Comments below:

"Argonauta" wrote in message
...
Good to keep the paper charts. As you know, an onboard electronics
failure won't affect the paper charts one iota. I'm all for high tech
gadgets as long as the ones used for essential tasks have backups. As
for the others:

Knotlog - something else to clean under the waterline. The little
impellers seem to attract the most interesting growth. Useful for DR if
you don't want to be dependent on GPS.

There are two types of sensors for Knotlogs, one fairly new I think, that
uses electronics to determine haw fast water flows over the sensor surface
and has no paddlewheel or other moving parts. I saw something in SAIL about
them last year I believe.
The old tried and true paddlewheel sensor type can be set in a type of thru
hull that allows you to remove it while the boat is in the water to clean it
without sinking the boat.
Most removable sensors can be removed and a plug screwed in place without
letting too much water in, depending on ease access in the bilge and how
quick you are of course.