By Don Launer
Article taken from Good Old Boat magazine: Volume 4, Number 5, September/October 2001.
Solving the problem of icing up in winter
For those of us who live in the higher latitudes, the approach of the fall season reminds
us of an upcoming conflict between our boating agendas and the impending
deep freeze. For a fortunate few, this means stowing those summer clothes
on board and sailing toward warmer climates. But most of us will make
arrangements at the local marina for a haulout and winter cover or possibly
for wet (in-the-water) storage. Those who have their homes on the banks
of navigable water and have their boats moored at their own docks or at
the community dock of a condominium have yet another option: wintering
their boat in the water at her normal location near home. This option
requires appropriate preparation and equipment, of course.
One of the problems with wet storage in latitudes where the surface of the water can freeze
solid during the winter is the potential problem of ice damage, unless
proper precautions are taken.
With wooden hulls, water getting between the planks can freeze, spreading them apart and
allowing more water to enter and re-freeze until a major leak (and possible
The problems are usually less threatening with fiberglass boats. However, when thick ice forms
around the hull of any boat, damage to the rudder and prop is possible.
Also, when a boat is surrounded by ice, wind and current will cause it
to rock and pitch. The resultant grinding action of ice against the hull
can cut away at the gelcoat along the waterline of a fiberglass boat.
This can result in water incursion into the laminate and, at the very
least, an additional gelcoat repair job in the spring. With wood boats,
ice can wear through the paint and gouge the hull. Depending on the waterline
hull shape, major structural damage is possible. For all of these reasons
it’s important to prevent ice from forming around a boat that spends
the winter in the water.
To make sure the boat is floating in above-freezing water, a water de-icing system in the
winter is the answer. These systems are just as practical for an individual
boat at a private dock as they are for a large marina. For those who live
where the waters freeze during the winter, the “bubbler”
and underwater agitation-motors are a familiar sight, but how do they
keep the water from freezing around our boats?
Properties of water
The designer of our world certainly gave us a great gift when the physical
properties of water were promulgated. Water, one of the most commonplace
and familiar of all natural substances, is one of the most remarkable.
Compared with nearly every other substance, water behaves, physically,
in a unique manner.
Nearly every other material expands when heated and contracts when cooled, but water follows
this pattern only in part. As it is cooled down to about 39° F it does
indeed contract; but with further cooling it begins to expand again, and
when it begins to freeze this expansion is dramatic.
Let’s imagine what would happen if water did not follow this aberrant behavior. If water
and ice continued to contract, as does nearly every other substance, ice
would be denser and heavier than water. As ice formed at the cold interface
of water and air, it would sink to the bottom.
Other layers of ice would also sink as they formed, until the entire body of water would be
frozen solid. Since sunlight and heat don’t penetrate very deeply
into a body of water or ice, none of our lakes, streams and bays in the
northern latitudes would ever thaw out in the summertime, except to a
slight depth at the surface. Fish and nearly all forms of aquatic and
bottom-life could not survive, and our northern bays, lakes, and streams
would be useless as a food source, for recreation, or navigation.
When a body of fresh water is cooled, it gradually contracts and becomes
denser and heavier until it reaches 39° F. Then it begins to expand as
it’s cooled to the freezing point and is transformed into ice at
32° F or less. Although the temperatures given in these explanations are
for fresh water, salt water follows a similar pattern. In the case of
salt water, the exact temperatures at which these events happen are determined
by the water’s salinity.
A solution of salt
and water freezes at a lower temperature than fresh water. In fact, the
freezing point of a saturated solution of salt water is about 6° C,
whereas the freezing point of unsaturated ocean water (depending on salinity)
is around 21° F.
Since surface water cooled to 39° F becomes denser, it sinks to the bottom. It is then replaced
by warmer bottom water, which then follows the same scenario. Thus no
ice can ever be formed on the surface of a body of fresh water until the
whole body of water is cooled to 39° F.
This means that the water at the bottom of a deep-frozen lake is near 39° F whatever the temperature
of the air above the ice. De-icing systems take advantage of this physical
fact of nature, using this huge reservoir of “warm” water
at the bottom for their supply of de-icing water.
Bringing water up
The two popular methods of raising this bottom layer of water to the surface are the air-bubbler system and the propeller-agitator.
With the air-bubbler, a weighted, perforated hose is laid along the bottom and connected to
an air compressor (controlled by an air thermostat). The rising air bubbles
coming out of the hose carry along with them the above-freezing water
from the bottom, creating an area of unfrozen water above the bubbler
The propeller-agitator accomplishes the same result by using a hermetically sealed electric motor
with a propeller attached. These agitator units are also controlled by
air thermostats. Naturally, the deeper the water at the slip, the larger
the reservoir of warmer water and the more practical the de-icing system.
A bubbler system can be used equally well for an individual boat or a huge marina with
the physical size of the compressor and its horsepower dependent on the
length of the bubbler hose and depth of the water. Originally these compressors
were quite noisy and could be annoying in a residential environment. In
recent years, however, internal as well as external sound-proofing and
state-of-the-art compressor design has nearly eliminated this problem.
During the winter, compressors usually live at dockside and must be in
a location well above any possible flooding.
The underwater agitation motor is completely quiet, except for the rippling noise of the water.
