Atomic 4: Smooth, worth another look
By Jerry Powlas
Article taken from Good Old Boat magazine: Volume 1, Number 1, June/July 1998.
Diesel envy? Take another look at
the gasoline engine that came with your good old boat
If you own a sailboat, there
is a good chance that you recognize the Atomic 4 engine by name, even
if you don’t have one in your boat. If you have a gasoline auxiliary engine
in your boat, chances are it’s an Atomic 4. Many good old boats have them;
there were about 40,000 Atomic 4s built, and about 20,000 of them are
still pushing sailboats around. While common, these engines are also controversial.
Most respected authors who write about sailboat engines say if you don’t
have a diesel engine, you should get one. They caution that it will be
expensive to convert, but counsel that it is necessary. This point of
view is so widespread, we don’t know of any production inboard auxiliary
sailboats offered today with gasoline engines. Indeed, to our knowledge
there is no gasoline engine in production that would be a good candidate
for this application.
Marine architect Dave Gerr and Practical Sailor editor Dan Spurr are respected
authors who take the other tack. They point out that it may be difficult
to justify the cost of converting from gasoline to diesel.
If you have a reliable Atomic 4, the best advice is to keep up with the
routine maintenance and enjoy it. If you’re having problems, your options
are to repair it, get another used or rebuilt Atomic 4, or replace it
with a diesel. Four interesting factors should be considered in making
- the safety of gasoline and diesel fuels the economics of ownership the problems of maintenance
We have been told that one quarter of a
cup of gasoline evaporated into the correct amount of air will explode with the destructive force of six sticks of dynamite. It makes you think.
Before you become overwhelmed with fear and diesel envy, however, take
a walk down your dock, and ask a few diesel sailboat owners if they
have engines for their dinghies. The truth is that just about every
cruising sailboat has at least a quarter of a cup of gasoline aboard
regardless of what the main engine fuel is. All of us have to be very careful with gasoline.
Automobiles have a good, though not perfect, safety record with gasoline.
An automobile engine compartment is like an upside-down bowl. Leaking fuel and vapors fall down – out of the engine compartment and away from the car. In addition, cooling air from the radiator helps ventilate the compartment. We have never seen a production automobile engine compartment that was enclosed at the bottom. Although it might be desirable to do so to reduce drag, it simply is not worth the risk.
Marine inboard engine compartments are also shaped like a bowl, but
the container is right-side-up. The problem is caused by gasoline vapor
being heavier than air, so it tends to fall to the bottom of the bowl,
where it can be ignited by sparks or flames. This is a major concern
for any vessel that carries gasoline.
From a safety standpoint, we must consider that most small power boats
use gasoline, and most sailboats carry gasoline for their dinghies.
Your safety will be enhanced if you know how to handle this fuel and
adhere to very strict and thorough safety measures to prevent fire and
explosion aboard your boat. Taking out your Atomic 4 will not greatly
enhance your safety though, unless you also remove your dinghy fuel
and perhaps your stove fuel as well.
How do you use your boat? It is best to
buy a boat suited to doing what you do most often. It is probably a
mistake to buy a globe-circling bluewater cruiser if you sail weekends
with an annual two-week vacation. A coastal cruiser is better for this
kind of work. This reasoning applies to your choice of engines as well.
Don Moyer, of Moyer Marine, is a notable advocate of the Atomic 4. He
points out that a lot of older boats are being purchased by young buyers.
Many of these starter boats are “project boats” built in the
early days of fiberglass. Some are boatyard queens that are being brought
back from near-terminal neglect. They don’t cost a lot of money to buy,
but they will often require a great deal of owner labor to put them
back in shape. Many of them are smaller coastal cruisers, and many have
Atomic 4 engines. The engine is enjoying a resurgence of popularity. Click here to read more about Don Moyer.
It’s difficult and unreasonable to convince these buyers that they should
pay for an engine swap that may double the dollar investment in their
boat. The Atomic 4 burns about twice as much fuel as a diesel will burn
to go the same distance. On the other hand, how much fuel will a sailboat
use in a year? If you motor out of your marina and set sails, it is
hard to go through a tank of gas in a year of weekend and vacation sailing.
If you motor in calms and very light air, you will burn a little more.
Last year, we estimate that we motored Mystic, our C&C 30,
400 miles on summer weekends and a couple of two-week vacations. Without
being too precise with the math, it would cost $75 per year more to
feed an Atomic 4 than to feed our diesel. If an engine swap costs $3,000
to $6,000, the payback in fuel savings might take 40 years. And those
were used diesel prices. New diesel swaps go for roughly $6,000 to $9,000.
