New to using SE-22. Need help with extracting surfaces from a mesh body. Object is a large racing boat which was damaged

[3DScanSTL]

I've scanned a large racing boat with which the hull is to be repaired. The problem I'm having is extracting some of the surfaces where damage occurred. I can get a couple of decent b-spline surfaces but I'm not having any luck using them to replace the damaged areas. I've tried all of the tools that seem like they should apply, such as trim, intersect and just trying to export the objects to use in another application to merge the surfaces. I wan to use the bspline surfaces to trim the scanned mesh so as to create a smooth, clean surface for the boat builders to create their repair panels.