Chances are, you like everything about it…with
one exception. Anyone who has ever owned a boat for more than a few
years will readily admit there comes a point when the possibility of
replacing an engine or two becomes a very real likelihood. To some,
the mere thought of replacing their tired gas guzzling engines with
a pair of new, fuel efficient diesels sounds great. To others, the
task may appear somewhat daunting. After all, re-powering any inboard
is a little more involved than simply dropping a new outboard on
your transom.
A Practical Approach
Engine selection is indeed important. However,
this guide was written to provide you with a solid understanding of
those things to be considered beyond engine size, horsepower, and
brand. It was written as a "how to" guide covering
everything from evaluating cost vs. the value derived, to selecting
an experienced and reputable installer. In spite of its perceived
complexity, re-powering doesn't have to be a hassle.
Engine Reliability is Paramount!
Marine engines must, above all else, be
reliable. Engine reliability is especially important in pleasure
boats, where the capability of the crew to deal with mechanical
problems may not equal that of crews on commercial vessels. Today's
marine engines have a long life; however, eventually either major
repairs or replacement may be necessary.
Cost Vs. Value
It may be tempting to think that the value of
a boat re-powered with a new engine will increase enough to fully
offset the cost of the new engine and its installation. Although the
boat will be worth more with a new engine, the increase in value in
the used boat market may not equal your investment if you sell the
boat. The same is generally true if you convert from gas to diesel.
The boat's value will increase, but probably not enough to fully pay
for the conversion. That said, you are considering the rebuild or
re-power because you want to use your boat, not sell it.
The Rebuild / Re-power Trade-Off
Although rebuilding an existing engine
normally poses a few challenges, the installation of a new engine
usually provides significant performance and economic ad-vantages.
Many parts and accessories of a rebuilt engine - alternator,
starter, water pump, for example - are usually retained, and have an
uncertain further life expectancy. All parts of a new power plant
will be unused and the entire engine will carry a very valuable
manufacturer's warranty. There are no hard and fast rules for
deciding between rebuilding an existing engine or re-powering with a
new engine. However, spending more than about 40% of the cost of a
new engine on a rebuild may not be a good investment.
Re-powering; Getting the Job Done Right
A successful re-powering project involves two
equally critical decisions:
Selection of a qualified installer and
choosing the right engine for the boat. Of the two, the
selection of the installer can be the more challenging. While
engines can be precisely defined by their specifications, the
installation of new engines requires reliance upon the
engineering judgment and the skill of those doing the work. The
project must be planned carefully in conformance with applicable
ABYC* standards. The work must be done right; "good enough:
won't do. The following suggestions may help you achieve your
goals in re-powering your boat.
Accept bids only from prospective
installers who have visited and carefully inspected your boat.
The prospective installer should have questioned you about the
way in which you operate your vessel. The overall reputation of
the yard, and in particular, their experience in installing the
type of engine you have chosen, are important factors in your
decision process. Ask for references, especially from owners of
boats similar to yours, and if possible, for installations using
the same engine family you are considering. Be sure that every
item described in the technical areas identified on the
following pages is enumerated on any proposal you consider. A
few items, such as the practicality of converting a gasoline
tank to diesel fuel, may have to remain undefined until the work
begins. To the degree possible, leave nothing to chance or to
"we will see about that later."
(*The American Boat and Yacht Council is dedicated
to enhancing boating
safety by providing standards, education and information to the
recreational
boating community.)
How Big An Engine?
While the search for an installer proceeds, you should
determine the horsepower
you will want in your new engine. Simply installing an engine
of the same power as the existing one may not be in your best
interest. Your power needs will, in part, depend on the type of
boat being re-powered. A displacement hull vessel is usually best
served with a new engine of about the same power as used
originally. unless the boat was seriously underpowered, installing a more
powerful engine will be unwise. In contrast, planing hull boats, which are very
sensitive to weight, may be able to take advantage of the significant power to weight
improvements made in diesel engines in the past few years. With today's
lighter engines, it is often possible to install a less powerful engine than the
existing power plant, while equaling and often exceeding existing performance. Alternatively,
installing an engine similar in weight and size to the existing engine can
provide substantially more power, boosting both acceleration and top speed. However,
keep in mind
that a more powerful engine may require stronger engine beds,
larger prop shafts
and propellers, additional fuel tank capacity and reworking of
the existing intake
air and exhaust system.