Like fuel efficiency, an argument about operating hours between major
overhauls favors the diesel. The cost of a major overhaul probably would
not favor the diesel but is more difficult to compare. More importantly,
both engines will run so many hours between overhauls that it is difficult
to be certain that either one will need an overhaul before a boat is
sold. The resale value of a boat may be greater if it has a diesel,
but there are still buyers for both. If the Atomic 4 is in good health,
the economics simply are not there for some owners of coastal cruisers
to convert to diesel before the engine needs to be replaced.
Mark Bressler is restoring Horizon, a beautiful
Tripp 30 designed by William Tripp Jr. When he bought the boat, the
engine had no compression to speak of. He determined that the exhaust
valves were stuck. Because the engine had been unused for a long time,
he feared other corrosion problems and replaced the original Atomic
4 engine with a used one that he located at a boat show.
He upgraded the replacement engine with electronic ignition and a higher
capacity alternator. He also installed a raw water filter “big
enough to grow fish in” and replaced the jacketed exhaust with
an injection elbow and a waterlift muffler. He also plans to add an
oil filter system and fresh water cooling. (The boat is presently operated
in Lake Superior where Mark does not think the raw water cooling will
cause much corrosion, but he has plans to someday use the boat in the
We asked him about routine maintenance. He said you need to change the
oil and make sure the engine gets good, clean fuel. This much will be
required by any diesel. Mark also said it is necessary to change the
plugs once in a while, but this task is not difficult, and the electronic
ignition makes the engine less fussy about plugs. What Mark didn’t say
was that among shade-tree mechanics and do-it-yourselfers, gasoline
engine repair skills are more common.
The routine maintenance on either type of engine is not particularly
difficult. Bacteria can grow in diesel fuel and will cause trouble if
it is not filtered out before reaching the injection system. On the
other hand, gasoline engines require occasional spark plug replacement.
In addition, the breaker points and condenser will have to be replaced
occasionally, if the engine does not have electronic ignition. And while
we are on that subject, it is worth mentioning that we have convinced
more than one reluctant Atomic 4 to start by simply wiping a clean cloth
between the points. It makes electronic ignition seem like a good upgrade.
The availability of parts is another matter. Both Alan Abrahamsson of
Old Lyme Marina and Don Moyer of Moyer Marine were cautious when asked
about availability of parts. Certainly, routine maintenance parts are
abundant. Major repair parts, such as blocks and camshafts, are available
now but may not be forever. Mark Bressler is keeping his old engine
The BoatU.S. catalog shows 20 common Atomic 4 repair items, including
gaskets, ignition, and pump parts. The Alberg 30 Web site: http://www.alberg30.org shows an extensive listing of spare parts
and where to obtain them. The parts in this list are cross-indexed to
Both Old Lyme Marina and Moyer Marine sell maintenance parts as well
as major replacement parts – such as blocks, cams, and cranks – but
these large components are salvaged from other engines. The future availability
of major parts is influenced by the fact that the tooling to efficiently
make these parts no longer exists. At present, good salvaged parts can
supply the demand. Don points out, however, that as younger buyers put
more older boats back in service, this picture could change.
There is no cause for panic at the moment. If the estimates are correct,
40,000 engines were built, and 20,000 are still in service. They can
draw on the other 20,000 for spares.
Tom Stevens of Indigo Electronics offers a broad selection of upgrade
parts for the Atomic 4. An electronic ignition, oil filter system, fresh
water cooling system, electronic fuel pump, and high output alternator
with a smart regulator are available. Indigo also offers a crankcase
vent system that works on the Atomic 4 and the Palmer P-60 4-cylinder
gasoline engine. The electronic ignition, in particular, enjoys an excellent
reputation. Tom started his accessory business by designing an electronic
ignition for the Atomic 4 – which did not always start as easily as
he would have liked – in his own Tartan.
Old Lyme Marina and Moyer Marine both sell rebuilt engines. These are
high-quality engines that have been completely torn down and gone through.
All components in these engines are inspected, evaluated, and replaced
as necessary. They can be expected to give many years of reliable service.
They list in the same price range as a used diesel. For many sailors,
they may be the best option, because they truly “drop in,”
while any diesel conversion will probably be more complicated and involve
Reliability and other aspects
The Atomic 4 has been criticized for not
having a center main bearing, and indeed no modern high-compression
engine is built today without a center main. In fact, some modern 4-cylinder
engines have five mains instead of two or three. The Atomic 4 is not
a high-compression engine however, and evidence suggests that it was
a well-designed engine. Very likely, the designers knew that the center
main would add several inches to the overall length of the engine and
chose not to make it longer if they could solve the problem another
Don has seen little evidence of broken cranks and recently sold off
a “basement full” because they were outlasting the blocks.
