity slows our rate of perspiration evaporation, and thus
our cooling off. You will feel more uncomfortable at 900F and 90 percent
relative humidity (RH) than at 900F and 50 percent RH. Aside from cranking
up the air conditioning or heading for the clubhouse, combating high humidity
requires shade, air movement, and loose-fitting clothing.


The value of shade is often underestimated when you’re trying to cool
your boat. A Bimini top is wonderful for the cockpit if the sun is directly
overhead. Short side-panels dropping down from the Bimini about a foot
will increase its shade area by at least 50 percent and won’t noticeably
reduce the ventilation, especially if the panels are made from weighted
screening. Lastly, consider a Bimini extension over the cabin roof. Shading
this area will definitely make the cabin cooler and help the air conditioner.

Bob Wood

Bob Wood learned to sail on small O’Days more than 30 years ago. He has owned an odd assortment of sailboats and sailed them in waters from the Florida Keys to British Columbia’s Gulf Islands and from New York’s Finger Lakes to Colorado’s and Idaho’s impoundments and reservoirs.

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