I'm replacing my battery boxes. One is original from Donzi. The 2nd battery someone added later on. 2 of the holes they drilled for the screws went through the hull. They covered it up with what seemed to be 4200 or 5200 from the bottom.

I've drilled it out to 3/16" and I'm making sure it's good and dry. I've filled the other screw holes (that dont go through the bottom) with dowels and resin. Is there anything different I need to do to fix these since they go through the bottom? How much smaller should the hole be than the dowel? The others I drilled to 3/16 for a 1/4" dowel. It was tight but there in there. Should I do these any differently since they're all the way through. Should they be that tight?

The other holes I set the dowels ever so slightly below the surface and plan on filling them in with a gel repair kit. Should I do the same thing on the bottom of the hull. It's hard to see so looks arnt the most important thing, not leaky and rotting the hull is. Thanks for you help.

Not sure about doweling the bottom of the boat, I would think this type of repair requires grinding out and glassing. Is the hull cored?? If so maybe do the dowel thing, but definitely grind out, and glass both inside and out.

I would do it just like u did the others.
But after that sand the outside down a bit bigger ( 2x2 ") and throw a matt over it then smoth out and gel.
Same in the inside.

west systems makes a epoxy that is great for repairs like this, roll the dowel in the epoxy and drive it in the hole till you are almost flush with the hull, leave a space about .25 of a inch. let dry then get some fine grit paper to take the blush off the epoxy, then fill with gel paste mixed with the color of the hull [white] the exopy will not let water intrude

And the gel will not stick to epoxy ,,,,bad idea.

What do you use for the dowels? What do you use for the patch under gel coat? Regular dowels?

Have very similar repair required on transom but have 19 holes!

reg. dowls,,,,and just glas them in !!!!!