The Devil Is In The Details
A few basic considerations will help define your
re-powering
project.
*The engine must fit in the space available.
*The weight of the engine should not be much in excess of the
unit being
replaced, with less weight generally desirable.
*There must be sufficient clearance around the new engine for
inspection and
maintenance access.
Unless the new engine can be properly mounted on the existing
engine beds, new
beds will have to be designed and installed. The fore and aft
position of the new
engine must be carefully considered. In many instances, the
new engine may
actually be shorter than the unit being replaced. However
replacing a V-type
engine with a straight 6 can present fore and aft clearance
challenges. Insist that
the installation employ the engine mounts provided or
specified by the engine
manufacturer. These mounts have likely been designed to
minimize transfer of
noise and vibration to the hull of the vessel. Using
non-standard mounts in order
to "improve" the mounting position of the engine
may create more problems than
it yields advantages. In the event your present engine
installation transmits significant noise and vibration to the hull, you may wish to
consider installing a
drive shaft system that incorporates both thrust bearing and
CV joints as a part of
your re-power project.
Clean, Cool Air In, Hot Air and Exhaust Out!
It is tempting to believe that the engine compartment air
intake and heated air
removal and exhaust systems used for the existing engine will
suffice for the new power plant, even if it is no more powerful than its predecessor.
Unhappily, this is
often not the case. No engine benefits from operating with
restricted fresh air for
compartment cooling and combustion. Engine power unavoidably
decreases as
the temperature of its combustion air increases above 77* F. Many
original
engine compartment designs did not adequately address these areas
of concern.
The exhaust system can be one of the more critical areas in a new
engine installation. The diameter, and most important, the backpressure of the
existing exhaust
system, must be checked to assure that they meet or exceed the
requirements
specified for the new engine. These precautions are especially
important when a
turbocharged engine is being installed. Insist on a careful check
of the integrity
of any existing exhaust system components that will be reused. It
is far less costly
to make repairs during the installation of the new engine than
afterward.
Feed It Clean Fuel
Once assured that the new engine will be properly mounted,
supplied with a suffi-
cient flow of the coolest possible air and connected to a
suitable exhaust system,
consider the fuel supply, raw water cooling, electrical, and
instrument systems. If
the boat was previously equipped with diesel power, the
evaluation of the fuel
system can be limited to a general check on its condition;
replacing any obviously
worn or deteriorated components, and if necessary flushing and
cleaning the
tanks. Install a fuel water separator/pre-filter and priming pump,
if none existed
previously. Avoid the all too common mistake of installing and
excessively fine
filter element in the pre-filter. Your new engine will have an
integral final fuel
filter. Use a 30 micron filter element in the pre-filter. It, in
combination with the
typical 5 to 10 micron filter on the engine, will fully protect
the fuel injection
system while affording maximum filter life.
Gasoline To Diesel Conversion
Re-powering a gasoline engine boat with diesels involves some
necessary addi-
tional work. The fuel system must be converted for use with
diesel fuel. Not
all tanks are built of material compatible with diesel fuel. A
fuel return line must
be installed from each engine to each tank. New fuel lines, water
separator/filters
and priming pumps will be needed. The diesel engine will likely
produce more
torque than the gas engine being replaced. Prop shafts may have
to be increased
in size. The rotation speed differences between gas and diesel
engines may make
it necessary to fit new transmissions rather than trying to use
the old ones. Similarly, it may be necessary to install new propellers to ensure a
proper match between the diesel's power and the boat.
Cooling Water For The Engine, Not In The Engine
The engine's raw water intake must be equipped with a proper
sea cock followed
by a raw water strainer, preferably one that can be opened
easily, without tools,
and which will reseal without the need for a new gasket. Be
certain that the new
engine installation design takes account of the height of the
engine relative to the
waterline. Engine installations that place the exhaust elbow near
or below the
waterline, must include a vacuum breaker/anti-siphon valve in the
raw water
discharge line, at a point prior to injection of cooling water
into a water cooled
exhaust system. This valve must be located where it can be
readily checked and
cleaned.
