On my cat ketch, my main (forward) mast is done in this manner, except I fabricated the tube myself from multiple wraps of fiberglass cloth around the aluminum mast.  First the mast is wrapped in a few twists thin, slippery plastic, then wrapped up with about, oh, I think it was maybe 10 wraps of 8 oz. cloth.  When dry, I wrestled and twisted and cussed the new fiberglass tube off of the mast, discarded the plastic, and had a perfectly fit tube.  I epoxied the tube to the mast step and up through the deck.  There's a drain in the bottom out to the bilge.

Works great on a small boat.

Hi Arne, My Corribee 'Trivial Pursuit' has a hinged mast with a external tube that slides over the join. Kind of opposite to this idea (which I like) but easy to raise and lower. See my album. PS if I knew how I'd post a picture, there are enough on the album to show how it works.

I've seen two examples of steel standing pipes being used to hold masts unstayed and lightly stayed.

The idea seemed to be to use Schedule 40 pipe from just above deck, (on one, it was 6" proud and the other about 8" proud of the deck) down to the keel, semi-permanently sealed to the deck (integral flanges throughbolted and sealed) , stepped onto the keel and 'draining' into the bilge. The mast was placed inside this pipe. 

The first one (unstayed) had a wooden mast.. the mast had been sealed with epoxy and fiberglass to a few inches above the flange, and then sealed and painted with epoxy paint the rest of the way up. 

The other was a steel mast which stepped onto the halfway point down, with an internal flange (I was told it was 50% the radius of the pipe and filleted on the bottom) and a througbolt).

The wooden mast was a bit smaller than the standing pipe, and it was held in place by wedges and a steel band above the standing pipe, which had 4 welded fittings on it that were bolted to the top of the standing pipe, before being covered by waterproofed canvas, and the base had a great big steel pin through it. I was told that the hole through the base of the mast ) about 300mm from the bottom) was lined with schedule 10 pipe and well sealed with epoxy.. aka he had over drilled the bore hole, sealed it with several coats of thinned epoxy, filled it with epoxy/cabosil, then underdrilled it something like 3-4mm all around and then installed the liner pipe.

The guy with the wooden mast put in removable inspection ports every 300mm or so from the deck, port and starboard. He told me he had gotten nervous about the wooden mast so he retrofitted them in one summer. This way, he can physically check teh masts condition without having to unstep it.

What do you folks think about setups like this? I'm asking about the general idea, rather then commenting on the material choices, etc. Clearly, we all can see both of these fellows tried very hard to make sure they wouldn't have a corrosion or rot timebomb on their hands, and that would be fairly important. I imagine you could make these out of fiberglass, aluminum, wood/fg, etc. 

These examples were old school fishing trollers (well one troller.. one sardine carrier) that had been retrofitted for sail, and the owners were.. you can imagine.. wanting to never have to worry about their masts while at sea.