If depth is sufficient, the underwater motor can be hung directly beneath
the boat. Alternately, it can be hung at an angle off the side of the
boat where the water is deepest, or at the bow facing aft. These motors
can be suspended by their own ropes, mounted to a rigid arm, or suspended
from a flotation unit. Most manufacturers of agitator motors have optional
dock or piling mounts and flotation-mounting kits. When the underwater
motors are mounted in the vertical position, these units produce a circular
pattern of unfrozen water. When suspended at an angle, the pattern is
Adjusting the angle of a rope-suspended motor is done by simply looping one of the suspension
ropes back one or two ribs on the propeller cage or through one of the
off-center holes in the housing placed there for that purpose. These underwater
motors have plastic propellers and replaceable zinc anodes for electrolysis
reduction and are available in 1/2-, 3/4-, and 1-hp sizes, depending on
the size of the area to be de-iced and the severity of the winters. Originally,
the motor cases were filled with oil, but recently synthetic dielectric
lubricating fluids that are non-toxic, biodegradable, and non-bioaccumulating
have been introduced.
Bags and debris
Although it would be nice if our waters were pristine, unfortunately underwater
plastic bags and other debris are a fact of life. If a de-icing system
is used in an area where large amounts of such things are present, the
chance of their fouling the propeller of an underwater motor must be taken
into account when selecting a de-icing system. Naturally, underwater debris
presents no problem to a bubbler system.
If you’re using a propeller-agitation system, the following practices are recommended:
- It is usually easier to de-ice a boat by installing the de-icer at the bow and pushing
the water toward the stern, since boats are designed for easiest water-flow
in that direction.
- If a boat is berthed in a river, de-icing from the upstream side will allow the current to
help, rather than hinder.
- When a boat is wintering next to a bulkhead, the motor can be hung off the free side
and canted toward the hull.
Obviously neither type of de-icing system can possibly prevent ice around a boat if the
ice is being moved by wind or current.
De-icing systems are also very effective in preventing damage to pilings
and docks in tidewater locations. In these locations, when ice freezes
solid around a piling, the piling is frequently lifted inch by inch at
each tide change. This results in expensive dock and piling repairs or
replacements, come spring. Unfrozen water around the pilings can prevent
this costly problem, and marinas often use bubbler systems in their slips
whether or not any boats are present. This lifting or “jacking”
damage is also common in the lakes, where weather, wind, and changes in
lake levels can cause the same thing to happen.
Although we only think of water agitation systems for boating use, they are also used as aeration
units in fish farms. A spectacular and bizarre use of a motor/agitator
made world news when, in October 1988, whales trapped by ice at Barrow,
Alaska, were kept in an ice-free area until Russian and U.S. icebreakers
could open a path for them to open water.
Even though de-icing systems eliminate most of the problems associated with wintering in the
water, some other things to consider are the possibility of freezing problems
inside the hull. The relatively warm bottom water surrounding the hull
typically will keep the bilge free of ice, but in harsh northern climates
there’s no guarantee. Where electricity is available, many boatowners
use electric light bulbs or small heating elements inside the engine compartment
to help keep the packing glands around the prop shaft and rudder shaft,
as well as the cockpit drains, from freezing. Small, inexpensive, plug-in
thermostats are also available so the heat is not on during warm spells.
People who use a light bulb for heat can encounter several problems. A
normal light bulb has a life expectancy of about 750 hours. This means
that if left on continuously, it will last about a month – not
nearly long enough to last through the winter. A long-life bulb, which
puts out the same amount of heat, but less light, has a more rugged filament
and less chance of burning out over the winter. It’s also much
less vulnerable to vibrations. An outdoor bulb should be used if there
is any possibility of water dripping on it. The problem with light bulbs,
in general, is that the very limited amount of heat generated is only
effective within a very confined space and where winter temperatures are
There have also been cases where an exposed bulb has come in contact with flammable material
or has shattered and caused a fire. Marine-grade engine-compartment heaters
are a far better and safer way to go. These come in several styles and
wattages. Some of these heaters have their own built-in thermostats and
circulating fans and are in stainless-steel or aluminum cases.
Other items to check before in-the-water winter storage, are the condition of your automatic
bilge pump and supply of power. Is the float-switch free of debris? Can
the pump be left in a standby mode without leaving the main 12-volt battery
switch on for the rest of the boat? Is there a possibility of the bilge
freezing, rendering the float-switch inoperable? Can the batteries remain
in a charged – but not overcharged – state by use of a “smart”
battery-charger or trickle-charger? Have you added non-toxic anti-freeze
to the bilge and pumped it through the bilge-pump and discharge hoses?
Other than the cockpit drains, are the through-hull seacocks closed? Ice
can lift off a hose. While you’re at it, now is a good time to
see if those hoses are double-clamped and the clamps and hoses are in
Even though you have done all the winterization tasks properly, an occasional mid-winter visit
inside the cabin is always a good idea to make sure everything is OK –
if only to assure your boat and yourself that there are warm breezes and
sunny days to come. After your checkout, a half hour curled up on the
settee with your hands wrapped around a hot cup of coffee as you plan
those summer cruises can be great therapy in relieving the depression
of those cold gray days of winter as you wait for spring to creep north
to reclaim the shoreline.
Resources: Manufacturers of propeller-agitation units:
Kasco Marine, Inc.
800 Deere Road
Prescott, WI 54021
Follansbee Dock Systems
Follansbee, WV 26037
Manufacturer of bubbler de-icing systems:
World Wide Enterprises
19 Cedar St.
East Falmouth, MA 02536
Pyramid Technologies LLC
45 Gracey Ave.
Meriden, CT 06451
The Power House, Inc.
20 Gwynns Mills Court
Owings Mills, MD 21117
Manufacturer of engine compartment heaters:
3301 Myrtle St.
Edisto Beach, SC 29438
Don lives on a
waterway off Barnegat Bay, on the New Jersey coast. He keeps his schooner,
Delphinus, at dockside next to his home. Although Barnegat Bay and the
adjacent waterways frequently freeze solid, his boat has wintered in unfrozen
water for the past 21 years, protected by a water-agitation system and
an electric engine-compartment heater.