If you have internal halyards then you will need to leave clearance at the halyard exits (and near the top of the mast to make sure the halyards will not chafe on the end of the conduit (good idea to smooth/round the top of the conduit before you stick it in. Also the conduit has to fit past the compression tubes where the stays attach. I think I used 1-1/2 in the back to the top of the mast and 1-1/4 in the front to the spreaders when I did my mast on my 34' With larger size coax and conductors it does fill up pretty quick and the pop rivets I used leave a pin sticking into the conduit space so it is a good idea to go larger if you can within reason. I am pretty sure that more than 1-1/2 wouldn't have worked well with my internal halyards as some of them exit toward the back of the mast. It can be a real challenge to rivet it in place. I ended up having to drill two holes a few inches apart along the mast next to each other and used a self tapping screw to temporarily pull the conduit to the side of the mast before riveting the other. Then remove the screw and put in a second rivet.
Nathan S/V Wisper C&C 34
