extend a stuffing box hose?

[ghostlymoron]

I think the OP rules this out a few days ago.
I'd also go for a new shaft (about £150)

insert a spacer between coupling and the gearbox flange to move the shaft 1" (or whatever) further out. If you've enough space between prop and rudder. This leaves the sterngland untouched with all its dog locking devices intact, the correct length of hose and the packing running on a new bit of shaft.

Or as NormanS says, fit a new shaft...

 

[vyv_cox]

insert a spacer between coupling and the gearbox flange to move the shaft 1" (or whatever) further out. If you've enough space between prop and rudder. This leaves the sterngland untouched with all its dog locking devices intact, the correct length of hose and the packing running on a new bit of shaft.

Or as NormanS says, fit a new shaft...

This will give an excessive overhang between the propeller and cutless bearing. Rule of thumb is that the overhang should not exceed the shaft diameter. I am aware that many installations do not obey this but it is likely to produce more resonance in the drive train.

 

[easton]

Good point, although as you say, I'm fairly sure most people have more than that (such as for mounting a rope cutter).

 

[neil_s]

If your shaft is badly worn in the stuffing box, it might also be badly worn at the outboard bearing. A new shaft would, in my humble opinion, be the best 'engineering' solution - and not awfully expensive. However, the stuffing box on my boat has no interlocking dogs and any torque is resisted entirely by the rubber hose. It also has a plain outboard bearing, so that if the rubber tube split or broke, the water leakage into the boat would be slight. If you have a rubber outboard bearing, then failure would result in serious flooding!