Well I had a branch collide with my tandem this spring, creating a 10" wide Y-shaped crack. You'll receive many better posts from experienced builders, but here's what I did:

• drilled 2 ~1/4" holes astride the cracked area,
• made 2 pieces of  ~12" x 4" x 3/4" wood with matching holes  
• made similar pieces of sheet polyethylene  - you could just as well use poly sheet
• saturated the cracks with epoxy and clamped the area as a sandwich of wood-poly-hull-poly wood by passing long bolts through the holes and tightening with nuts
• When I removed the bolts & clamps and peeled off the poly the area was pretty flat. 
• I plugged the holes with dowel stubs, filled in the cracks with 'peanut butter', sanded the area down (both sides) to the wood,resanded flat, repeat...
• Covered inside with glass and outside with carbon fiber, sanded, etc
• Painted and varnished 

Cracks are still apparent through the bright finish, if you look. I like to think it looks 'experienced'.

It may be harder to fix the typewriter...

Worst case'd have you cutting out the damaged panel(s), fitting new material then finishing the repair to where your satisfied. Short of that what you describe might be sufficient, as long as it's sound.

Good thing the house-mover didn't drop a house on your boat! Typerwiter's (really? You still own one? Or an antique just for display?) bad enough if not a vintage portable like the Olivetti that got me through college some 50 years ago....

 As spclark says, it depends on the extent of the damage. In my boat the cracks were limited to a single panel, none of which had actually been detached. The inward pucker was less than 1/2" so the dent could be forced flat & cemented nearly flush.

I never go boating without my typewriter. 

���Typewriter? What's a typewriter?

I wonder if my college years might have gone better had I had an Olivetti instead of a Smith Corona?   

The old Olympia manual which got me through college would have gone straight through the hull and kept on going, no doubt.  The solid old West German relic from the Cold War might have made a decent mooring, though that would have been a sad end for such a fine piece of machinery.

.....Michael

There's a good sequence of photos and descriptions that follow the repair of a badly damaged Annapolis Wherry over on Facebook.