[3rdday]

It might be a combination of voids in the layup + osmotic blistering I see them on my 21 also if there is a higher concentration at & below the waterline those may be both, and if they exist above but more sparse those may be voids in the layup- Fiberglass was very new to the public/commercial when the 21s were built so I am sure there was a learning curve. In any case a good barrier coat is important.