The Cal came with the 4" round DMI
instruments on a 6" spacing, speed
and wind position and strength. On my Santana525, I had installed
system, wind, speed, close-hauled, speed change, and depth. This
allowed for sailing to wind maximizing hull speed and VMG,
Make Good. I would adjust for VMG and when hull speed would start to
off a little, hull speed would raise and VMG would start to fall......
help define the width of the slot. You can use the same tactic
wind. I've had great luck with the Raymarine instruments and
have had to send back a ST30 speed display. I discovered that it would
working when the temp was below 40 f. I also discovered that I also
quit working at the same temperature. It’s hard to sail when you can't
your hands. The Raymarine service center replaced the board at no
which surprised me; it had been out of warranty for about 6 months. Back to the Cal....
I had installed a Raymarine 630 Chart plotter for winter sailing, the
level drops 50-60 ft on the annual tide thanks to the TVA. We have
flats that appear and yes you can get stuck on them. There are two
sailors, those that have been stuck aground, and those that will be....
display option on the 630 was the window mode that can be setup to
seatalk data from the instruments. The DMI instruments are pre
could not interface. I wanted to install ST60 instruments that could
communicate. When I bought the boat I installed the ST60 masthead
connector block and cable for the wind instrument and ran the cable
back to the bulkhead. I had the only boat at the dock with two masthead
sensors, one turning clockwide and the other counter-clockwise. The
mast head instrument worked and I was waiting to haul the boat to
change out the Speed transducer that was not comparible with the ST60
speed display. I liked the DMI transducer with its wider
paddle wheel being more responsive at low speeds. Thus the
idea of trying to combine the two systems.
The Raymarine had a Hall Effect 3 wire system and
a 0 to 12 volt output, the DMI is a magnetic reluctance unit with 2
signal output. I designed an analog circuit and had a PCB
made to adapt
the two and tried several modifications without success. I could
apply a signal to the BNC input and the LED would blink and the
Raymarine display would start to display speed. I simplified the
circuit as much as possible but could not get the speed transducer to
interface with the front end of the circuit.
many attempts to
design a compatible front end, I took the DMI apart and traced the
discover the magical required interface. The transducer
required an excitation current that I had failed to supply. I
modified the board again and this time it worked.
Not a pretty site but functional. The PCB turned out to be a good
breadboard for the required modifications. I have the final PCB version designed if I ever need a replacement. One of the interesting finds was that the display needs a 10K resistor across a couple of the terminals to activate the display. The Raymarine speed transducer has a 10k thermister so it can sense and display water temp. One easy option would be to replace the 10k resister with a thermister. Instead of water temp, it would display cabin temp.
options were to make an adapter plate and mount the
ST60 3 1/2" required holes into the larger 4" DMI holes or to use
the surface mount bezels which
required just larger square holes 4.3" x 4.5" than the 4" round
ones. I did CAD models to see what it would look like. If I used
the 1/2" or 3/4" starboard the instruments would protrude further from
the bulkhead and there was the possibility that the BNC
connector and cable would not clear the mounting hole. I had
soldered the connector at a 30 degree angle to help the clearance. if
for weeks and made a template out of 1/2" starboard to see what the
surface mounts would be like. I did not like the original ST60's
top mounted in the round holes. It looked just like an attempt to make
I took the top surface mounting
gray bezels off and put on the larger square flush mouunt ones.
snap in and out, but have additional mounting screws for the surface
mounts. The instrument housings were thicker than
1/2" so if I wanted to use the surface mount with an adapter plate
would have to be around 3/4" thick. I decided to router the
larger square holes in
the bulkhead and direct mount the instruments without an adapter board.
starboard template with the square surface mounting holes became my
router template and I used a ball bearing
1/4" by 1" long following bit to router the bulkhead
3/4" deep. The Cal was designed with a balsa cored bulkhead
approxamately 3/4" thick with an interior trim wall made of 1/2" teak
plywood. overall about 1 1/2" thick. I left the interior plywood alone
with the existing 4" round holes required for the original DMI
installation. I can add an inteior trim piece later.
It was easy to align the template over the holes for best
fit and tape it in place. I did discover that it could make quite a
balsa and a fiberglass went everywhere. I did a dry fit prior to
exposed balsa in the new routered holes. The countersinking
displays with the surface mounts allowed the instruments to sit deeper
in the bulkhead and the BNC connector on the adapter board allowed the
cable to attach easily. I was able to mount it almost flush to the PCB
Should I ever want to
reinstall the DMI instruments, I would have to make an 1/2" adaper board
with 4" holes on 6" centers. The DMI instruments are long enough
to allow for this and still have enough length for the installation
ring on the inside to secure them. You can tell from the inside photo how little overlap the top mount would have been. I really hate to put holes in a boat, or make small ones larger, but this time the results were worth it.
The instruments can communicate with the 630 chartplotter so I can
monitor the instruments while at the nav table. I'l add photos of the interior trim when I get that far. 7-27-09 E.R.