It looks like a standard packing gland
When tightened packing is compressed. If you've at the thread bottom you need new packing or in a half ass job, more packing. It's sold at any good marine
store that sell items for larger boats. Maybe a local marine
repair shop will know by experience the packing size without seeing the boat.
First determine if your bilge pump
will keep up with the flow if you remove the old packing. It wouldn't hurt to have a submersible pump standing by. One that has more than enough capacity to keep you afloat. And test it.
You'll get a little wet, but I would pull out the old packing before putting in new packing. You add enough packing to the point where the compression
collar will properly insert into the gland and just have enough threads to get the nuts fully on. Then tighten each side equally. Don't get ahead on one side. New packing probably doesn't need grease. I'm an old timer so bear with me. The rule
of thumb I was taught was tighten until when running there is a slight drip that translates into no drip when the shaft isn't turning. Don't just tighten until there is no drip and forget about it.
When running, check for too much heat at the shaft or packing gland
. Too tight packing can wear a groove in your shaft.