Originally Posted by hellosailor
I'm not sure I'd call prussicking up a mast unsafe though. If it was a short clear run--and his is short--heck, in a slimmer younger life, I've used them to go straight up street lamps that weren't tapered a whole lot more than many masts are.
Ya... you can do it... but prussic knots are friction based, and typically compress the rope they are tied around a little, while at the same time biting into them. Some forms of these style of knots cause the rope to make a slight turn, adding to the friction, and creating directionality to them. A mast won't allow the compression or slight bending effect for the prussic to the best choice. I think it would still work, but it might be pretty sketchy... and I wouldn't use it unless I didn't have another choice.
There is enough involved that I don't want to give the advice over the internet... please find someone there with more experience to help you with it. It will be safer that way.
As a side... be careful with the ascenders... some use little spikes to get grip on the rope, which works really well, and is completely safe, unless you shock load them, or try to use them while descending. I have seen rope sheaths stripped off perfectly good ropes this way... rendering them useless.
Sorry I can't help more.