Welcome to the Sailnet community! You'll find a great deal of info here, not to mention a variety of opinions and a variety of opinions.
I see in Sailboatdata that your boat was designed by the company's founder, Joeseph McGlassen. Your '68 Islander 30 is a raised deck version of the 29, and '68 is the first year they were made. There aren't very many of them because they also had a run of only two years. I don't know a lot about your model and couldn't tell you whether your interior had been modified. You might be able to tell from the drawings of your model
Two years later, Islander began a long run of highly successful 30 footers that all shared the same hull but different interior layouts. These, however, are not the same hull as your 30.
Brent, Krusty, and Luc,
I don't know very much about your models. I'm interested in your thoughts on how they sail. Talk to me about the sails you have and what kinds of speeds you see in various tacks at a given wind speed. When do you furl and reef?
Having asked that of you, I'll pass on my own observations. My Islander Bahama 30 (a Bob Finch design) is a very forgiving boat but is a little tender. I need to start furling my 127% jib starting at about 11 kts of wind and need to reef the main at about 15 kts. Otherwise, it starts developing some significant weather helm and heels excessively (and slows down). In a 10 kt breeze, I manage about 5 kts on a beat and 6.5+ on a reach. At 12kts and higher I'll get to 7 to 7.2 kts on a reach, depending on how flat the water is. I am delighted that my relatively heavy coastal cruiser manages those speeds.
That said, it took me a good year of sailing it to figure out the best way to shape the sails to achieve best speed, and it took a change of head sail to the current 127% genoa (from a 155% genoa) to get the speeds I quoted. The old genoa is great in 5 kts and below but has to be furled so much in decent wind that it spoils the sail shape, and that huge cylinder of material ruins air flow over the leading edge. My boat develops the majority of its power from the jib rather than the main. The standard jib is 256 sq ft vs the 194 sq ft main, so of course the difference is even more pronounced with a genoa. Clearly, having a great head sail is critical to good sailing on the 30-2 and Bahama 30 models.
Enjoy your Islander!