Masthead sheave blocks

Hi, I am redoing the running (and standing) rigging on this boat. The masthead sheaves are original and setup for wire running rigging. I’ve read that the halyards need to be minimum 1/2” diameter. Unfortunately, this means there is not enough room in the sheave box for three new sheaves to fit. The original sheaves are 1/2” wide and new sheaves, for 1/2” line would need to be 5/8” wide, and there is not enough room for three of these in the sheave box. For all three sheaves to fit, the line has to be 3/8” diameter. Has anybody dealt with something similar? Could I do 3/8” for the halyards? Should do away with the sheaves and somehow install external blocks? Thanks in advance for your input.

Edited: I see I can do 7/16” so I’m going to do some math and see if I can fit the three sheaves since one sheave can be smaller for the reacher halyard.

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Hi Nicole - we use 3/8” / 10mm halyards on Calypso and Mischief. Nothing hitech - just polyester double braid. No issues.

Cheers,
Jeremy

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Unless I’m mistaken, the rule for 1/2" halyards is not so much about strength, but about being easy to grab with your hands.

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We replaced all of our halyards a few years ago and used the original (non-wire) sheaves and 7/16 inch polyester double braid and have no issues. I am sure I found 7/16 inch as a specification somewhere, but I’m not sure where. I just re-checked the BCC manual and couldn’t find it in there anywhere.
Cheers,
Mike