A Few Answers
The O'Day 25 was built with the option of having an inboard, but I don't think a diesel was the original, gas SailDrives I think were the original equipment. I have a 9.9 outboard on my O'Day 25, and there are times when it just barely gets me by; however, with an inboard you have more weight, and the position would surely give less cavitation. I suspect you'd be fine with the 6.5 inboard diesel.The boat you're looking at is not actually a swing keel. It's a centerboard instead of a swing keel. A true swing keel has a heavy duty crank that pulls up a keel. The O'Day 25 has a 2 1/2 foot "trunk" keel that is lead and weighs 1825 lbs. The centerboard drops down another 3 1/2 feet, for a total keel depth of 6'. I believe the centerboard weighs only about 60 lbs.I know that sounds picky, but there really is a lot of difference both in design, and maintenance between a swing keel and the centerboard. Quite a bit of difference in performance too. The O'Day actually sails pretty well with the centboard up.Even if you don't trailer the boat, the centerboard model means you can sail it in about 3' of water (the rudder draws more than the keel does).