I installed a wind instrument sensor at the top of the mast this spring; with the mast down. Catalina (or the dealer) had left me a nice messenger line :), which made pulling the cable through the wiring tube a snap. With the mast in the boat, the problem I'd see, is the location of the hole on the lower end of the mast. On my boat, the hole is on the forward/port side. It's a pretty tight fit between the mast and the bulkhead, and there's already a wiring harness, antenna and TV cables coming out of there. It was a pretty tight fit even being able to reach inside the bottom of the mast to push it through. Not saying you couldn't do it, but, having done it with the mast off the boat, those are the challenges I think you'd face.

Good luck with it..!

I added a disc antennae to top of mast, dropping cable inside and fishing out to bulked tv cabinet. Works great!

Wally
I have been considering doing the same thing for some time.
There are two options - mount the antenna on the masthead or mount it above the decklight fitting at the spreaders (or in my case abve the radar dome which is mounted there.)

In any case if you look at the C36 Mk11 Charleston Mast Handbook you will see that there are 2 conduits installed in the front section of the mast (Mine is a furling mast).

The masthead conduit is 1" in diameter and ends about a foot from the base of the mast where you could drill a hole to fish the cable out at the bottom. I dont see this as a problem.

At the top I was told by Charleston you can take the top plate off the masthead (held by 6 screws) which will expose the conduit. Have a look at the Handbook and you will see a picture of the fitting.

According to them, simply drill a hole and drop the cable into the conduit and let it fall to the bottom. The conduit is big enough to take a coaxial cable I was told.
This is the bit that I am unsure of as in my case I also want to do it with the mast on the boat and with me at the top of the mast. If there is no messenger wire installed and for some reason the cable wont fall down I am not sure what options exist.

(You could do the same at the spreader but it would be more difficult to drill a hole and find the second conduit which runs from below the spreader fittings and also ends about a foot from the base of the mast in the front section.)

It would be good if someone can confirm my "theory" (especially the bit about taking the top plate off on the Mk11) as I am reluctant to go to to top of the mast in the first place unless it has a 100% chance of success.

If you can't get your wire down the mast, you might try tying some weights such as several larger nuts to a piece of string and seeing if that drops down - obviously with a string long enough to keep one end at the top. In any case, whatever you do, be sure to attach a messenger line that you can leave in there. That way, if you are able to fish something out you will be spared the hassle the next time. (I have messenger lines going every which way under my cabin sole, etc. - for the future.)

Another possibility would be to tie two messenger line strings to an existing wire and pull that wire either up or down the mast. If you can pull it all the way, then you can pull it and the other wire back.

I used a fish tape to pull a new masthead wire through the conduit. When I did that I also left a double length of nylon string in there so hopefully will have everything in place if I have to pull something else in future.

You need to figure out what is already in the conduits. If you have analog RADAR, which requires a thick cable you might find the conduits are already pretty full. When my mast was down last year, I had one conduit replaced with a larger diameter conduit to be able to accept more cables and left a messenger inside for future use.
John Meyer
Hilbre-2135 San Pedro, CA