LETTERS TO THE EDITOR
for example, when cruising in very
cold climates, the ∆T may be greater.
Generally, though, it’s a reasonable
rule of thumb that ∆T should be less
than 30, and it’s a standard builders
should strive to meet. Most engine
manufacturers specify a ∆T for their
installations. Many engine rooms
undergo what’s known as “heat
soaking,” meaning it may take as long
as eight hours for all the equipment
in the engine room to heat up and for
the temperature to stabilize. Exceeding
the ∆T means the engines lose some
efficiency, since warm air is less
dense than cool air and diminishes
the efficiency of the combustion
process. Also, a hot environment is
hard on all the other equipment in
the engine room; more heat means
a shorter life for components made
from rubber and plastic (hoses,
motor mounts, bushings, etc.), as
well as electrical gear.
The only way to know for certain
if your engines have enough air for
combustion is to place a manometer
in the compartment and to monitor
it to see if the pressure drops when
the engines (and genset) are running
at cruising speed. If the pressure
does drop, then the ventilation
arrangement needs to change, but it
may not be as simple as reversing the
flow of one blower. Ideally, the engine
compartment should remain at slightly
positive pressure. This ensures that the
engines have enough air to breath. If
the pressure is too positive, however,
you run the risk of forcing engine room
odors into the boat, and there will be a
greater load on the HVAC system.
If you don’t have a manometer, you
can perform a crude pressure test:
While at 80 percent rpm, open the
engine room door. If the rpm changes
even slightly (or if the door is difficult
to open, more difficult than when at
rest), it’s likely a vacuum exists, and
the engines may be operating in an
air-starved state. These days, with
nearly all engines being turbocharged,
a slight engine room vacuum isn’t
much of an issue, although it may still
affect a naturally aspirated generator.
Excessive heat, however, is something
to be concerned about. If it’s too
hot, a change should be made. This
may mean rearranging the forced
ventilation system or installing a
proprietary system that monitors
temperature and pressure and controls
fan speed and direction accordingly to
maintain optimum conditions.
FOR THE RECORD
We just sold our 44-foot Tollycraft
and are shopping for something larger.
It has become apparent that almost no
previously owned boats come with a
properly kept maintenance log. My
background is in small-airplane
aviation; of course, the FAA requires
logs for airplanes. The boats we are
looking at cost well over $1 million
new, but the records that are available
usually consist of a small pile of old
receipts and some anecdotes about an
engine overhaul or whatever.
A used boat would be worth a
lot more to me if there were decent
records. I bet you agree, but I have
not seen this mentioned in PMM.
Peter van Schoonhoven
Battle Ground, Washington
I could not agree more. The value of
having clear, detailed maintenance
records during your ownership of a boat
and when it comes time to sell cannot
be overstated. Such records can easily
be kept in a spreadsheet program such
as Excel, recording tasks and repairs at
specific dates and engine-hour readings.
Another option is to use a proprietary
program such as that provided by
SeaKits ( www.seakits.com; see PMM
