Hi Ariel, 

can you let us know what the boat is that you are taling about.  is it a kayak?  and if so, what model?  we can help if we know a bit more.  also, posting a picture will help.

h

 It is a Jimmy skiff. Attempt at photo below which shows the location, but not the size (could fit a finger through. https://photos.app.goo.gl/cA86eETfZ9LqHVoz8

Hi Ariel, 

i looked at your picture.  it does not look bad and this is not uncommon for a seat fitting on this kind of a boat.

there are a couple ways to address this....and it sort of depends on how big your finger is and how big you expect your fillet to be.

one approach is to make a very dough/peanut butter/putty like intial fillet with epoxy that is firm enough that you can basically close that gap.  you would first paint the area where the unthickened epoxy to start (this ensures the putty consistency plug will bond to the wood).  then in the same operation, you would create the putty mixture and trowel it into the gap.  you goal is to simply bridge the gap and then let this initial fillet harden.   you then come back with normal filleting technique and consistency.....and finish filleting the seat in.

if you think the gap is too large for the approach just described, you can take some scrap wood and fill the gap with it.  take the seat as is, bond some scrap to the gap area and shape it for a tighter fit.   make sure to coat the extra wood with epoxy to ensure it is sealed/waterproof. then just go ahead and fillet over it and make the filler big enough to hide the scrap that you used to fill the gap.

that said, i think you are in a good place....and it will come out fine.

h

   see answer above

   Thank you! It sounds like the first technique is likely to do the trick based on the size. Much appreciated!!

   ".....about to install fordeck but it doesn't fit flush into the stern......"

Foredeck is in the bow and stern is in the back of the boat at the transom. You had me confused my Jimmy Smith II didn't fit that way.  Your picture looked like a bow fit of a deck piece.  I used a stem piece of wood on the connection of the two hull halves and decks for ease of the bow tow eye  instead of a fillet shown in the instructions. That took care of any holes.

I would likely use hspira's peanut butter fillet and some fiberglass tape over the fillet. 

   PS.....if you use the peanut butter put some thing underneath to prevent falling through.