: It's pretty obvious. It gradually fills with water when using a
: spray skirt on flat water or in a pool.

One more thought, what did you seal it with?

I have settled on polyester and paint. I have found that it takes 3 coats of paint. I did one with 2 coats and it looked great. Just like you describe, it slowly took on water with a skirt but yet there was on obvious leak or damage. The water on the saw horse trick showed me I had lots of seepage, not really leaks. But dozens of water drops started to form on the hull.

Took it in the shop, turned out the lights and put a light inside the boat. I would see dozens of pin holes when I got under the book. Third coat solved it and now three coats is standard on the hull.