Are you talking the rudder
shaft? Does it look anything like this?
This is a typical packing system around a shaft. Small drips might be cured by loosening the lower jam nut then tightening the upper nut. If that doesn't work then you loosen the upper nut all the way, add a ring of packing (available at your chandlery
, but you will have to pull the nut up to measure the distance between the shaft and box to get the right size) then tighten all up again. If you are just adding a ring it can be done (carefully) in the water
. If you want to dig out all of the old packing and replace all of it (should probably be done at some point if it is really leaking) you probably want to do it out of the water (I'm sure lots of people here, including myself, have done it in the water, but if you've never seen one before that might be stressful).
If it doesn't look anything like this then you might want to post a picture.