I don't know anything about the DS1 stuff but I replaced my similarly
aged depth instrument (from space aged electronics!) last year and went
though the same thoughts and questions you are going though.

The problem is that transducer frequencies have changed over the years
and are now standardising at least for this year on just two frequencies
(50 and 200 KHz). It is very unlikely that your old system is either of
these or will match what a modern instrument needs. If the frequencies
of the old and new instruments are the same the transducer will probably
work. It is possible that there could be a power rating problem which
would cause you to destroy your old transducer but unless the ST40 has
some serious power output I would imagine it probably is lower power
than the old instrument and just more sensitive with better filters etc.

Most people didn't seem to think that trying the wrong transducer with
an instrument would cause damage but then again no one said it
definitely wouldn't damage it either!

In the end I just bought and fitted a new transducer which was hard work
because the new transducer was too short to go though my the fairing
block and hull so I had to make a new block and have a top hat nut made.
Any to cap it all the transducer lead was 4" too short! However, the
advantage of a new one it that you have a good chance that it will work.

Good luck.

bud wrote:
I am replacing the very old electronics on my 1977 Hunter 30 sailboat.

I want to use the Raymarine ST40 bidata instrument, but I wonder if I
can use the existing transducers for deptch and speed. The old depth
is a Standard DS1.

Any thoughts on this? If not reasonable, do I just install the new
through hull transducers and leave the old ones in? or remove the old
ones and try to fit the new ones in the same holes?

thanks,
Buddy E