Depending on the year MFR and on the fiberglass, some boats seem to be extremely affected by blisters.. On a early 80's H37C, there WERE no blisters - after spending a "life" in the water... On a '88 Macgregor 26 - there were some blisters.. but it had spent virtually NO TIME in Saltwater - and very little time in freshwater (trailer boat)...
My (limited - remember!!!) experience so far says to NOT SKIMP the process: that is - make sure the materials and procedures are something for the long term.... Otherwise, you might end up doing it again... The '88 boat is likely to be prone to possible blisters.. just was the type of material adhesive in the hull.. So it was important to:
- take it down (strip/sand) to the gelcoat,
- thoroughly clean/dewax, fix all the current problems (especially on any through
hull - or near through hull holes (or hardware mounts),
- apply barrier coat (interlux) (multiple layers)
- add touchup (ie, "more layers") on high wear sections - keel, bow, etc.
- bottom paint - with the right paint...
- do the stripes.. (tape)
This is an oversimplification.. and I did (do) this myself to really learn the process. it takes a lot more time.. and our time is worth something.. but I learned a lot.. I expect that I will be out $500 in stripper/epoxy/barrier coat/bottom coat/stripes/dewaxer-cleaner.. And you can add more for sanders/abrasives, tapes, tools, etc.. And you can add more for your time... I did this in the back yard - and have learned a LOT..
If you hire it done.. at least know what the materials, supplies, and equipment costs. That way, the quotes you get will not SHOCK you.... This is an expensive process. If you hire it done, you can write a check. Do it yourself - and you will learn how to bottom paint (and the next time - you will prefer to hire it out... )....
When done - I should be out less than $1K - and it will have taken about 2 months - over the winter - to do it... I only worked on it part time - and like any newbie.. it takes quite a bit longer - and I made mistakes..
Really.. it is CHEAPER to hire it out - if you are working for a living... just my $0.02 worth....
Next bottom job - I expect to just do the bottom coat - the other will have been done...
--jerry