: I am at the sanding stage, before glassing. I have scrapped and planed and
: have a relatively smooth hull. Since I am going to be glassing, how smooth
: should it be. If rub my hands against the strips, I can detect slight
: difference, but running with the strips they are relatively level. I
: assume this does not have to be furniture smooth as that will come after
: the glass.

It depends on how smooth a final result you demand. The smoother you make it at this point the smoother the finished result. By "smooth" I mean "fair". It can be smooth and only sanded to 60 grit. If you feel ridges when you run your hand over the surface, these will translate to ridges in the final finish. They are not a serious problem, but what you don't deal with now will be harder to deal with later if you decide you want to.

A subtle high/low spot will manifest itself in an uneven reflection in a highly varnished boat, and theoretically it could make the boat fractionally less efficient. If you are not to bound up with getting a "showroom" finish, don't worry about it. It takes a lot of work to get rid of the slight irregularities. It requires removing all the high spots to bring them down to the level of the lowest spot.

Careful scraping can do this but may lower the low spots just as quickly as the high spots for no net improvement. A soft backed sander also has a tendancy to remove material just as fast from low spots as high spots. A stiff backed sander will concentrate on high spots a little more. A large/long stiff backed fairly sander is quite effective at only taking off the high spots. A long, sharp "jointer" plane set shallow is also very effective for shaving off the top of high spots on relatively flat surfaces.

You can get really obsessive about it, but at some point you are just going to have to stop and go on to the next step. After you've got it "fair" it is time to sand to get rid of any sanding/scraping/planing marks or scratches. I've been sanding to 80 or 120. Finer will enhance the look of the wood by may cause bonding issues. Don't spend more than a day at the whole process. Even a day is probably too much time.