Alan says that cranks do break but the problem is really associated
with the condition of the exhaust systems of the boats. He says many
early exhausts were jacketed systems with a cooling jacket around the
exhaust pipe. If the exhaust pipe corroded enough to leak, water from
the jacket would enter the engine and get into the cylinders. If you
have this type of exhaust system on your boat, it would be advisable
to check it frequently for corrosion and, at the first suspicion of
trouble, replace it with a properly designed waterlift muffler.
Don points out that with any of the water-cooled exhaust systems, it
is important to close the cooling water seacock if the engine is going
to be cranked any period of time without starting. These situations
include the first start after launching in the spring, compression testing,
and any case of hard starting. The point is that the raw water pump
keeps pumping water into the exhaust system, and there is no combustion
exhaust to blow it back out again. In this situation, the exhaust system
can fill up and drain into the engine.
Naturally, as soon as the engine starts, the seacock must be opened
immediately to prevent the exhaust system for overheating.
At Old Lyme Marina, Alan says they sell all their remanufactured Atomic
4s with the Indigo electronic ignition upgrade, and he has never seen
one fail. As noted earlier, you can always wipe the points once in a
while, but if you like an engine that starts dependably, this upgrade
might be very attractive.
Alan also suggests that in boats where the fuel tank is higher than
the carburetor (the common arrangement), it is worthwhile to shut off
the fuel valve from the tank when the engine is not in use so if the
float gets stuck, the carburetor will not overflow.
Another potential problem mentioned on the Alberg 30 Web site was the
possible failure of the mechanical fuel pump diaphragm. If this part
fails, the engine will get fuel in the oil. An indication of this failure
is a strong gasoline smell on the dipstick. An electronic fuel pump
is available to eliminate this failure point.
The short of it is that the Atomic 4 is not a particularly unreliable
engine in its original form, and there are modern upgrades to make it
To put the issue of reliability in perspective, it should be understood
that few, if any, marine engines are as reliable and maintenance-free
as modern automobile engines. In the case of older marine engines this
statement is particularly true. Sailors should become familiar with
their engines and be prepared to spend time learning about and maintaining
Two other “aspects of use” are noise and availability of fuel.
Although newer diesel engines are quieter than they used to be, the
Atomic 4 is a very quiet and smooth engine. Depending on the replacement,
there may well be more noise and vibration with the diesel. We have
seen comments to this effect in some class newsletters. Also, because
the majority of pleasure boats are gasoline-powered motor boats, gasoline
is more readily available in some areas. Have you ever seen a public
fuel dock that had only diesel?
Good reasons to convert
The Atomic 4 is a good engine, but in some
cases owners may want to consider the diesel alternative.
If you convert to a diesel, the range of your boat for a given amount
of tankage will be roughly double. If you sail offshore or in remote cruising
areas where fuel is not readily available, this can be an important consideration.
If your boat is fairly large and/or valuable, you may find the diesel
option more appealing. Larger boats can effectively use the power of a
four-cylinder diesel and may have more room for one in the engine space.
Trading from the Atomic 4 to a four-cylinder diesel will not be as much
of a comedown in smoothness. If your boat is quite valuable, you may not
find the cost of conversion to diesel to be such an unreasonable percentage
of the total investment. In some cases the diesel may even be an expectation
on the part of your boat’s next buyer.
If you are going on an extended cruise where fuel costs may become a significant
part of your budget and where you may expect to do an unusually large
amount of motoring, a more efficient engine has a better chance of paying
for itself. The inland waterways of the East and Gulf coasts are examples
of places where a sailboat engine will see many hours of use.
There are several manufacturers making diesel engines intended to replace
the Atomic 4. Westerbeke, which bought the line from the original manufacturer,
sells both three- and four-cylinder engines for this purpose, and Kubota
offers at least one 25-horsepower model that has been known to fit. These
engines may or may not be drop-in replacements. Dimensional details should
be checked very carefully. Remember that it is not necessary to match
the 30-horsepower output of the Atomic 4. It was installed in a lot of
boats that could not use anything like the full power it can develop.
Determine your actual horsepower requirement by calculation.
Most diesels have a reduction gear, while many Atomic 4s did not. That
means that a larger propeller may be required, and it may need to spin
in the opposite direction. That is not all bad, but the tip clearance
between the prop and the hull needs to be kept in mind. It is beyond the
scope of this article to give all the considerations of converting to
diesel; suffice to say that it is not always simple and straightforward.
There are several good books on the subject, and there are yards that
do repowering which can be valuable sources of information.
