It sounds like it split a seam that's there from the manufacture of the
boat.
If it's not accessible from the inside the only way is grinding & glassing.

Remove any paint in the area & clean the area as best as you can. Locate the
crack
& with the edge of a medium grinding disk "V" out the crack making sure you
get all
the crack. In other words make sure you grind till you get to solid glass.
Lay glass into
the crack but you'll probably only be able to do it in stages, especially if
the boat is on
a trailer or stands because your working upside down. Once cured grind the
repair till flush
then remove around the entire area of the repair enough material to lay over
at least 4 layers
of glass over the entire surface. Grind when cured, use any of the many
waterproof fairing
compounds to finish the repair.

Then, & this is where many people mess up! Don't just paint over the repair!
You must put
either gelcoat, barrier coat, or something to stop water from seeping in
there or else in a few years,
maybe sooner all your work will be for naught. Most people don't do the
final & most important
step because they think bottom paint will stop the water. Then they find out
the truth later.

Hope this helps.

Bill
wrote in message
...
Hi folks:

I just purchased a used fiberglass boat and noticed a 12 inch long
crack that runs along the keel of this boat. While investigating the
area, it looks like the damage was caused by loading this boat onto
its trailer and hitting a roller a bit too hard. This has also
created a soft spot in the middle of this long crack.

I'm wondering if somebody can share with me a step by step procedure
of how I should repair this?

Also, when trying to see the damage from inside the boat, I noticed
there's an elevated layer of fiberglass (maybe 3 inches) above the
area of the damage. If I was to try to repair this from inside the
hull, it looks like I would need to somehow cut into this elevated
layer.

Thanks for your help!

Clark