stringers and support

[strandedturtle]

I have a speedboat of 70's extraction with stringers that are dammaged only in one area main center one has 1 inch dammage in limited areas but the next stringer is damaged for a good three feet and has some areas wet and dammaged with in 1 inch of the outer hull and possibly all the way thru in short 6 inch(at the most) area. This boat has been left out and setting before I got it. My questions

Can I work on this with out removing it from the trailer

Can I cut out the area all the way down to 1 inch and place in core replacement and then fiberglass it

Write all this and have everyone understand that I'm new to all this
previous boat have been small metal type