LETTERS TO THE EDITOR
helm to afford you real-time oil
temperature monitoring. Monitoring
systems like those offered by
Krill ( www.krillsystems.com) and
Maretron ( www.maretron.com)
include sensors that can keep
tabs on a variety of vital statistics
aboard your boat, including oil
temperature.—Steve D’Antonio
I really enjoyed Steve D’Antonio’s
article “The Quest to Burn Less Fuel.”
I have a few comments regarding
the matter of trailing an engine.
First, even if a transmission will
permit freewheeling, owners may
want to check the difference in drag
when the shaft is locked and when it
is freewheeling. A test I did years ago
on a 40-foot sailboat fitted with an
18-inch two-blade prop showed a
significant difference. Checking
speeds under sail, when the shaft was
locked we ran at about 4. 1 knots;
when freewheeling, the speed was 3. 7
knots. For this 10 percent gain alone,
it made sense to lock the shaft. For an
analogy, one can look at the aircraft
industry: autogyros have freewheeling
rotors that provide lift. This principle
also is at work when helicopters
make powerless emergency landings.
Second, on a twin-screw boat,
having less drag on one side will
mean less steering correction will be
needed. Another factor to consider:
transmission freewheeling should be
addressed if a boat is going to be
under tow for any length of time.
Lastly, years ago we fitted a 64-foot
ketch with a hydraulic shaft brake
that used gear oil pressure to “release”
the brake. (I cannot recall the brand
name of the brake, and I don’t know
if they are still made.) Our mistake
was getting the single-caliper model,
since the shaft would occasionally
break loose at higher speeds—when
surfing down a wave at 12 knots, for
instance. This unit was used in the
commercial fishing fleet and was
quite reliable.
John Simpson
www.simpsonmarinedesign.com
Delta, British Columbia
Thanks for your comments on
trailing an engine. I consulted with
a naval architect before writing the
article to discuss freewheeling versus
locked load/resistance. He basically
said it depends on several factors and
varies from boat to boat, and my hope
is that I expressed that in the article.
Many boat owners may find that they
have no choice but to lock the shaft
is the one source that puts it all together.
Glomex TV & VHF Antennas
Besenzoni Gangways
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