The bottom line
Even though the Atomic 4 went out of production
about 20 years ago, it is still being extensively used in older sailboats.
It is well supported by rebuilders and parts suppliers, and it is well
known among repair people. In many cases it is logical to repair it or
replace it with another one rather than converting your boat to diesel.
The Atomic 4 is a well-designed good old engine for our good old boats.
Refueling safety is key to living with gasoline
by Jerry Powlas
Stringent safety measures should be taken by any boat carrying gasoline.
If your dinghy runs on gasoline, as most do, you have a boat carrying
gasoline. A few ounces of gasoline will make all the trouble you need. Whether the other 20 or 30 gallons on board are diesel or gasoline won’t make too much difference.
Kristen Chambers, Senior Project Administrator at the BoatU.S. Boating
Safety Foundation provided Good Old Boat with statistics on fire-related
boating accidents reported to the United States Coast Guard. She also
provided excerpts from Seaworthy, a loss prevention newsletter that
goes to sailors insured by BoatU.S.
The information provided by the Coast Guard does not distinguish between
gasoline and diesel accidents, but for 1995 and 1996, 79 incidents of
fire were reported. Of these, 61 involved ignition of spilled fuel or
vapor, 15 were categorized as failure to vent, and three were categorized
as fuel system failure. It is likely that the cases classed as “ignition
of spilled fuel or vapor” were cases involving gasoline, since
it is very difficult to ignite diesel fuel in this way.
Chapman’s Piloting, Seamanship, and Small Boat Handling offers a somewhat
elaborate procedure for refueling a boat. It may seem overly complicated,
but perhaps not when you consider that most accidents involving fire,
in the statistics noted previously, were caused while fueling or in
the first few minutes after fueling.
The basic idea behind refueling safety is to get all the liquid fuel
into the tank and to dissipate all the fuel vapors before making any
sparks or fire. Condensed somewhat, the Chapman version makes these
Before you fuel
- Before you fuel, inspect the fuel system, particularly the fuel fill and piping. A lot of trouble is caused by broken deck fittings or associated
piping and hose. Look also at the place where the fuel fill hose and
vent hose connect to the fuel tank. These locations are often below
the fuel level after refueling.
- Shut down anything that can make a spark or flame, and close up your
boat. Fuel vapors are heavy and will “spill into low spots.”
Remember that when you take on 20 gallons of fuel, you will displace
and emit roughly 20 gallons of fuel vapor.
When you fuel
- Make sure you put the fuel into the fuel fill. If you don’t do the
filling yourself, watch to see that this is done. People have been known to accidentally put fuel into fresh water and holding tanks. Other holes
that you would never consider – such as fishing rod holders and fresh
air vents – have also been the erroneous receptacles for gallons of
fuel. Don’t delegate this task.
- To avoid static charge buildup, make sure the nozzle is in metal-to-metal
contact with the fuel fill. Don’t use plastic funnels. Take portable
containers off the boat to fill them. Remember, too, that the fuel is
probably coming out of a ground tank and is colder than it will be later;
leave room for expansion in all tanks and containers.
After you fuel
- Stow portable tanks so they cannot be upset, no matter how violent
the motion of your boat gets.
- Ventilate your boat using your bilge blower. Ventilate until all
the fumes are out, generally at least four minutes. Since heavy vapors
will “pour into” low spaces, use your nose to sniff for fumes
in the lowest spaces on the boat.
- Do not start up and leave the fuel dock until you are sure you have
no problem vapors and all the fuel went into the tank(s).
If there is a spill
Open the battery switch. It’s a good idea to open it anyway during fueling
so fewer circuits are live and capable of causing sparks. Don’t turn
on the bilge blower in this case. It could make a spark or add enough
air to fuel vapors to make them explosive. Get the crew off the boat,
and don’t make any sparks or flames while cleaning up.
Finally, consider the spaces where you store all your fuels. Spaces
that store fuels should ideally be vented overboard at the bottom of
the space, in much the same way that propane is stored.
This next part is controversial. It represents Good Old Boat magazine’s
opinion. We had no problem finding disagreement with our opinion; we
offer it here anyway.
We suspect that the design of many boats did not anticipate the need
to store portable gasoline tanks. This may be particularly true of some
boats with diesel engines since we are told that diesel-powered boats
are not required to have ignition-proof components in the engine space. In our own observation, we see that the majority of boats have gasoline-powered dinghies, and we almost never see gasoline tanks lashed down on deck.
One industry authority told us (when reviewing this article) that the
improper stowage of portable gasoline tanks aboard sailboats is not
a problem, but we know that many good old boats really have no safe
place below decks to store portable tanks.