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.
