[willy]

Just an observation, the stringers, refering to those two main bow to stern structural members require the ability to flex and still provide unity to the whole ideally should be made of one solid piece or at least a well bonded intragual repair. They do not solely provide compression strength from weight above as say a short section of floor support might.
They are the actual backbone of the hull to which all other supports and bulkheads connect.
Therefore any repair you should do should be able to be bonded directly and permanantly to the good sections in front and behind.
How does Sea Cast bond with the wood, or for that matter how does it bond to the glass encasing it?
If it does not I would never use it for stringers. Maybe a section of floor support like we get on the side of tank or something.
JMO