Instruments And Controls
A new engine will be supplied with a complete instrument
panel or a set of individual instruments. It is generally easier and less costly to
install the new panel,
rather than attempt to make the engine sensors operate existing
gauges and indicators. Pay particular attention to the tachometer installation.
Some engines
derive engine speed information from the AC current generated in
the alternator,
while others, such as Yanmar, take the more precise approach of
monitoring the
passage of gear teeth on the flywheel. Regardless of how
measured, accurate rpm
information will be critical in the process of selecting a
propeller.
The battery charging system of a new engine will likely mate
quite well with the
existing electrical system. However, it is advisable to check the
rated output of
the alternator supplied with the engine to determine if it will
cope with the
vessel's requirements for DC power. Often, the installation
of a new engine is accompanied by the desire to install
additional engine powered equipment; an
additional alternator, a refrigeration compressor, a reverse
osmosis water maker pump, etc. Check the engine manufacturer's
literature for guidance in this area.
Improperly applied external loads can damage the front
bearing of an engine. A
special mounting frame may be required to properly power
external, front of
engine loads.
The existing engine controls can most often be reused with
the new engine. However, they must be carefully checked for wear
and condition. In some cases, the engine stop control will have
to be modified from manual to electric or vice
versa.
Prop Shaft and Propeller
Depending on the choice of replacement engine, it may be
necessary to install a
larger propeller shaft, shaft log and strut. Especially in planning hull boats, a new
propeller may be required of the power or the weight of the new
engine differs
significantly from the one being replaced. Engines in some single
engine boats
are purposely installed at a slight angle from the longitudinal
centerline in order
to offset the propeller factor - the asymmetric thrust produced
by a propeller
rotating on an inclined shaft. If this is the case, be sure the
new engine's rotation
direction is the same as the original installation. When
necessary, this can be
accomplished by choosing a gear box capable of operating with the
same gear
ratio and efficiency in either direction.
The BIG DAY - On Water Performance Checks
A new engine installation is not complete until its
performance has been checked
on the water, and the operator has become familiar with the
proper management
of the new power plant. The sea trial must include operation at
all power levels, a
careful check of cooling system operation, exhaust system
performance and back
pressure, adequacy of combustion air supply and maintenance
of acceptable engine compartment temperature, ability to draw
from all fuel tanks, ease of starting, shifting, rpm at wide
open throttle and shut down. The manufacturer's
initial operating procedures must be well understood. Be sure
to check with the engine manufacturer regarding operation during
the initial 100 hours. Many new engines are damaged by being
operated at insufficient power levels during their initial use
period, when moderately high power operation is critical to
proper seating of the piston rings.
Check List:
*Realistic power level:
Available power at maximum rpm, -200
and -400 rpm,
time limits (if any) at these power levels.
*Engine size, weight, shape:
Will it fit easily into the
available space?
*Shaft rotation:
Does it match the existing installation?
If not, is there a
dual direction gear box available?
*Exhaust system requirements:
Compare with existing
installation.
Consider displacement and maximum rpm limits for both existing
and new
engine.
*Engine compartment design:
Adequacy of fresh air supply,
exhaust of heated
air, noise trapping of air intakes and exhausts, improvements
likely to be required / desired.
*Position of engine components relative to existing engine and
constraints
of engine compartments:
Will extensive rerouting of hoses,
cables and controls
be required? Will it be possible to gain access to the engine's
components for inspection and service?
*Engine controls and indicators:
Can the controls and
indicators for the new
engine be readily integrated into the existing panels?
*Adequacy of existing fuel system:
If already diesel, is
system in good condition? If power of new engine is significantly greater than that
of the existing
engine, will the present system hold enough fuel? If gasoline,
will the existing
tank material be suitable for use with diesel fuel? Can the
required fuel return
lines be added?
--From "The Boater's Guide to Successful Re-powering",
published by
Yanmar® Diesel America Corp.