Way to go Rnyk,
You nailed it. After seeing your last post, I went out and checked the mast tube on my Outback. It turns out there are two points that could leak. After shining a bright LED flashlight into the mast hole, I was surprised to find that there is a large Phillips-type machine screw at the bottom securing the aluminum mast tube to the bottom of the hull.
I poured about 1/8 cup of water into the mast tube (keeping the water level well below the two rivets at the top of the tube), but no leaks thru the bottom screw after 30 minutes. I then added more water, so that the water level covered the rivets at the top. Bingo-within about 30 seconds, water began oozing out from around the rivets and running down the mast tube into the hull!
I then crawled into the forward hatch (WOW-that sure is a tight fit!) to get the pic below. The pic clearly shows the water oozing out from around the rivet holes and running down the outside of the mast tube into the hull.
Sooo-bottom line is, as you suggest, when not sailing plug your mast tube with a rubber stopper or cork of some sort. But make certain you can pull it out easily-it would be tough to remove if it got wedged down in the tube.
So that should solve at least one leak source. Looking down the road, perhaps Hobie can come up with a plastic sleeve or insert of some sort that will fit inside the mast hole to solve this problem. I'm going to try to coat the inside of the tube where the rivets are located with some silicone to see if that might help, But, of course each time you sail, the silicone would get worn away, requiring a new application-but no big ting-so long as I remember to do it…
