When I bought Destiny Calls (2nd owner/1980 CS27) she had, like many 1970-80's production boats, gate valve thru hulls.

I replaced them all the first year save the two largest cockpit scuppers. I was afraid that it would be nearly impossible to get them off since getting the samller ones was such a chore.

After sailing 1997-99 down south, I finally changed the "big ones" and guess what.

One fell off without a wrench! Whew!