It's been mentioned here before, I think; but I thought I'd toss this in anyway. After replacing a broken centerboard sheave on my 240, I noticed a great deal of difficulty raising and lowering the centerboard. Tracked the problem back to the sheave, which was too large for its allotted space. The sheave pressed tightly against the fitting through which the centerboard line runs and also pushed the line snugly against the mast plate (don't ask me why I didn't check these things prior to completing the installation in the first place). Anyway, the sheave simply would NOT turn and the centerboard line had immense difficulty passing back and forth across it. After fighting with this for two sailing trips, I finally removed the mast plate again, took out the offending sheave and filed it down at least a quarter inch all the way around (no, it doesn't look pretty and neat). Now the sheave turns freely and the centerboard line passes across it with no resistance. All- in- all, a twenty minute fix if the mast is down.