[Rhodes22-list] Looking for advice

[Roger Pihlaja]

Hi Alice,

I have the Autohelm ST-50 (Now Raytheon ST-60) tridata instrument.  The
tridata includes a knotmeter, mileage log, water temperature, & depth
sounder all in one display package.  I also have an Autohelm autopilot.  I
like the Autohelm series because of their proprietary "seatalk"
communications bus, which allows all the instruments in the system to share
information.  You may not care about having an integrated instrument package
now, but you might in the future.  This is good equipment.  Mine have been
bulletproof for over 12 years & counting.

In my opinion, a knotlog, depth sounder, & ship's compass are the minimum
complement of instruments your boat needs if you are going to take out of
sight of land.  The water temperature function  came with the tridata
package.  I wouldn't have bought it separately; but, it has turned out to be
surprisingly useful: for fishing, as a comfort gauge for swimming, & as an
indicator of when you have crossed into & out of currents.

What ever brand of depth sounder you get, make certain it has an adjustable
depth alarm.  That way you don't have to stare at it all the time.  It will
alarm when the water depth gets less than the setpoint.  This function is
also useful as an anchor alarm to detect if the boat is dragging its anchor
while you are sleeping.  Most digital depth sounders have at least one
adjustable depth alarm.

Another useful function on a depth sounder is an adjustable offset.  An
adjustable offset allows you to compensate for the difference in vertical
height between the depth sounder transducer and the deepest part of the
boat - usually the keel.  For example, I have my depth sounder setup to
indicate the water depth under the keel.  This function is very useful,
because in a stressful situation, you don't have to keep remembering to
subtract 20" from the water depth reading to know when your solid shoal
draft keel is going to touch.  Most digital depth sounders have an
adjustable offset function.

Some depth sounders are equipped with a "forward looking" function.  This
function is derived by keeping track of the last several depth readings and
extrapolating the trend forward in front of the boat.  In theory, this can
give you an early warning of a shallow area ahead.  In my opinion, this
function is of very limited utility in real world sailing situations.  I
certainly wouldn't pay extra in order to get it.

Finally, whatever brand of depth sounder you purchase, pay very close
attention to the installation instructions especially re the location of the
SONAR transducer.  The transducer can only transmit & receive its SONAR
signals in a relatively narrow cone.  If you mount the transducer on a
sloped part of the hull - like say the sharp V up near the bow; then, it may
lose the bottom return echo signal when the boat is heeled over on one
sailing tack or the other.  The transducer must also be in bubble-free
water.  I have my depth sounder transducer mounted approximately amidships
on the starboard side in front of the ice box.  It is mounted as far inboard
as the shoal draft keel permits.  I installed a 6" ID Beckson screw-in deck
plate in my cabin sole to permit inspection & maintenance of the backside of
the transducer.  The other preferred depth sounder transducer location is in
the lazarette compartment as far forward as possible & several inches to
starboard of the centerline.  You want to be as far forward as possible & on
the starboard side of the lazarette compartment to keep the transducer in
bubble-free water.  There are several sources of bubbles which may cause
problems for the transducer in this location: the cockpit drain, the
outboard motor exhaust when running in reverse, & waves slamming into the
transom when running before a following sea.  You also don't want to mount
the transducer so close to the centerline that it causes a structural
weakness between the cockpit drain thru hull & the thru hull penetration for
the transducer - keep them several inches apart.  If you mount the depth
sounder transducer in the lazarette compartment; then I would also fabricate
some sort of guard or cover to protect the backside of the transducer &
cable from being damaged by shifting cargo.  That's another favorable point
for the amidships mounting location - there's nothing rattling around under
the cabin sole that might damage the backside of the transducer or the
cable.

Good luck!

Roger Pihlaja
S/V Dynamic Equilibrium


----- Original Message -----
From: <AMICW at aol.com>
To: <rhodes22-list at rhodes22.org>
Sent: Tuesday, April 15, 2003 7:14 AM
Subject: [Rhodes22-list] Looking for advice


> Hi folks!  Hope to get delivery on my R22 soon and I'm considering a depth
> finder.  I know, from past emails, that many, including Stan, think this
is
> not needed however, I'll be sailing on the Chesapeake and would feel a bit
> safer with it.  For those who have (or want) one, what depth finder would
you
> recommend (don't need fishfinder - I do that on my own with a fishing
pole).
> Thanks.
> Alice
>
>