Depends on the area you've got to do, but a triangular scraper with a very sharp edge, use a file or oilstone, works well even without a heat gun. Just pares away the varnish. Excellent on things like rubbing strakes etc.
Heatgun, very sharp scraper, the tungsten ones from sandvik are very good. But as mentioned, triangular ones very shrp, not the thin steel ones a proper job one. I wouldnt let nitromors near my varnish, or boat for that matter, even the varnish type remover. Just be careful you do not burn the wood with the heat gun.
I used a hotair gun on my Heron. The insides are the worst. I used it on half power and kept it moving. If you use a triangular scraper, just radius the points very slightly and avoid gouging, especially on areas with a bit of curvature. Enclosed spaces are the very worst as the heat blows back onto your fingers.
Hah! That doesn't fool me. I happen to know for a fact that lakesailor bought a brand new boat as in pic three, and let it go to rack and ruin as in pic 1. These days his half-finished project as in pic two is still parked in the garage...
Well I knew it happened one way or another. Perhaps I got the pics in the wrong order.
(57' is a bit too big, with my wealth of experience, 57" would now present a challenge. I bought it sight unseen on eBay and had the chance to walk away when I saw it, but like a fool........)