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Storm Search(22-3)
By Steve Horsfall
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The 2006 season was my
first year back on the water in almost 30 years. The
urge to cruise became too strong, so I bought a 1970
27' Chris Craft Com-mander and had the best summer.
In July, I experienced lightning storms on the water
and while it was quite the show, it was pretty scary.
What is the full danger of lightning out on the water?
I asked around and as most people at the marina have
had similar experiences, no one knew what a lightning
strike would do to a pleasure craft and the odds of
it happening. I'd sure like to know.
R. Craddock (e-mail)
This is not my area of expertise, but I have had some
experience with lightning on the water. As on land,
the highest point is most likely to receive a hit and
sailboat masts are common targets. I have seen one powerboat
hit by lightning (on the windshield frame) and it damaged
the onboard electronics, the upholstery and fiberglass.
During my 30-plus years at the marina, I was a volunteer
with the Coast Guard Search and Rescue and spent many
stormy nights on Big Rideau Lake without even a near
miss occurrence. If any readers have had any scientific
data on this subject, let me know and I¡¯ll pass it
along in a future column.
SPEED DETERMINATION
Is there a way to determine the approximate
top speed of a boat using the engine horsepower, hull
construction, length and weight of the boat?
e-mail
Engine manufacturers produce propeller recommendation
charts that give approximate speed based on the weight
and length of the boat for all of their engines. These
are used to help the dealer (or the do-it-yourselfer)
to select the correct propeller for a boat and engine
combination. However, they can also be used to give
you the information you desire. Check with your engine
dealer for the applicable propeller guide. The correct
propeller plays a very big part in getting the most
performance for any given boat/motor combination. If
your boat and engine package is a relatively common
one, the dealer may be able to order a factory test
report on your rig. Also, keep in mind the hull shape
and bottom drag are two important factors that make
accurate theoretical ratings very difficult to estimate.
ON THE SPIN
I am having a dilemma choosing the right prop.
I have a 1988 Johnson 40 hp VRO J40TELCCS powering a
15-foot aluminum bass boat. The old propeller was a
stamped Michigan 012040 11-1/2 x 19. I was looking for
information on the Internet and found three different
propellers for the same engine. They were an 11-3/4
x 17, 11-1/2 x19 and 11-1/4 x 21. Which propeller will
give me the best performance?
G. Malave (e-mail)
In order to select the right propeller to achieve top
performance, you need to determine the maximum rpm you
are currently getting at wide open throttle with the
prop you are using now. With your engine, it should
produce approximately 5,300 rpm, but check your manual
to be sure. Now, if your current rpm is close to this,
then your current 19-inch pitch propeller is fine. If
it¡¯s not in the range, then going down to a 17-inch
pitch prop will raise your rpm by about 400 rpm and
going to a 21-inch will be about 400 rpm lower than
your current set up. You should try to get as close
to the rated maximum rpm without going over. Running
at higher than normal maximum rpm will not give you
the best performance overall and can cause engine damage.
MILESTONE COLUMN
This marks the 100th Ask the Experts column
since I started writing for Power Boating Canada. It
seems like only yesterday when a discussion with PBC¡¯s
Richard Crowder led to a trial feature, which has since
become a regular column in every issue. To all those
who have written letters, faxes and e-mails over the
years, thank you! Each letter gives me the opportunity
to help, not only the boater who wrote it, but to the
many others who may have had a similar question and
found some useful information on other topics. I hope
you will continue to write as we start on the next 100
columns of Ask the Expert! Cheers!
Steve Horsfall
Got a question or a problem? Send your inquiries
to Steve Horsfall at stephen.horsfall@sympatico.ca Fax:
1-613-236-0700. (Page
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