Any chance you can post a picture or two, give us an idea of the extent of this bubble?

Or a description of its dimensions?

Lacking that, 'Best Practice' would see you carefully cutting away the fiberglass and epoxy that's not bonded to your inner hull's surface, then sanding the hard edge left behind along with a small margin beyond that (maybe 1/2" - 3/4") as well as the epoxy that was underneath the bubble.

This all so that when you go to place a fiberglass 'patch' you've created conditions where the patch will be bonded well to the hull as well as providing an overlap onto what's already there surrounding the mis-applied area.

Carefully done there shouldn't be much to reveal the patch; as you say it's under the seat, even less likely to be noticed by anyone but yourself.

What's most important is that your inner hull's protected by a uniform layer of fiberglass and epoxy, both to prevent wear and tear as well as moisture intrusion into the plywood veneer under the fiberglass+epoxy 'armor-cladding'.

+1 on what spclark said. It's not a matter of looks, it's the survival of your boat. A bubble will eventually develop micro-cracks (if it hasn't already) Water will leak in and be trapped and the wood will rot. Bubbles also are the starting point for delamination and peeling.

In addition to fixing it the way spclark suggested (which, BTW, done with care can end up completely invisible even with a bright finish), sometimes it's also possible to use a hypodermic syringe with a fat needle and a very runny mix of epoxy and woodflour to fill the bubble.

When I've fixed bubbles that way I first put a small hole for the needle at one end of the bubble and a larger hole to act as a vent at the other end. I also tilted the boat to let the epoxy mix flow more easily. The most difficult part was getting hold of the hypodermic stuff, but anyone with a cat that needs subcutaneous rehydration therapy will have a supply of single-use IV needles that are perfect for this, so check with your friends who have older cats.

Good luck,

Laszlo

   Thank you for your help. I don't know how to post a photo to this forum but I think I understand now that I need to fix it, and cutting out and patching carefully will be the way to go...and my next challenge!

How to post pictures here explained in detail.

TLDR: Host your images as publicly shareable with your favorite web image hosting service. Get the picture's URL. In your CLC forum post click on the image icon (next to the question mark button when posting). Paste the URL into the pop-up and set Width to 500, hit OK.

Laszlo