re-reeving halyards, with mast up?

[Robert Wilson]

Sssssshhhhhh. Don't give them an opportunity to meddle!

 

[Norman_E]

Keep all existing lines, but particularly the the first mousing line, as taught as possible, which may make it impossible for the second mousing line to entwine with the first/any others.
Making sure I'd solved the twist(s) was the big problem. The only way I could be sure was to start afresh with the main halyard (having removed the bottom sheave block) using the dropped weight and leaving a thin mousing line in place top to bottom, then capturing the main halyard and pulling it through the top WITH another mousing line.

You may be lucky by not having cross-braces within the mast - I wasn't! But you may find the top sheave assembly has some form of divider which needs to be dealt with.
Annoyingly, my long-awaited "cheap" borescope arrived the day AFTER I'd done the work. Sometime, when the mast is down, I'm going to thoroughly inspect the inside of my mast with it.

Good luck

Thank you for that. You have just reminded me that the borescope I have on board will go through the halyard exits and should give me a chance to see which way the twist goes. There is a divider in the mast crane, so I cannot just switch the halyards over at the top.

 

[Robert Wilson]

Thank you for that. You have just reminded me that the borescope I have on board will go through the halyard exits and should give me a chance to see which way the twist goes. There is a divider in the mast crane, so I cannot just switch the halyards over at the top.

Sadly no, but at least you are aware of it! That is why I had to remove the top sheaves to make sure that re-reaving the stringy bits went the correct sides of this divider. It was huge leap of faith to let go of the existing halyard and topping-lift, but logic, pain and cool calculation aided the task of pulling through the soon-to-be redundant stringy things!
I'm afraid your only option is to climb the mast and dis-assemble the top sheaves so that you have a clear and unobstructed path to re-reaving.

Your borescope will be a huge advantage over my "fishing-in-the-unknown". Bear in mind that the "twist(s) be well above or below the reach of your borescope............
Once again, GOOD LUCK.

All I might add is that when all is successfully achieved one enjoys a huge feeling of relief and pride!!