Try mixing a small amount of the old epoxy then spread it out and see if it cures the same as when you built the boat.  I would be surprised if it does and in that case you can get a container of the hardener (I don't think the resin deteriorates, only the hardener).  I would then test a small batch of that to make sure I don't have to scrape uncured epoxy from my hull.

I've just been doing the scuffs on my SW sport hybrid, and on the duckling's stems. I just lightly sanded off the paint, and touched up with left over epoxy, and tiny patches of glass where needed.

I wouldn't bother redoing the entire hull unless it is really well shredded, as you be adding weight but not strength.

My old epoxy had crystallised in the cold of the cellar but once it warmed up it was just fine.

just a quick note that agree with the recommendations above. 

keep the epoxy recoating limited to areas that need to be repaired.  just adding epoxy over good epoxy or sanding good epoxy off to replace it with new epoxy....doesn't really accomplish anything.

with respect to old epoxy,  test a small batch of epoxy prior to committing to applying it to your boat.  fwiw, i have epoxy that is over 7 years old and it still works fine.  i have always kept in in a cool place and not exposed to sunlight.

if you are coming up on needing to re-condition the boat, focus your efforts on fixing the scrathes and then getting a nice fresh coat of varnish back on the boat.  remember that you should be looking to have at least three coats of a high quality UV varnish to protect your boat.....especially if it sees a lot of sun. if not varnished, re-finishing the paint is another way to complete renewing your craft.

i have a couple boats that just passed their 10 year anniversary....and they look new.   but about every three to four years they get a really good re-do...but again, the focus is on scratch repair, paint and varnish and i will also re-do deck lines and bungees.

best,

howard  

Thanks for the replys.....I will try mixing a small batch and see how it cures. My basement is heated, so it stays 65 degrees winter, to 72 degrees summer, so I think I may be OK.  I will do the spot touch ups, I was going to do the the whole hull, but your common sense will save me work. I may or may not re-apply the varnish, except for the time on the water and rooftop, the boat is always returned to the basement, never stored outside. Not  that I think it's too delicate to be outside, I just have the room and easy access.   Thanks again