There are quite a few differences, but basically the same hull design for the most part. I'll name just a few that I'm aware of:
- The V21 has a built-in sort of bracket on the transom which gives it the extra foot
- The upper hull and liner quite a bit different. The sliding hatch on the front opens further allowing better access to the anchor.
- A little less freeboard over some V20 models due to self-bailing vs. non. I don't know if there is a difference in freeboard on a V21 vs. a self-bailing V20.
- The cabin is bigger.
- The windshield is different.
- V21 has the built in livewell and bait well which serve as seat boxes to which the seats are mounted.
- There is a star board type insert that fills the notch in the transom.
- If I'm not mistaken the V21 has an 8 ft beam and some if not all V20's have 8ft 6 inch beam??
That's about all I can think of right now. I started out with a 1975 V20 and now I have a 1994 V21 so I know the difference between these two fairly well but not so much about the differences regarding other V20 year models.