Oday 35 Main Halyard chaffing

[CodeGrue]

Over the last season, the part of the halyard that runs through the sheave at the top of the mast received quite a bit of chaffing. Inspection of the block revealed two potential causes:

- this line is the exact size of the sail track, so it may be getting caught and rubbing on the sides
- the exit from the sheave to the track is not tangentially lined up, so the line may be rubbing on the top of the mast

I find it odd that the sheave doesn't line up. It's recessed about a half inch from where I think it should be. I am not the original owner so I don't know if this is normal of if (possibly) the sheave was replaced with a smaller one from the original. Does anyone with a 34 or 35 have any insight?

I can't post a photo because it's in storage right now.

 

[dmax]

My previous boat was an '87 O'day 35, it had the Isomat NG1 masthead: NG1 Masthead Assembly
If you have the NG1, rige-rite can tell what sheave sizes to use.

It looked like this with the top cover removed - I replaced the sheaves but don't have the exact sizes but I believe they were 2" diameter, maybe an 1/8 more (they do use a 10mm shaft, not 3/8"). I'm pretty sure the middle sheaves were larger, closer to 3". I didn't have the alignment problems you are talking about. I used 5/8" halyards and had no chafing issues. If yours is the Isomat, make sure everything was put back together correctly - the shafts need to be pushed all the way down in their slots and the cap acts as a spacer to line everything up. Here's what mine looked like with the cap off, you can see the middle sheaves (fore-and-aft direction) are not lined up, the cap does that):

 

[CodeGrue]

Very helpful! Thank you do much for the photo. The schematics were not super clear.