I think I would get bubbles, but I will check again. Mineral
oil is Airmar's recommendation, but they said they actually
like propylene glycol better! The trick these days is to find
some that isn't pre-mixed with water.
I can and will go slower. I did point out in another thread
that I have the base mounted about a foot off the midline. The
hull has a 20 degree deadrise. Maybe at high speed there is
more turbulence there than I thought. I can always move the\
base back closer to the centerline if necessary.
Thank you. Castor Oil will be my next try!
In general I am pleased with things. The in-hull TD sure beats
hauling the boat in order to insert the thru-hull, a $300 total for
me. I now do have a good bond with Silicon II.
Frank




On Thu, 3 Aug 2006 10:51:05 -0400, "GBM"
wrote:

Frank,

The answer may be to go a little slower when the depth is important

Regarding the medium, we always used Castor Oil. Use just 1/2 the bottle and
keep the other 1/2 in case this whole deal makes you sick. BTW, castor oil
has some special properties that make it useful for this type of
application:

http://en.wikipedia.org/wiki/Castor_oil

But, the mineral oil should be OK, unless it is quite thin. Try shaking some
up in a bottle and see if you get bubbles.

GBM


frank1492 wrote:
I tried using the silicone adhesive again and this time got a good
bond. (Bonding the base of an in-hull Airmar transducer to the
hull.) Filled with mineral oil (calling this the "medium") as per
instructions.
Here is what is happening. At low speeds, readings are good,
no misses, but at high speed, I get quite a few false readings, both
too high and too low. Is this a problem with in-hull vs thru-hull (I
seemed to get fewer false readings at high speed with the old
Datamarine transducer) OR is it related to bubbles in the medium or
improper contact between the transducer and the medium? I see
a lot written here about good choices for the medium (marmalade?)
Some ideas here would be most appreciated as usual.
Thanks to all for your past help. Looks like we're coming to the
end.
Frank