Hi Mohammed,
Yes, I had the same problem you have 2 times: replaced the sensor
on the hull with the boat in the water 3 years ago and the sensor
on the keel this year during haulout.
The heart of these sensors is a thin piezo ceramic plate with 2
electrodes which is glued on one side to the rubber cap and the
other side is epoxied together with the cable in the housing. See
the enclosed sketch.
A possible reason that re-glueing the cap ( or filling the hole
with silicone) does not work is that the actual sensor, a piezo
crystal with very high impedance, should not be in contact with
seawater which conducts electricity
This sensor fails too often and this might why:
The rubber cap is a little smaller than the hole so it can move a
little and seawater can get to the side of the sensor. Over time
this dislodges the glue between rubber cap and crystal
I followed the advice of another member of this forum: when
mounting a new sensor fill the space around the rubber cap with
neoprene to make sure the water stays out and the rubber cap
cannot move anymore.
Hope this is helpfull,
Stefan Jeukendrup
sv Malaka Queen
SM2k #348 @ Newry, Northern Ireland
Op 06-10-2021 om 08:32 schreef Mohammad
Shirloo:
toggle quoted messageShow quoted text
Hi Stephan;
We were on a tight schedule to get to our
winter berth. I did re-install the cap under water to protect
the sensor. We were getting erratic speed readings afterwards.
We will be hauling out next year and will address it then. Did
you have an issue with your speed sensor?
Thanks
Happy Sailing;
Mohammad and Aty
B&B Kokomo
Amel 54 #099
The function of the cap is to protect
the underlying high impedance crystal on which it is
glued. That keeps the water and dirt out.
If your Sonicspeed still works first
check AGC and resistance, see the manual in the "files"
section.
If still ok I would not try to put the
cap back. Instead you could try to fill the hole where the
cap was with underwater silicone. The "art" is to make
good continuous accoustic contact with the exposed
crystal.
SM2k #348 @ Northern Ireland
Op 26 sep. 2021 07:41 schreef
Mohammad Shirloo <mshirloo@...>:
Does anyone know the function of the rubber
cap? Is this for prevention of damage or growth
on the main sensor, or does it have some other
functional role?
Respectfully;
Mohammad and Aty
B&B Kokomo
Amel 54 #099
I had exactly the same issue. My sonic speed
stopped working. I dove and found that I had
one big barnacle on the rubber cap When I
pulled on the barnacle the cap came off.
Amel told me to reattach it with silicone
sealant on the edges.
I didn't haulout to do that and waited
for about 6 months for a scheduled haul
out. I replaced the cap, but Sonic Speed
never worked.
On Sat, Sep 25, 2021, 3:48 PM Mohammad
Shirloo <mshirloo@...>
wrote:
Our speed sensor was a bit erratic after a
3 week stay in Venice. I dove in it today to
clean the rubber caps with my diving gloves.
The rubber cap came off of the forward
sensor and I was able to catch it before it
went to the bottom.
I need to put the cap on while in water,
until we haul out next year. It appears to
be just a pressure fit as I could not see
any sealant. The sealant may have just worn
off in the past 12 years. Any advice on how
to fit it back in under water, would be
appreciated.
i have added pictures of the part to be
reinstalled.
thank you.
