My 1980 SF takes on water and I cannot figure how. There are no cracks in the hull. I have a port which I need to drain water after every sail. How is the water getting in?
The soapy air bubbles will show quite clearly where the leaks are happening. In my case, I found a leak where the deck is attached to the hull and another where the splash guard is bolted to the deck.
Standing it on the stern should be no problem.. put something down to pad it so you don't point load a corner. Like... set it on a pair of the seat cushion tossable life preservers, a discarded couch/chair cushion or even a cheap foam pillow. Main thing is let the water out as fast as...
Usual culprits are the daggerboard trunk, bailer hole seam, gudgeon or a popped hull/deck seam. Check the chine carefully as well, sometimes there are crush spots there, the gelcoat looks okay but there can be microcracks in the fiberglass underneath.